DRM Memory Management¶

Modern Linux systems require large amount of graphics memory to store frame buffers, textures, vertices and other graphics-related data. Given the very dynamic nature of many of that data, managing graphics memory efficiently is thus crucial for the graphics stack and plays a central role in the DRM infrastructure.

The DRM core includes two memory managers, namely Translation Table Manager (TTM) and Graphics Execution Manager (GEM). TTM was the first DRM memory manager to be developed and tried to be a one-size-fits-them all solution. It provides a single userspace API to accommodate the need of all hardware, supporting both Unified Memory Architecture (UMA) devices and devices with dedicated video RAM (i.e. most discrete video cards). This resulted in a large, complex piece of code that turned out to be hard to use for driver development.

GEM started as an Intel-sponsored project in reaction to TTM's complexity. Its design philosophy is completely different: instead of providing a solution to every graphics memory-related problems, GEM identified common code between drivers and created a support library to share it. GEM has simpler initialization and execution requirements than TTM, but has no video RAM management capabilities and is thus limited to UMA devices.

The Translation Table Manager (TTM)¶

TTM is a memory manager for accelerator devices with dedicated memory.

The basic idea is that resources are grouped together in buffer objects of certain size and TTM handles lifetime, movement and CPU mappings of those objects.

TODO: Add more design background and information here.

enum ttm_caching¶: CPU caching and BUS snooping behavior.

Constants

ttm_uncached: Most defensive option for device mappings, don't even allow write combining.
ttm_write_combined: Don't cache read accesses, but allow at least writes to be combined.
ttm_cached: Fully cached like normal system memory, requires that devices snoop the CPU cache on accesses.

TTM device object reference¶

struct ttm_global¶: Buffer object driver global data.

Definition:

struct ttm_global {
    struct page *dummy_read_page;
    struct list_head device_list;
    atomic_t bo_count;
};

Members

dummy_read_page: Pointer to a dummy page used for mapping requests of unpopulated pages. Constant after init.
device_list: List of buffer object devices. Protected by ttm_global_mutex.
bo_count: Number of buffer objects allocated by devices.

struct ttm_device¶: Buffer object driver device-specific data.

Definition:

struct ttm_device {
    struct list_head device_list;
    const struct ttm_device_funcs *funcs;
    struct ttm_resource_manager sysman;
    struct ttm_resource_manager *man_drv[TTM_NUM_MEM_TYPES];
    struct drm_vma_offset_manager *vma_manager;
    struct ttm_pool pool;
    spinlock_t lru_lock;
    struct list_head pinned;
    struct address_space *dev_mapping;
    struct workqueue_struct *wq;
};

Members

device_list: Our entry in the global device list. Constant after bo device init
funcs: Function table for the device. Constant after bo device init
sysman: Resource manager for the system domain. Access via ttm_manager_type.
man_drv: An array of resource_managers, one per resource type.
vma_manager: Address space manager for finding BOs to mmap.
pool: page pool for the device.
lru_lock: Protection for the per manager LRU and ddestroy lists.
pinned: Buffer objects which are pinned and so not on any LRU list.
dev_mapping: A pointer to the struct address_space for invalidating CPU mappings on buffer move. Protected by load/unload sync.
wq: Work queue structure for the delayed delete workqueue.

int ttm_device_init(struct ttm_device *bdev, const struct ttm_device_funcs *funcs, struct device *dev, struct address_space *mapping, struct drm_vma_offset_manager *vma_manager, bool use_dma_alloc, bool use_dma32)¶

Parameters

struct ttm_device *bdev: A pointer to a struct ttm_device to initialize.
const struct ttm_device_funcs *funcs: Function table for the device.
struct device *dev: The core kernel device pointer for DMA mappings and allocations.
struct address_space *mapping: The address space to use for this bo.
struct drm_vma_offset_manager *vma_manager: A pointer to a vma manager.
bool use_dma_alloc: If coherent DMA allocation API should be used.
bool use_dma32: If we should use GFP_DMA32 for device memory allocations.

Description

Initializes a struct ttm_device:

Return

!0: Failure.

TTM resource placement reference¶

struct ttm_place¶

Definition:

struct ttm_place {
    unsigned fpfn;
    unsigned lpfn;
    uint32_t mem_type;
    uint32_t flags;
};

Members

fpfn: first valid page frame number to put the object
lpfn: last valid page frame number to put the object
mem_type: One of TTM_PL_* where the resource should be allocated from.
flags: memory domain and caching flags for the object

Description

Structure indicating a possible place to put an object.

struct ttm_placement¶

Definition:

struct ttm_placement {
    unsigned num_placement;
    const struct ttm_place  *placement;
    unsigned num_busy_placement;
    const struct ttm_place  *busy_placement;
};

Members

num_placement: number of preferred placements
placement: preferred placements
num_busy_placement: number of preferred placements when need to evict buffer
busy_placement: preferred placements when need to evict buffer

Description

Structure indicating the placement you request for an object.

TTM resource object reference¶

struct ttm_resource_manager¶

Definition:

struct ttm_resource_manager {
    bool use_type;
    bool use_tt;
    struct ttm_device *bdev;
    uint64_t size;
    const struct ttm_resource_manager_func *func;
    spinlock_t move_lock;
    struct dma_fence *move;
    struct list_head lru[TTM_MAX_BO_PRIORITY];
    uint64_t usage;
};

Members

use_type: The memory type is enabled.
use_tt: If a TT object should be used for the backing store.
bdev: ttm device this manager belongs to
size: Size of the managed region.
func: structure pointer implementing the range manager. See above
move_lock: lock for move fence
move: The fence of the last pipelined move operation.
lru: The lru list for this memory type.
usage: How much of the resources are used, protected by the bdev->lru_lock.

Description

This structure is used to identify and manage memory types for a device.

struct ttm_bus_placement¶

Definition:

struct ttm_bus_placement {
    void *addr;
    phys_addr_t offset;
    bool is_iomem;
    enum ttm_caching        caching;
};

Members

addr: mapped virtual address
offset: physical addr
is_iomem: is this io memory ?
caching: See enum ttm_caching

Description

Structure indicating the bus placement of an object.

struct ttm_resource¶

Definition:

struct ttm_resource {
    unsigned long start;
    size_t size;
    uint32_t mem_type;
    uint32_t placement;
    struct ttm_bus_placement bus;
    struct ttm_buffer_object *bo;
    struct list_head lru;
};

Members

start: Start of the allocation.
size: Actual size of resource in bytes.
mem_type: Resource type of the allocation.
placement: Placement flags.
bus: Placement on io bus accessible to the CPU
bo: weak reference to the BO, protected by ttm_device::lru_lock
lru: Least recently used list, see ttm_resource_manager.lru

Description

Structure indicating the placement and space resources used by a buffer object.

struct ttm_resource_cursor¶

Definition:

struct ttm_resource_cursor {
    unsigned int priority;
};

Members

priority: the current priority

Description

Cursor to iterate over the resources in a manager.

struct ttm_lru_bulk_move_pos¶

Definition:

struct ttm_lru_bulk_move_pos {
    struct ttm_resource *first;
    struct ttm_resource *last;
};

Members

first: first res in the bulk move range
last: last res in the bulk move range

Description

Range of resources for a lru bulk move.

struct ttm_lru_bulk_move¶

Definition:

struct ttm_lru_bulk_move {
    struct ttm_lru_bulk_move_pos pos[TTM_NUM_MEM_TYPES][TTM_MAX_BO_PRIORITY];
};

Members

pos: first/last lru entry for resources in the each domain/priority

Description

Container for the current bulk move state. Should be used with ttm_lru_bulk_move_init() and ttm_bo_set_bulk_move().

struct ttm_kmap_iter_iomap¶: Specialization for a struct io_mapping + struct sg_table backed struct ttm_resource.

Definition:

struct ttm_kmap_iter_iomap {
    struct ttm_kmap_iter base;
    struct io_mapping *iomap;
    struct sg_table *st;
    resource_size_t start;
    struct {
        struct scatterlist *sg;
        pgoff_t i;
        pgoff_t end;
        pgoff_t offs;
    } cache;
};

Members

base: Embedded struct ttm_kmap_iter providing the usage interface.
iomap: struct io_mapping representing the underlying linear io_memory.
st: sg_table into iomap, representing the memory of the struct ttm_resource.
start: Offset that needs to be subtracted from st to make sg_dma_address(st->sgl) - start == 0 for iomap start.
cache: Scatterlist traversal cache for fast lookups.
cache.sg: Pointer to the currently cached scatterlist segment.
cache.i: First index of sg. PAGE_SIZE granularity.
cache.end: Last index + 1 of sg. PAGE_SIZE granularity.
cache.offs: First offset into iomap of sg. PAGE_SIZE granularity.

struct ttm_kmap_iter_linear_io¶: Iterator specialization for linear io

Definition:

struct ttm_kmap_iter_linear_io {
    struct ttm_kmap_iter base;
    struct iosys_map dmap;
    bool needs_unmap;
};

Members

base: The base iterator
dmap: Points to the starting address of the region
needs_unmap: Whether we need to unmap on fini

void ttm_resource_manager_set_used(struct ttm_resource_manager *man, bool used)¶

Parameters

struct ttm_resource_manager *man: A memory manager object.
bool used: usage state to set.

Description

Set the manager in use flag. If disabled the manager is no longer used for object placement.

bool ttm_resource_manager_used(struct ttm_resource_manager *man)¶

Parameters

struct ttm_resource_manager *man: Manager to get used state for

Description

Get the in use flag for a manager.

Return

true is used, false if not.

void ttm_resource_manager_cleanup(struct ttm_resource_manager *man)¶

Parameters

struct ttm_resource_manager *man: A memory manager object.

Description

Cleanup the move fences from the memory manager object.

ttm_resource_manager_for_each_res¶

ttm_resource_manager_for_each_res (man, cursor, res)

iterate over all resources

Parameters

man: the resource manager
cursor: struct ttm_resource_cursor for the current position
res: the current resource

Description

Iterate over all the evictable resources in a resource manager.

void ttm_lru_bulk_move_init(struct ttm_lru_bulk_move *bulk)¶: initialize a bulk move structure

Parameters

struct ttm_lru_bulk_move *bulk: the structure to init

Description

For now just memset the structure to zero.

void ttm_lru_bulk_move_tail(struct ttm_lru_bulk_move *bulk)¶: bulk move range of resources to the LRU tail.

Parameters

struct ttm_lru_bulk_move *bulk: bulk move structure

Description

Bulk move BOs to the LRU tail, only valid to use when driver makes sure that resource order never changes. Should be called with ttm_device.lru_lock held.

void ttm_resource_init(struct ttm_buffer_object *bo, const struct ttm_place *place, struct ttm_resource *res)¶: resource object constructure

Parameters

struct ttm_buffer_object *bo: buffer object this resources is allocated for
const struct ttm_place *place: placement of the resource
struct ttm_resource *res: the resource object to inistilize

Description

Initialize a new resource object. Counterpart of ttm_resource_fini().

void ttm_resource_fini(struct ttm_resource_manager *man, struct ttm_resource *res)¶: resource destructor

Parameters

struct ttm_resource_manager *man: the resource manager this resource belongs to
struct ttm_resource *res: the resource to clean up

Description

Should be used by resource manager backends to clean up the TTM resource objects before freeing the underlying structure. Makes sure the resource is removed from the LRU before destruction. Counterpart of ttm_resource_init().

void ttm_resource_manager_init(struct ttm_resource_manager *man, struct ttm_device *bdev, uint64_t size)¶

Parameters

struct ttm_resource_manager *man: memory manager object to init
struct ttm_device *bdev: ttm device this manager belongs to
uint64_t size: size of managed resources in arbitrary units

Description

Initialise core parts of a manager object.

uint64_t ttm_resource_manager_usage(struct ttm_resource_manager *man)¶

Parameters

struct ttm_resource_manager *man: A memory manager object.

Description

Return how many resources are currently used.

void ttm_resource_manager_debug(struct ttm_resource_manager *man, struct drm_printer *p)¶

Parameters

struct ttm_resource_manager *man: manager type to dump.
struct drm_printer *p: printer to use for debug.

struct ttm_kmap_iter *ttm_kmap_iter_iomap_init(struct ttm_kmap_iter_iomap *iter_io, struct io_mapping *iomap, struct sg_table *st, resource_size_t start)¶: Initialize a struct ttm_kmap_iter_iomap

Parameters

struct ttm_kmap_iter_iomap *iter_io: The struct ttm_kmap_iter_iomap to initialize.
struct io_mapping *iomap: The struct io_mapping representing the underlying linear io_memory.
struct sg_table *st: sg_table into iomap, representing the memory of the struct ttm_resource.
resource_size_t start: Offset that needs to be subtracted from st to make sg_dma_address(st->sgl) - start == 0 for iomap start.

Return

Pointer to the embedded struct ttm_kmap_iter.

void ttm_resource_manager_create_debugfs(struct ttm_resource_manager *man, struct dentry *parent, const char *name)¶: Create debugfs entry for specified resource manager.

Parameters

struct ttm_resource_manager *man: The TTM resource manager for which the debugfs stats file be creates
struct dentry * parent: debugfs directory in which the file will reside
const char *name: The filename to create.

Description

This function setups up a debugfs file that can be used to look at debug statistics of the specified ttm_resource_manager.

TTM TT object reference¶

struct ttm_tt¶: This is a structure holding the pages, caching- and aperture binding status for a buffer object that isn't backed by fixed (VRAM / AGP) memory.

Definition:

struct ttm_tt {
    struct page **pages;
#define TTM_TT_FLAG_SWAPPED             BIT(0);
#define TTM_TT_FLAG_ZERO_ALLOC          BIT(1);
#define TTM_TT_FLAG_EXTERNAL            BIT(2);
#define TTM_TT_FLAG_EXTERNAL_MAPPABLE   BIT(3);
#define TTM_TT_FLAG_PRIV_POPULATED      BIT(4);
    uint32_t page_flags;
    uint32_t num_pages;
    struct sg_table *sg;
    dma_addr_t *dma_address;
    struct file *swap_storage;
    enum ttm_caching caching;
};

Members

pages

Array of pages backing the data.

page_flags

The page flags.

Supported values:

TTM_TT_FLAG_SWAPPED: Set by TTM when the pages have been unpopulated and swapped out by TTM. Calling ttm_tt_populate() will then swap the pages back in, and unset the flag. Drivers should in general never need to touch this.

TTM_TT_FLAG_ZERO_ALLOC: Set if the pages will be zeroed on allocation.

TTM_TT_FLAG_EXTERNAL: Set if the underlying pages were allocated externally, like with dma-buf or userptr. This effectively disables TTM swapping out such pages. Also important is to prevent TTM from ever directly mapping these pages.

Note that enum ttm_bo_type.ttm_bo_type_sg objects will always enable this flag.

TTM_TT_FLAG_EXTERNAL_MAPPABLE: Same behaviour as TTM_TT_FLAG_EXTERNAL, but with the reduced restriction that it is still valid to use TTM to map the pages directly. This is useful when implementing a ttm_tt backend which still allocates driver owned pages underneath(say with shmem).

Note that since this also implies TTM_TT_FLAG_EXTERNAL, the usage here should always be:

page_flags = TTM_TT_FLAG_EXTERNAL |
TTM_TT_FLAG_EXTERNAL_MAPPABLE;

TTM_TT_FLAG_PRIV_POPULATED: TTM internal only. DO NOT USE. This is set by TTM after ttm_tt_populate() has successfully returned, and is then unset when TTM calls ttm_tt_unpopulate().

num_pages

Number of pages in the page array.

sg

for SG objects via dma-buf.

dma_address

The DMA (bus) addresses of the pages.

swap_storage

Pointer to shmem struct file for swap storage.

caching

The current caching state of the pages, see enum ttm_caching.

struct ttm_kmap_iter_tt¶: Specialization of a mappig iterator for a tt.

Definition:

struct ttm_kmap_iter_tt {
    struct ttm_kmap_iter base;
    struct ttm_tt *tt;
    pgprot_t prot;
};

Members

base: Embedded struct ttm_kmap_iter providing the usage interface
tt: Cached struct ttm_tt.
prot: Cached page protection for mapping.

int ttm_tt_create(struct ttm_buffer_object *bo, bool zero_alloc)¶

Parameters

struct ttm_buffer_object *bo: pointer to a struct ttm_buffer_object
bool zero_alloc: true if allocated pages needs to be zeroed

Description

Make sure we have a TTM structure allocated for the given BO. No pages are actually allocated.

int ttm_tt_init(struct ttm_tt *ttm, struct ttm_buffer_object *bo, uint32_t page_flags, enum ttm_caching caching, unsigned long extra_pages)¶

Parameters

struct ttm_tt *ttm: The struct ttm_tt.
struct ttm_buffer_object *bo: The buffer object we create the ttm for.
uint32_t page_flags: Page flags as identified by TTM_TT_FLAG_XX flags.
enum ttm_caching caching: the desired caching state of the pages
unsigned long extra_pages: Extra pages needed for the driver.

Description

Create a struct ttm_tt to back data with system memory pages. No pages are actually allocated.

Return

NULL: Out of memory.

void ttm_tt_fini(struct ttm_tt *ttm)¶

Parameters

struct ttm_tt *ttm: the ttm_tt structure.

Description

Free memory of ttm_tt structure

void ttm_tt_destroy(struct ttm_device *bdev, struct ttm_tt *ttm)¶

Parameters

struct ttm_device *bdev: the ttm_device this object belongs to
struct ttm_tt *ttm: The struct ttm_tt.

Description

Unbind, unpopulate and destroy common struct ttm_tt.

int ttm_tt_swapin(struct ttm_tt *ttm)¶

Parameters

struct ttm_tt *ttm: The struct ttm_tt.

Description

Swap in a previously swap out ttm_tt.

int ttm_tt_populate(struct ttm_device *bdev, struct ttm_tt *ttm, struct ttm_operation_ctx *ctx)¶: allocate pages for a ttm

Parameters

struct ttm_device *bdev: the ttm_device this object belongs to
struct ttm_tt *ttm: Pointer to the ttm_tt structure
struct ttm_operation_ctx *ctx: operation context for populating the tt object.

Description

Calls the driver method to allocate pages for a ttm

void ttm_tt_unpopulate(struct ttm_device *bdev, struct ttm_tt *ttm)¶: free pages from a ttm

Parameters

struct ttm_device *bdev: the ttm_device this object belongs to
struct ttm_tt *ttm: Pointer to the ttm_tt structure

Description

Calls the driver method to free all pages from a ttm

void ttm_tt_mark_for_clear(struct ttm_tt *ttm)¶: Mark pages for clearing on populate.

Parameters

struct ttm_tt *ttm: Pointer to the ttm_tt structure

Description

Marks pages for clearing so that the next time the page vector is populated, the pages will be cleared.

struct ttm_tt *ttm_agp_tt_create(struct ttm_buffer_object *bo, struct agp_bridge_data *bridge, uint32_t page_flags)¶

Parameters

struct ttm_buffer_object *bo: Buffer object we allocate the ttm for.
struct agp_bridge_data *bridge: The agp bridge this device is sitting on.
uint32_t page_flags: Page flags as identified by TTM_TT_FLAG_XX flags.

Description

Create a TTM backend that uses the indicated AGP bridge as an aperture for TT memory. This function uses the linux agpgart interface to bind and unbind memory backing a ttm_tt.

struct ttm_kmap_iter *ttm_kmap_iter_tt_init(struct ttm_kmap_iter_tt *iter_tt, struct ttm_tt *tt)¶: Initialize a struct ttm_kmap_iter_tt

Parameters

struct ttm_kmap_iter_tt *iter_tt: The struct ttm_kmap_iter_tt to initialize.
struct ttm_tt *tt: Struct ttm_tt holding page pointers of the struct ttm_resource.

Return

Pointer to the embedded struct ttm_kmap_iter.

TTM page pool reference¶

struct ttm_pool_type¶: Pool for a certain memory type

Definition:

struct ttm_pool_type {
    struct ttm_pool *pool;
    unsigned int order;
    enum ttm_caching caching;
    struct list_head shrinker_list;
    spinlock_t lock;
    struct list_head pages;
};

Members

pool: the pool we belong to, might be NULL for the global ones
order: the allocation order our pages have
caching: the caching type our pages have
shrinker_list: our place on the global shrinker list
lock: protection of the page list
pages: the list of pages in the pool

struct ttm_pool¶: Pool for all caching and orders

Definition:

struct ttm_pool {
    struct device *dev;
    int nid;
    bool use_dma_alloc;
    bool use_dma32;
    struct {
        struct ttm_pool_type orders[MAX_ORDER + 1];
    } caching[TTM_NUM_CACHING_TYPES];
};

Members

dev: the device we allocate pages for
nid: which numa node to use
use_dma_alloc: if coherent DMA allocations should be used
use_dma32: if GFP_DMA32 should be used
caching: pools for each caching/order

int ttm_pool_alloc(struct ttm_pool *pool, struct ttm_tt *tt, struct ttm_operation_ctx *ctx)¶: Fill a ttm_tt object

Parameters

struct ttm_pool *pool: ttm_pool to use
struct ttm_tt *tt: ttm_tt object to fill
struct ttm_operation_ctx *ctx: operation context

Description

Fill the ttm_tt object with pages and also make sure to DMA map them when necessary.

Return

0 on successe, negative error code otherwise.

void ttm_pool_free(struct ttm_pool *pool, struct ttm_tt *tt)¶: Free the backing pages from a ttm_tt object

Parameters

struct ttm_pool *pool: Pool to give pages back to.
struct ttm_tt *tt: ttm_tt object to unpopulate

Description

Give the packing pages back to a pool or free them

void ttm_pool_init(struct ttm_pool *pool, struct device *dev, int nid, bool use_dma_alloc, bool use_dma32)¶: Initialize a pool

Parameters

struct ttm_pool *pool: the pool to initialize
struct device *dev: device for DMA allocations and mappings
int nid: NUMA node to use for allocations
bool use_dma_alloc: true if coherent DMA alloc should be used
bool use_dma32: true if GFP_DMA32 should be used

Description

Initialize the pool and its pool types.

void ttm_pool_fini(struct ttm_pool *pool)¶: Cleanup a pool

Parameters

struct ttm_pool *pool: the pool to clean up

Description

Free all pages in the pool and unregister the types from the global shrinker.

int ttm_pool_debugfs(struct ttm_pool *pool, struct seq_file *m)¶: Debugfs dump function for a pool

Parameters

struct ttm_pool *pool: the pool to dump the information for
struct seq_file *m: seq_file to dump to

Description

Make a debugfs dump with the per pool and global information.

The Graphics Execution Manager (GEM)¶

The GEM design approach has resulted in a memory manager that doesn't provide full coverage of all (or even all common) use cases in its userspace or kernel API. GEM exposes a set of standard memory-related operations to userspace and a set of helper functions to drivers, and let drivers implement hardware-specific operations with their own private API.

The GEM userspace API is described in the GEM - the Graphics Execution Manager article on LWN. While slightly outdated, the document provides a good overview of the GEM API principles. Buffer allocation and read and write operations, described as part of the common GEM API, are currently implemented using driver-specific ioctls.

GEM is data-agnostic. It manages abstract buffer objects without knowing what individual buffers contain. APIs that require knowledge of buffer contents or purpose, such as buffer allocation or synchronization primitives, are thus outside of the scope of GEM and must be implemented using driver-specific ioctls.

On a fundamental level, GEM involves several operations:

Memory allocation and freeing
Command execution
Aperture management at command execution time

Buffer object allocation is relatively straightforward and largely provided by Linux's shmem layer, which provides memory to back each object.

Device-specific operations, such as command execution, pinning, buffer read & write, mapping, and domain ownership transfers are left to driver-specific ioctls.

GEM Initialization¶

Drivers that use GEM must set the DRIVER_GEM bit in the struct struct drm_driver driver_features field. The DRM core will then automatically initialize the GEM core before calling the load operation. Behind the scene, this will create a DRM Memory Manager object which provides an address space pool for object allocation.

In a KMS configuration, drivers need to allocate and initialize a command ring buffer following core GEM initialization if required by the hardware. UMA devices usually have what is called a "stolen" memory region, which provides space for the initial framebuffer and large, contiguous memory regions required by the device. This space is typically not managed by GEM, and must be initialized separately into its own DRM MM object.

GEM Objects Creation¶

GEM splits creation of GEM objects and allocation of the memory that backs them in two distinct operations.

GEM objects are represented by an instance of struct struct drm_gem_object. Drivers usually need to extend GEM objects with private information and thus create a driver-specific GEM object structure type that embeds an instance of struct struct drm_gem_object.

To create a GEM object, a driver allocates memory for an instance of its specific GEM object type and initializes the embedded struct struct drm_gem_object with a call to drm_gem_object_init(). The function takes a pointer to the DRM device, a pointer to the GEM object and the buffer object size in bytes.

GEM uses shmem to allocate anonymous pageable memory. drm_gem_object_init() will create an shmfs file of the requested size and store it into the struct struct drm_gem_object filp field. The memory is used as either main storage for the object when the graphics hardware uses system memory directly or as a backing store otherwise.

Drivers are responsible for the actual physical pages allocation by calling shmem_read_mapping_page_gfp() for each page. Note that they can decide to allocate pages when initializing the GEM object, or to delay allocation until the memory is needed (for instance when a page fault occurs as a result of a userspace memory access or when the driver needs to start a DMA transfer involving the memory).

Anonymous pageable memory allocation is not always desired, for instance when the hardware requires physically contiguous system memory as is often the case in embedded devices. Drivers can create GEM objects with no shmfs backing (called private GEM objects) by initializing them with a call to drm_gem_private_object_init() instead of drm_gem_object_init(). Storage for private GEM objects must be managed by drivers.

GEM Objects Lifetime¶

All GEM objects are reference-counted by the GEM core. References can be acquired and release by calling drm_gem_object_get() and drm_gem_object_put() respectively.

When the last reference to a GEM object is released the GEM core calls the struct drm_gem_object_funcs free operation. That operation is mandatory for GEM-enabled drivers and must free the GEM object and all associated resources.

void (*free) (struct drm_gem_object *obj); Drivers are responsible for freeing all GEM object resources. This includes the resources created by the GEM core, which need to be released with drm_gem_object_release().

GEM Objects Naming¶

Communication between userspace and the kernel refers to GEM objects using local handles, global names or, more recently, file descriptors. All of those are 32-bit integer values; the usual Linux kernel limits apply to the file descriptors.

GEM handles are local to a DRM file. Applications get a handle to a GEM object through a driver-specific ioctl, and can use that handle to refer to the GEM object in other standard or driver-specific ioctls. Closing a DRM file handle frees all its GEM handles and dereferences the associated GEM objects.

To create a handle for a GEM object drivers call drm_gem_handle_create(). The function takes a pointer to the DRM file and the GEM object and returns a locally unique handle. When the handle is no longer needed drivers delete it with a call to drm_gem_handle_delete(). Finally the GEM object associated with a handle can be retrieved by a call to drm_gem_object_lookup().

Handles don't take ownership of GEM objects, they only take a reference to the object that will be dropped when the handle is destroyed. To avoid leaking GEM objects, drivers must make sure they drop the reference(s) they own (such as the initial reference taken at object creation time) as appropriate, without any special consideration for the handle. For example, in the particular case of combined GEM object and handle creation in the implementation of the dumb_create operation, drivers must drop the initial reference to the GEM object before returning the handle.

GEM names are similar in purpose to handles but are not local to DRM files. They can be passed between processes to reference a GEM object globally. Names can't be used directly to refer to objects in the DRM API, applications must convert handles to names and names to handles using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GEM_OPEN ioctls respectively. The conversion is handled by the DRM core without any driver-specific support.

GEM also supports buffer sharing with dma-buf file descriptors through PRIME. GEM-based drivers must use the provided helpers functions to implement the exporting and importing correctly. See ?. Since sharing file descriptors is inherently more secure than the easily guessable and global GEM names it is the preferred buffer sharing mechanism. Sharing buffers through GEM names is only supported for legacy userspace. Furthermore PRIME also allows cross-device buffer sharing since it is based on dma-bufs.

GEM Objects Mapping¶

Because mapping operations are fairly heavyweight GEM favours read/write-like access to buffers, implemented through driver-specific ioctls, over mapping buffers to userspace. However, when random access to the buffer is needed (to perform software rendering for instance), direct access to the object can be more efficient.

The mmap system call can't be used directly to map GEM objects, as they don't have their own file handle. Two alternative methods currently co-exist to map GEM objects to userspace. The first method uses a driver-specific ioctl to perform the mapping operation, calling do_mmap() under the hood. This is often considered dubious, seems to be discouraged for new GEM-enabled drivers, and will thus not be described here.

The second method uses the mmap system call on the DRM file handle. void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset); DRM identifies the GEM object to be mapped by a fake offset passed through the mmap offset argument. Prior to being mapped, a GEM object must thus be associated with a fake offset. To do so, drivers must call drm_gem_create_mmap_offset() on the object.

Once allocated, the fake offset value must be passed to the application in a driver-specific way and can then be used as the mmap offset argument.

The GEM core provides a helper method drm_gem_mmap() to handle object mapping. The method can be set directly as the mmap file operation handler. It will look up the GEM object based on the offset value and set the VMA operations to the struct drm_driver gem_vm_ops field. Note that drm_gem_mmap() doesn't map memory to userspace, but relies on the driver-provided fault handler to map pages individually.

To use drm_gem_mmap(), drivers must fill the struct struct drm_driver gem_vm_ops field with a pointer to VM operations.

The VM operations is a struct vm_operations_struct made up of several fields, the more interesting ones being:

struct vm_operations_struct {
        void (*open)(struct vm_area_struct * area);
        void (*close)(struct vm_area_struct * area);
        vm_fault_t (*fault)(struct vm_fault *vmf);
};

The open and close operations must update the GEM object reference count. Drivers can use the drm_gem_vm_open() and drm_gem_vm_close() helper functions directly as open and close handlers.

The fault operation handler is responsible for mapping individual pages to userspace when a page fault occurs. Depending on the memory allocation scheme, drivers can allocate pages at fault time, or can decide to allocate memory for the GEM object at the time the object is created.

Drivers that want to map the GEM object upfront instead of handling page faults can implement their own mmap file operation handler.

For platforms without MMU the GEM core provides a helper method drm_gem_dma_get_unmapped_area(). The mmap() routines will call this to get a proposed address for the mapping.

To use drm_gem_dma_get_unmapped_area(), drivers must fill the struct struct file_operations get_unmapped_area field with a pointer on drm_gem_dma_get_unmapped_area().

More detailed information about get_unmapped_area can be found in No-MMU memory mapping support

Memory Coherency¶

When mapped to the device or used in a command buffer, backing pages for an object are flushed to memory and marked write combined so as to be coherent with the GPU. Likewise, if the CPU accesses an object after the GPU has finished rendering to the object, then the object must be made coherent with the CPU's view of memory, usually involving GPU cache flushing of various kinds. This core CPU<->GPU coherency management is provided by a device-specific ioctl, which evaluates an object's current domain and performs any necessary flushing or synchronization to put the object into the desired coherency domain (note that the object may be busy, i.e. an active render target; in that case, setting the domain blocks the client and waits for rendering to complete before performing any necessary flushing operations).

Command Execution¶

Perhaps the most important GEM function for GPU devices is providing a command execution interface to clients. Client programs construct command buffers containing references to previously allocated memory objects, and then submit them to GEM. At that point, GEM takes care to bind all the objects into the GTT, execute the buffer, and provide necessary synchronization between clients accessing the same buffers. This often involves evicting some objects from the GTT and re-binding others (a fairly expensive operation), and providing relocation support which hides fixed GTT offsets from clients. Clients must take care not to submit command buffers that reference more objects than can fit in the GTT; otherwise, GEM will reject them and no rendering will occur. Similarly, if several objects in the buffer require fence registers to be allocated for correct rendering (e.g. 2D blits on pre-965 chips), care must be taken not to require more fence registers than are available to the client. Such resource management should be abstracted from the client in libdrm.

GEM Function Reference¶

enum drm_gem_object_status¶: bitmask of object state for fdinfo reporting

Constants

DRM_GEM_OBJECT_RESIDENT: object is resident in memory (ie. not unpinned)
DRM_GEM_OBJECT_PURGEABLE: object marked as purgeable by userspace

Description

Bitmask of status used for fdinfo memory stats, see drm_gem_object_funcs.status and drm_show_fdinfo(). Note that an object can DRM_GEM_OBJECT_PURGEABLE if it still active or not resident, in which case drm_show_fdinfo() will not account for it as purgeable. So drivers do not need to check if the buffer is idle and resident to return this bit. (Ie. userspace can mark a buffer as purgeable even while it is still busy on the GPU.. it does not _actually_ become puregeable until it becomes idle. The status gem object func does not need to consider this.)

struct drm_gem_object_funcs¶: GEM object functions

Definition:

struct drm_gem_object_funcs {
    void (*free)(struct drm_gem_object *obj);
    int (*open)(struct drm_gem_object *obj, struct drm_file *file);
    void (*close)(struct drm_gem_object *obj, struct drm_file *file);
    void (*print_info)(struct drm_printer *p, unsigned int indent, const struct drm_gem_object *obj);
    struct dma_buf *(*export)(struct drm_gem_object *obj, int flags);
    int (*pin)(struct drm_gem_object *obj);
    void (*unpin)(struct drm_gem_object *obj);
    struct sg_table *(*get_sg_table)(struct drm_gem_object *obj);
    int (*vmap)(struct drm_gem_object *obj, struct iosys_map *map);
    void (*vunmap)(struct drm_gem_object *obj, struct iosys_map *map);
    int (*mmap)(struct drm_gem_object *obj, struct vm_area_struct *vma);
    int (*evict)(struct drm_gem_object *obj);
    enum drm_gem_object_status (*status)(struct drm_gem_object *obj);
    const struct vm_operations_struct *vm_ops;
};

Members

free

Deconstructor for drm_gem_objects.

This callback is mandatory.

open

Called upon GEM handle creation.

This callback is optional.

close

Called upon GEM handle release.

This callback is optional.

print_info

If driver subclasses struct drm_gem_object, it can implement this optional hook for printing additional driver specific info.

drm_printf_indent() should be used in the callback passing it the indent argument.

This callback is called from drm_gem_print_info().

This callback is optional.

export

Export backing buffer as a dma_buf. If this is not set drm_gem_prime_export() is used.

This callback is optional.

pin

Pin backing buffer in memory. Used by the drm_gem_map_attach() helper.

This callback is optional.

unpin

Unpin backing buffer. Used by the drm_gem_map_detach() helper.

This callback is optional.

get_sg_table

Returns a Scatter-Gather table representation of the buffer. Used when exporting a buffer by the drm_gem_map_dma_buf() helper. Releasing is done by calling dma_unmap_sg_attrs() and sg_free_table() in drm_gem_unmap_buf(), therefore these helpers and this callback here cannot be used for sg tables pointing at driver private memory ranges.

GEM DMA Helper Functions Reference¶

The DRM GEM/DMA helpers are a means to provide buffer objects that are presented to the device as a contiguous chunk of memory. This is useful for devices that do not support scatter-gather DMA (either directly or by using an intimately attached IOMMU).

For devices that access the memory bus through an (external) IOMMU then the buffer objects are allocated using a traditional page-based allocator and may be scattered through physical memory. However they are contiguous in the IOVA space so appear contiguous to devices using them.

For other devices then the helpers rely on CMA to provide buffer objects that are physically contiguous in memory.

For GEM callback helpers in struct drm_gem_object functions, see likewise named functions with an _object_ infix (e.g., drm_gem_dma_object_vmap() wraps drm_gem_dma_vmap()). These helpers perform the necessary type conversion.

struct drm_gem_dma_object¶: GEM object backed by DMA memory allocations

Definition:

struct drm_gem_dma_object {
    struct drm_gem_object base;
    dma_addr_t dma_addr;
    struct sg_table *sgt;
    void *vaddr;
    bool map_noncoherent;
};

Members

base: base GEM object
dma_addr: DMA address of the backing memory
sgt: scatter/gather table for imported PRIME buffers. The table can have more than one entry but they are guaranteed to have contiguous DMA addresses.
vaddr: kernel virtual address of the backing memory
map_noncoherent: if true, the GEM object is backed by non-coherent memory

void drm_gem_dma_object_free(struct drm_gem_object *obj)¶: GEM object function for drm_gem_dma_free()

Parameters

struct drm_gem_object *obj: GEM object to free

Description

This function wraps drm_gem_dma_free_object(). Drivers that employ the DMA helpers should use it as their drm_gem_object_funcs.free handler.

void drm_gem_dma_object_print_info(struct drm_printer *p, unsigned int indent, const struct drm_gem_object *obj)¶: Print drm_gem_dma_object info for debugfs

Parameters

struct drm_printer *p: DRM printer
unsigned int indent: Tab indentation level
const struct drm_gem_object *obj: GEM object

Description

This function wraps drm_gem_dma_print_info(). Drivers that employ the DMA helpers should use this function as their drm_gem_object_funcs.print_info handler.

struct sg_table *drm_gem_dma_object_get_sg_table(struct drm_gem_object *obj)¶: GEM object function for drm_gem_dma_get_sg_table()

Parameters

struct drm_gem_object *obj: GEM object

Description

This function wraps drm_gem_dma_get_sg_table(). Drivers that employ the DMA helpers should use it as their drm_gem_object_funcs.get_sg_table handler.

Return

A pointer to the scatter/gather table of pinned pages or NULL on failure.

int drm_gem_dma_object_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)¶: GEM object function for drm_gem_dma_mmap()

Parameters

struct drm_gem_object *obj: GEM object
struct vm_area_struct *vma: VMA for the area to be mapped

Description

This function wraps drm_gem_dma_mmap(). Drivers that employ the dma helpers should use it as their drm_gem_object_funcs.mmap handler.

Return

0 on success or a negative error code on failure.

DRM_GEM_DMA_DRIVER_OPS_WITH_DUMB_CREATE¶

DRM_GEM_DMA_DRIVER_OPS_WITH_DUMB_CREATE (dumb_create_func)

DMA GEM driver operations

Parameters

dumb_create_func: callback function for .dumb_create

Description

This macro provides a shortcut for setting the default GEM operations in the drm_driver structure.

This macro is a variant of DRM_GEM_DMA_DRIVER_OPS for drivers that override the default implementation of struct rm_driver.dumb_create. Use DRM_GEM_DMA_DRIVER_OPS if possible. Drivers that require a virtual address on imported buffers should use DRM_GEM_DMA_DRIVER_OPS_VMAP_WITH_DUMB_CREATE() instead.

DRM_GEM_DMA_DRIVER_OPS¶

DRM_GEM_DMA_DRIVER_OPS ()

DMA GEM driver operations

Parameters

Description

This macro provides a shortcut for setting the default GEM operations in the drm_driver structure.

Drivers that come with their own implementation of struct drm_driver.dumb_create should use DRM_GEM_DMA_DRIVER_OPS_WITH_DUMB_CREATE() instead. Use DRM_GEM_DMA_DRIVER_OPS if possible. Drivers that require a virtual address on imported buffers should use DRM_GEM_DMA_DRIVER_OPS_VMAP instead.

DRM_GEM_DMA_DRIVER_OPS_VMAP_WITH_DUMB_CREATE¶

DRM_GEM_DMA_DRIVER_OPS_VMAP_WITH_DUMB_CREATE (dumb_create_func)

DMA GEM driver operations ensuring a virtual address on the buffer

Parameters

dumb_create_func: callback function for .dumb_create

Description

This macro provides a shortcut for setting the default GEM operations in the drm_driver structure for drivers that need the virtual address also on imported buffers.

This macro is a variant of DRM_GEM_DMA_DRIVER_OPS_VMAP for drivers that override the default implementation of struct drm_driver.dumb_create. Use DRM_GEM_DMA_DRIVER_OPS_VMAP if possible. Drivers that do not require a virtual address on imported buffers should use DRM_GEM_DMA_DRIVER_OPS_WITH_DUMB_CREATE() instead.

DRM_GEM_DMA_DRIVER_OPS_VMAP¶

DRM_GEM_DMA_DRIVER_OPS_VMAP ()

DMA GEM driver operations ensuring a virtual address on the buffer

Parameters

Description

This macro provides a shortcut for setting the default GEM operations in the drm_driver structure for drivers that need the virtual address also on imported buffers.

Drivers that come with their own implementation of struct drm_driver.dumb_create should use DRM_GEM_DMA_DRIVER_OPS_VMAP_WITH_DUMB_CREATE() instead. Use DRM_GEM_DMA_DRIVER_OPS_VMAP if possible. Drivers that do not require a virtual address on imported buffers should use DRM_GEM_DMA_DRIVER_OPS instead.

DEFINE_DRM_GEM_DMA_FOPS¶

DEFINE_DRM_GEM_DMA_FOPS (name)

macro to generate file operations for DMA drivers

Parameters

name: name for the generated structure

Description

This macro autogenerates a suitable struct file_operations for DMA based drivers, which can be assigned to drm_driver.fops. Note that this structure cannot be shared between drivers, because it contains a reference to the current module using THIS_MODULE.

Note that the declaration is already marked as static - if you need a non-static version of this you're probably doing it wrong and will break the THIS_MODULE reference by accident.

struct drm_gem_dma_object *drm_gem_dma_create(struct drm_device *drm, size_t size)¶: allocate an object with the given size

Parameters

struct drm_device *drm: DRM device
size_t size: size of the object to allocate

Description

This function creates a DMA GEM object and allocates memory as backing store. The allocated memory will occupy a contiguous chunk of bus address space.

For devices that are directly connected to the memory bus then the allocated memory will be physically contiguous. For devices that access through an IOMMU, then the allocated memory is not expected to be physically contiguous because having contiguous IOVAs is sufficient to meet a devices DMA requirements.

Return

A struct drm_gem_dma_object * on success or an ERR_PTR()-encoded negative error code on failure.

void drm_gem_dma_free(struct drm_gem_dma_object *dma_obj)¶: free resources associated with a DMA GEM object

Parameters

struct drm_gem_dma_object *dma_obj: DMA GEM object to free

Description

This function frees the backing memory of the DMA GEM object, cleans up the GEM object state and frees the memory used to store the object itself. If the buffer is imported and the virtual address is set, it is released.

int drm_gem_dma_dumb_create_internal(struct drm_file *file_priv, struct drm_device *drm, struct drm_mode_create_dumb *args)¶: create a dumb buffer object

Parameters

struct drm_file *file_priv: DRM file-private structure to create the dumb buffer for
struct drm_device *drm: DRM device
struct drm_mode_create_dumb *args: IOCTL data

Description

This aligns the pitch and size arguments to the minimum required. This is an internal helper that can be wrapped by a driver to account for hardware with more specific alignment requirements. It should not be used directly as their drm_driver.dumb_create callback.

Return

0 on success or a negative error code on failure.

int drm_gem_dma_dumb_create(struct drm_file *file_priv, struct drm_device *drm, struct drm_mode_create_dumb *args)¶: create a dumb buffer object

Parameters

struct drm_file *file_priv: DRM file-private structure to create the dumb buffer for
struct drm_device *drm: DRM device
struct drm_mode_create_dumb *args: IOCTL data

Description

This function computes the pitch of the dumb buffer and rounds it up to an integer number of bytes per pixel. Drivers for hardware that doesn't have any additional restrictions on the pitch can directly use this function as their drm_driver.dumb_create callback.

For hardware with additional restrictions, drivers can adjust the fields set up by userspace and pass the IOCTL data along to the drm_gem_dma_dumb_create_internal() function.

Return

0 on success or a negative error code on failure.

unsigned long drm_gem_dma_get_unmapped_area(struct file *filp, unsigned long addr, unsigned long len, unsigned long pgoff, unsigned long flags)¶: propose address for mapping in noMMU cases

Parameters

struct file *filp: file object
unsigned long addr: memory address
unsigned long len: buffer size
unsigned long pgoff: page offset
unsigned long flags: memory flags

Description

This function is used in noMMU platforms to propose address mapping for a given buffer. It's intended to be used as a direct handler for the struct file_operations.get_unmapped_area operation.

Return

mapping address on success or a negative error code on failure.

void drm_gem_dma_print_info(const struct drm_gem_dma_object *dma_obj, struct drm_printer *p, unsigned int indent)¶: Print drm_gem_dma_object info for debugfs

Parameters

const struct drm_gem_dma_object *dma_obj: DMA GEM object
struct drm_printer *p: DRM printer
unsigned int indent: Tab indentation level

Description

This function prints dma_addr and vaddr for use in e.g. debugfs output.

struct sg_table *drm_gem_dma_get_sg_table(struct drm_gem_dma_object *dma_obj)¶: provide a scatter/gather table of pinned pages for a DMA GEM object

Parameters

struct drm_gem_dma_object *dma_obj: DMA GEM object

Description

This function exports a scatter/gather table by calling the standard DMA mapping API.

Return

A pointer to the scatter/gather table of pinned pages or NULL on failure.

struct drm_gem_object *drm_gem_dma_prime_import_sg_table(struct drm_device *dev, struct dma_buf_attachment *attach, struct sg_table *sgt)¶: produce a DMA GEM object from another driver's scatter/gather table of pinned pages

Parameters

struct drm_device *dev: device to import into
struct dma_buf_attachment *attach: DMA-BUF attachment
struct sg_table *sgt: scatter/gather table of pinned pages

Description

This function imports a scatter/gather table exported via DMA-BUF by another driver. Imported buffers must be physically contiguous in memory (i.e. the scatter/gather table must contain a single entry). Drivers that use the DMA helpers should set this as their drm_driver.gem_prime_import_sg_table callback.

Return

A pointer to a newly created GEM object or an ERR_PTR-encoded negative error code on failure.

int drm_gem_dma_vmap(struct drm_gem_dma_object *dma_obj, struct iosys_map *map)¶: map a DMA GEM object into the kernel's virtual address space

Parameters

struct drm_gem_dma_object *dma_obj: DMA GEM object
struct iosys_map *map: Returns the kernel virtual address of the DMA GEM object's backing store.

Description

This function maps a buffer into the kernel's virtual address space. Since the DMA buffers are already mapped into the kernel virtual address space this simply returns the cached virtual address.

Return

0 on success, or a negative error code otherwise.

int drm_gem_dma_mmap(struct drm_gem_dma_object *dma_obj, struct vm_area_struct *vma)¶: memory-map an exported DMA GEM object

Parameters

struct drm_gem_dma_object *dma_obj: DMA GEM object
struct vm_area_struct *vma: VMA for the area to be mapped

Description

This function maps a buffer into a userspace process's address space. In addition to the usual GEM VMA setup it immediately faults in the entire object instead of using on-demand faulting.

Return

0 on success or a negative error code on failure.

struct drm_gem_object *drm_gem_dma_prime_import_sg_table_vmap(struct drm_device *dev, struct dma_buf_attachment *attach, struct sg_table *sgt)¶: PRIME import another driver's scatter/gather table and get the virtual address of the buffer

Parameters

struct drm_device *dev: DRM device
struct dma_buf_attachment *attach: DMA-BUF attachment
struct sg_table *sgt: Scatter/gather table of pinned pages

Description

This function imports a scatter/gather table using drm_gem_dma_prime_import_sg_table() and uses dma_buf_vmap() to get the kernel virtual address. This ensures that a DMA GEM object always has its virtual address set. This address is released when the object is freed.

This function can be used as the drm_driver.gem_prime_import_sg_table callback. The DRM_GEM_DMA_DRIVER_OPS_VMAP macro provides a shortcut to set the necessary DRM driver operations.

Return

A pointer to a newly created GEM object or an ERR_PTR-encoded negative error code on failure.

GEM SHMEM Helper Function Reference¶

This library provides helpers for GEM objects backed by shmem buffers allocated using anonymous pageable memory.

Functions that operate on the GEM object receive struct drm_gem_shmem_object. For GEM callback helpers in struct drm_gem_object functions, see likewise named functions with an _object_ infix (e.g., drm_gem_shmem_object_vmap() wraps drm_gem_shmem_vmap()). These helpers perform the necessary type conversion.

struct drm_gem_shmem_object¶: GEM object backed by shmem

Definition:

struct drm_gem_shmem_object {
    struct drm_gem_object base;
    struct page **pages;
    unsigned int pages_use_count;
    int madv;
    struct list_head madv_list;
    struct sg_table *sgt;
    void *vaddr;
    unsigned int vmap_use_count;
    bool pages_mark_dirty_on_put : 1;
    bool pages_mark_accessed_on_put : 1;
    bool map_wc : 1;
};

Members

base

Base GEM object

pages

Page table

pages_use_count

Reference count on the pages table. The pages are put when the count reaches zero.

madv

State for madvise

0 is active/inuse. A negative value is the object is purged. Positive values are driver specific and not used by the helpers.

madv_list

List entry for madvise tracking

Typically used by drivers to track purgeable objects

sgt

Scatter/gather table for imported PRIME buffers

vaddr

Kernel virtual address of the backing memory

vmap_use_count

Reference count on the virtual address. The address are un-mapped when the count reaches zero.

pages_mark_dirty_on_put

Mark pages as dirty when they are put.

pages_mark_accessed_on_put

Mark pages as accessed when they are put.

map_wc

map object write-combined (instead of using shmem defaults).

void drm_gem_shmem_object_free(struct drm_gem_object *obj)¶: GEM object function for drm_gem_shmem_free()

Parameters

struct drm_gem_object *obj: GEM object to free

Description

This function wraps drm_gem_shmem_free(). Drivers that employ the shmem helpers should use it as their drm_gem_object_funcs.free handler.

void drm_gem_shmem_object_print_info(struct drm_printer *p, unsigned int indent, const struct drm_gem_object *obj)¶: Print drm_gem_shmem_object info for debugfs

Parameters

struct drm_printer *p: DRM printer
unsigned int indent: Tab indentation level
const struct drm_gem_object *obj: GEM object

Description

This function wraps drm_gem_shmem_print_info(). Drivers that employ the shmem helpers should use this function as their drm_gem_object_funcs.print_info handler.

int drm_gem_shmem_object_pin(struct drm_gem_object *obj)¶: GEM object function for drm_gem_shmem_pin()

Parameters

struct drm_gem_object *obj: GEM object

Description

This function wraps drm_gem_shmem_pin(). Drivers that employ the shmem helpers should use it as their drm_gem_object_funcs.pin handler.

void drm_gem_shmem_object_unpin(struct drm_gem_object *obj)¶: GEM object function for drm_gem_shmem_unpin()

Parameters

struct drm_gem_object *obj: GEM object

Description

This function wraps drm_gem_shmem_unpin(). Drivers that employ the shmem helpers should use it as their drm_gem_object_funcs.unpin handler.

struct sg_table *drm_gem_shmem_object_get_sg_table(struct drm_gem_object *obj)¶: GEM object function for drm_gem_shmem_get_sg_table()

Parameters

struct drm_gem_object *obj: GEM object

Description

This function wraps drm_gem_shmem_get_sg_table(). Drivers that employ the shmem helpers should use it as their drm_gem_object_funcs.get_sg_table handler.

Return

A pointer to the scatter/gather table of pinned pages or error pointer on failure.

int drm_gem_shmem_object_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)¶: GEM object function for drm_gem_shmem_mmap()

Parameters

struct drm_gem_object *obj: GEM object
struct vm_area_struct *vma: VMA for the area to be mapped

Description

This function wraps drm_gem_shmem_mmap(). Drivers that employ the shmem helpers should use it as their drm_gem_object_funcs.mmap handler.

Return

0 on success or a negative error code on failure.

DRM_GEM_SHMEM_DRIVER_OPS¶

DRM_GEM_SHMEM_DRIVER_OPS ()

Default shmem GEM operations

Parameters

Description

This macro provides a shortcut for setting the shmem GEM operations in the drm_driver structure.

struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t size)¶: Allocate an object with the given size

Parameters

struct drm_device *dev: DRM device
size_t size: Size of the object to allocate

Description

This function creates a shmem GEM object.

Return

A struct drm_gem_shmem_object * on success or an ERR_PTR()-encoded negative error code on failure.

void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)¶: Free resources associated with a shmem GEM object

Parameters

struct drm_gem_shmem_object *shmem: shmem GEM object to free

Description

This function cleans up the GEM object state and frees the memory used to store the object itself.

int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem)¶: Pin backing pages for a shmem GEM object

Parameters

struct drm_gem_shmem_object *shmem: shmem GEM object

Description

This function makes sure the backing pages are pinned in memory while the buffer is exported.

Return

0 on success or a negative error code on failure.

void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)¶: Unpin backing pages for a shmem GEM object

Parameters

struct drm_gem_shmem_object *shmem: shmem GEM object

Description

This function removes the requirement that the backing pages are pinned in memory.

int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev, struct drm_mode_create_dumb *args)¶: Create a dumb shmem buffer object

Parameters

struct drm_file *file: DRM file structure to create the dumb buffer for
struct drm_device *dev: DRM device
struct drm_mode_create_dumb *args: IOCTL data

Description

This function computes the pitch of the dumb buffer and rounds it up to an integer number of bytes per pixel. Drivers for hardware that doesn't have any additional restrictions on the pitch can directly use this function as their drm_driver.dumb_create callback.

For hardware with additional restrictions, drivers can adjust the fields set up by userspace before calling into this function.

Return

0 on success or a negative error code on failure.

int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct *vma)¶: Memory-map a shmem GEM object

Parameters

struct drm_gem_shmem_object *shmem: shmem GEM object
struct vm_area_struct *vma: VMA for the area to be mapped

Description

This function implements an augmented version of the GEM DRM file mmap operation for shmem objects.

Return

0 on success or a negative error code on failure.

void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem, struct drm_printer *p, unsigned int indent)¶: Print drm_gem_shmem_object info for debugfs

Parameters

const struct drm_gem_shmem_object *shmem: shmem GEM object
struct drm_printer *p: DRM printer
unsigned int indent: Tab indentation level

struct sg_table *drm_gem_shmem_get_sg_table(struct drm_gem_shmem_object *shmem)¶: Provide a scatter/gather table of pinned pages for a shmem GEM object

Parameters

struct drm_gem_shmem_object *shmem: shmem GEM object

Description

This function exports a scatter/gather table suitable for PRIME usage by calling the standard DMA mapping API.

Drivers who need to acquire an scatter/gather table for objects need to call drm_gem_shmem_get_pages_sgt() instead.

Return

A pointer to the scatter/gather table of pinned pages or error pointer on failure.

struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_shmem_object *shmem)¶: Pin pages, dma map them, and return a scatter/gather table for a shmem GEM object.

Parameters

struct drm_gem_shmem_object *shmem: shmem GEM object

Description

This function returns a scatter/gather table suitable for driver usage. If the sg table doesn't exist, the pages are pinned, dma-mapped, and a sg table created.

This is the main function for drivers to get at backing storage, and it hides and difference between dma-buf imported and natively allocated objects. drm_gem_shmem_get_sg_table() should not be directly called by drivers.

Return

A pointer to the scatter/gather table of pinned pages or errno on failure.

struct drm_gem_object *drm_gem_shmem_prime_import_sg_table(struct drm_device *dev, struct dma_buf_attachment *attach, struct sg_table *sgt)¶: Produce a shmem GEM object from another driver's scatter/gather table of pinned pages

Parameters

struct drm_device *dev: Device to import into
struct dma_buf_attachment *attach: DMA-BUF attachment
struct sg_table *sgt: Scatter/gather table of pinned pages

Description

This function imports a scatter/gather table exported via DMA-BUF by another driver. Drivers that use the shmem helpers should set this as their drm_driver.gem_prime_import_sg_table callback.

Return

A pointer to a newly created GEM object or an ERR_PTR-encoded negative error code on failure.

GEM VRAM Helper Functions Reference¶

This library provides struct drm_gem_vram_object (GEM VRAM), a GEM buffer object that is backed by video RAM (VRAM). It can be used for framebuffer devices with dedicated memory.

The data structure struct drm_vram_mm and its helpers implement a memory manager for simple framebuffer devices with dedicated video memory. GEM VRAM buffer objects are either placed in the video memory or remain evicted to system memory.

With the GEM interface userspace applications create, manage and destroy graphics buffers, such as an on-screen framebuffer. GEM does not provide an implementation of these interfaces. It's up to the DRM driver to provide an implementation that suits the hardware. If the hardware device contains dedicated video memory, the DRM driver can use the VRAM helper library. Each active buffer object is stored in video RAM. Active buffer are used for drawing the current frame, typically something like the frame's scanout buffer or the cursor image. If there's no more space left in VRAM, inactive GEM objects can be moved to system memory.

To initialize the VRAM helper library call drmm_vram_helper_init(). The function allocates and initializes an instance of struct drm_vram_mm in struct drm_device.vram_mm . Use DRM_GEM_VRAM_DRIVER to initialize struct drm_driver and DRM_VRAM_MM_FILE_OPERATIONS to initialize struct file_operations; as illustrated below.

struct file_operations fops ={
        .owner = THIS_MODULE,
        DRM_VRAM_MM_FILE_OPERATION
};
struct drm_driver drv = {
        .driver_feature = DRM_ ... ,
        .fops = &fops,
        DRM_GEM_VRAM_DRIVER
};

int init_drm_driver()
{
        struct drm_device *dev;
        uint64_t vram_base;
        unsigned long vram_size;
        int ret;

        // setup device, vram base and size
        // ...

        ret = drmm_vram_helper_init(dev, vram_base, vram_size);
        if (ret)
                return ret;
        return 0;
}

This creates an instance of struct drm_vram_mm, exports DRM userspace interfaces for GEM buffer management and initializes file operations to allow for accessing created GEM buffers. With this setup, the DRM driver manages an area of video RAM with VRAM MM and provides GEM VRAM objects to userspace.

You don't have to clean up the instance of VRAM MM. drmm_vram_helper_init() is a managed interface that installs a clean-up handler to run during the DRM device's release.

For drawing or scanout operations, rsp. buffer objects have to be pinned in video RAM. Call drm_gem_vram_pin() with DRM_GEM_VRAM_PL_FLAG_VRAM or DRM_GEM_VRAM_PL_FLAG_SYSTEM to pin a buffer object in video RAM or system memory. Call drm_gem_vram_unpin() to release the pinned object afterwards.

A buffer object that is pinned in video RAM has a fixed address within that memory region. Call drm_gem_vram_offset() to retrieve this value. Typically it's used to program the hardware's scanout engine for framebuffers, set the cursor overlay's image for a mouse cursor, or use it as input to the hardware's drawing engine.

To access a buffer object's memory from the DRM driver, call drm_gem_vram_vmap(). It maps the buffer into kernel address space and returns the memory address. Use drm_gem_vram_vunmap() to release the mapping.

struct drm_gem_vram_object¶: GEM object backed by VRAM

Definition:

struct drm_gem_vram_object {
    struct ttm_buffer_object bo;
    struct iosys_map map;
    unsigned int vmap_use_count;
    struct ttm_placement placement;
    struct ttm_place placements[2];
};

Members

bo: TTM buffer object
map: Mapping information for bo
vmap_use_count: Reference count on the virtual address. The address are un-mapped when the count reaches zero.
placement: TTM placement information. Supported placements are TTM_PL_VRAM and TTM_PL_SYSTEM
placements: TTM placement information.

Description

The type struct drm_gem_vram_object represents a GEM object that is backed by VRAM. It can be used for simple framebuffer devices with dedicated memory. The buffer object can be evicted to system memory if video memory becomes scarce.

GEM VRAM objects perform reference counting for pin and mapping operations. So a buffer object that has been pinned N times with drm_gem_vram_pin() must be unpinned N times with drm_gem_vram_unpin(). The same applies to pairs of drm_gem_vram_kmap() and drm_gem_vram_kunmap(), as well as pairs of drm_gem_vram_vmap() and drm_gem_vram_vunmap().

struct drm_gem_vram_object *drm_gem_vram_of_bo(struct ttm_buffer_object *bo)¶: Returns the container of type struct drm_gem_vram_object for field bo.

Parameters

struct ttm_buffer_object *bo: the VRAM buffer object

Return

The containing GEM VRAM object

struct drm_gem_vram_object *drm_gem_vram_of_gem(struct drm_gem_object *gem)¶: Returns the container of type struct drm_gem_vram_object for field gem.

Parameters

struct drm_gem_object *gem: the GEM object

Return

The containing GEM VRAM object

DRM_GEM_VRAM_PLANE_HELPER_FUNCS¶

DRM_GEM_VRAM_PLANE_HELPER_FUNCS ()

Initializes struct drm_plane_helper_funcs for VRAM handling

Parameters

Description

Drivers may use GEM BOs as VRAM helpers for the framebuffer memory. This macro initializes struct drm_plane_helper_funcs to use the respective helper functions.

DRM_GEM_VRAM_DRIVER¶

DRM_GEM_VRAM_DRIVER ()

default callback functions for struct drm_driver

Parameters

Description

Drivers that use VRAM MM and GEM VRAM can use this macro to initialize struct drm_driver with default functions.

struct drm_vram_mm¶: An instance of VRAM MM

Definition:

struct drm_vram_mm {
    uint64_t vram_base;
    size_t vram_size;
    struct ttm_device bdev;
};

Members

vram_base: Base address of the managed video memory
vram_size: Size of the managed video memory in bytes
bdev: The TTM BO device.

Description

The fields struct drm_vram_mm.vram_base and struct drm_vram_mm.vrm_size are managed by VRAM MM, but are available for public read access. Use the field struct drm_vram_mm.bdev to access the TTM BO device.

struct drm_vram_mm *drm_vram_mm_of_bdev(struct ttm_device *bdev)¶: Returns the container of type struct ttm_device for field bdev.

Parameters

struct ttm_device *bdev: the TTM BO device

Return

The containing instance of struct drm_vram_mm

struct drm_gem_vram_object *drm_gem_vram_create(struct drm_device *dev, size_t size, unsigned long pg_align)¶: Creates a VRAM-backed GEM object

Parameters

struct drm_device *dev: the DRM device
size_t size: the buffer size in bytes
unsigned long pg_align: the buffer's alignment in multiples of the page size

Description

GEM objects are allocated by calling struct drm_driver.gem_create_object, if set. Otherwise kzalloc() will be used. Drivers can set their own GEM object functions in struct drm_driver.gem_create_object. If no functions are set, the new GEM object will use the default functions from GEM VRAM helpers.

Return

A new instance of struct drm_gem_vram_object on success, or an ERR_PTR()-encoded error code otherwise.

void drm_gem_vram_put(struct drm_gem_vram_object *gbo)¶: Releases a reference to a VRAM-backed GEM object

Parameters

struct drm_gem_vram_object *gbo: the GEM VRAM object

Description

See ttm_bo_put() for more information.

s64 drm_gem_vram_offset(struct drm_gem_vram_object *gbo)¶: Returns a GEM VRAM object's offset in video memory

Parameters

struct drm_gem_vram_object *gbo: the GEM VRAM object

Description

This function returns the buffer object's offset in the device's video memory. The buffer object has to be pinned to TTM_PL_VRAM.

Return

The buffer object's offset in video memory on success, or a negative errno code otherwise.

int drm_gem_vram_pin(struct drm_gem_vram_object *gbo, unsigned long pl_flag)¶: Pins a GEM VRAM object in a region.

Parameters

struct drm_gem_vram_object *gbo: the GEM VRAM object
unsigned long pl_flag: a bitmask of possible memory regions

Description

Pinning a buffer object ensures that it is not evicted from a memory region. A pinned buffer object has to be unpinned before it can be pinned to another region. If the pl_flag argument is 0, the buffer is pinned at its current location (video RAM or system memory).

Small buffer objects, such as cursor images, can lead to memory fragmentation if they are pinned in the middle of video RAM. This is especially a problem on devices with only a small amount of video RAM. Fragmentation can prevent the primary framebuffer from fitting in, even though there's enough memory overall. The modifier DRM_GEM_VRAM_PL_FLAG_TOPDOWN marks the buffer object to be pinned at the high end of the memory region to avoid fragmentation.

Return

0 on success, or a negative error code otherwise.

int drm_gem_vram_unpin(struct drm_gem_vram_object *gbo)¶: Unpins a GEM VRAM object

Parameters

struct drm_gem_vram_object *gbo: the GEM VRAM object

Return

0 on success, or a negative error code otherwise.

int drm_gem_vram_vmap(struct drm_gem_vram_object *gbo, struct iosys_map *map)¶: Pins and maps a GEM VRAM object into kernel address space

Parameters

struct drm_gem_vram_object *gbo: The GEM VRAM object to map
struct iosys_map *map: Returns the kernel virtual address of the VRAM GEM object's backing store.

Description

The vmap function pins a GEM VRAM object to its current location, either system or video memory, and maps its buffer into kernel address space. As pinned object cannot be relocated, you should avoid pinning objects permanently. Call drm_gem_vram_vunmap() with the returned address to unmap and unpin the GEM VRAM object.

Return

0 on success, or a negative error code otherwise.

void drm_gem_vram_vunmap(struct drm_gem_vram_object *gbo, struct iosys_map *map)¶: Unmaps and unpins a GEM VRAM object

Parameters

struct drm_gem_vram_object *gbo: The GEM VRAM object to unmap
struct iosys_map *map: Kernel virtual address where the VRAM GEM object was mapped

Description

A call to drm_gem_vram_vunmap() unmaps and unpins a GEM VRAM buffer. See the documentation for drm_gem_vram_vmap() for more information.

int drm_gem_vram_fill_create_dumb(struct drm_file *file, struct drm_device *dev, unsigned long pg_align, unsigned long pitch_align, struct drm_mode_create_dumb *args)¶: Helper for implementing struct drm_driver.dumb_create

Parameters

struct drm_file *file: the DRM file
struct drm_device *dev: the DRM device
unsigned long pg_align: the buffer's alignment in multiples of the page size
unsigned long pitch_align: the scanline's alignment in powers of 2
struct drm_mode_create_dumb *args: the arguments as provided to struct drm_driver.dumb_create

Description

This helper function fills struct drm_mode_create_dumb, which is used by struct drm_driver.dumb_create. Implementations of this interface should forwards their arguments to this helper, plus the driver-specific parameters.

Return

0 on success, or a negative error code otherwise.

int drm_gem_vram_driver_dumb_create(struct drm_file *file, struct drm_device *dev, struct drm_mode_create_dumb *args)¶: Implements struct drm_driver.dumb_create

Parameters

struct drm_file *file: the DRM file
struct drm_device *dev: the DRM device
struct drm_mode_create_dumb *args: the arguments as provided to struct drm_driver.dumb_create

Description

This function requires the driver to use drm_device.vram_mm for its instance of VRAM MM.

Return

0 on success, or a negative error code otherwise.

int drm_gem_vram_plane_helper_prepare_fb(struct drm_plane *plane, struct drm_plane_state *new_state)¶

Implements struct drm_plane_helper_funcs.prepare_fb

Parameters

struct drm_plane *plane: a DRM plane
struct drm_plane_state *new_state: the plane's new state

Description

During plane updates, this function sets the plane's fence and pins the GEM VRAM objects of the plane's new framebuffer to VRAM. Call drm_gem_vram_plane_helper_cleanup_fb() to unpin them.

Return

0 on success, or a negative errno code otherwise.

void drm_gem_vram_plane_helper_cleanup_fb(struct drm_plane *plane, struct drm_plane_state *old_state)¶

Implements struct drm_plane_helper_funcs.cleanup_fb

Parameters

struct drm_plane *plane: a DRM plane
struct drm_plane_state *old_state: the plane's old state

Description

During plane updates, this function unpins the GEM VRAM objects of the plane's old framebuffer from VRAM. Complements drm_gem_vram_plane_helper_prepare_fb().

int drm_gem_vram_simple_display_pipe_prepare_fb(struct drm_simple_display_pipe *pipe, struct drm_plane_state *new_state)¶

Implements struct drm_simple_display_pipe_funcs.prepare_fb

Parameters

struct drm_simple_display_pipe *pipe: a simple display pipe
struct drm_plane_state *new_state: the plane's new state

Description

During plane updates, this function pins the GEM VRAM objects of the plane's new framebuffer to VRAM. Call drm_gem_vram_simple_display_pipe_cleanup_fb() to unpin them.

Return

0 on success, or a negative errno code otherwise.

void drm_gem_vram_simple_display_pipe_cleanup_fb(struct drm_simple_display_pipe *pipe, struct drm_plane_state *old_state)¶

Implements struct drm_simple_display_pipe_funcs.cleanup_fb

Parameters

struct drm_simple_display_pipe *pipe: a simple display pipe
struct drm_plane_state *old_state: the plane's old state

Description

During plane updates, this function unpins the GEM VRAM objects of the plane's old framebuffer from VRAM. Complements drm_gem_vram_simple_display_pipe_prepare_fb().

void drm_vram_mm_debugfs_init(struct drm_minor *minor)¶: Register VRAM MM debugfs file.

Parameters

struct drm_minor *minor: drm minor device.

int drmm_vram_helper_init(struct drm_device *dev, uint64_t vram_base, size_t vram_size)¶: Initializes a device's instance of struct drm_vram_mm

Parameters

struct drm_device *dev: the DRM device
uint64_t vram_base: the base address of the video memory
size_t vram_size: the size of the video memory in bytes

Description

Creates a new instance of struct drm_vram_mm and stores it in struct drm_device.vram_mm. The instance is auto-managed and cleaned up as part of device cleanup. Calling this function multiple times will generate an error message.

Return

0 on success, or a negative errno code otherwise.

enum drm_mode_status drm_vram_helper_mode_valid(struct drm_device *dev, const struct drm_display_mode *mode)¶: Tests if a display mode's framebuffer fits into the available video memory.

Parameters

struct drm_device *dev: the DRM device
const struct drm_display_mode *mode: the mode to test

Description

This function tests if enough video memory is available for using the specified display mode. Atomic modesetting requires importing the designated framebuffer into video memory before evicting the active one. Hence, any framebuffer may consume at most half of the available VRAM. Display modes that require a larger framebuffer can not be used, even if the CRTC does support them. Each framebuffer is assumed to have 32-bit color depth.

Note

The function can only test if the display mode is supported in general. If there are too many framebuffers pinned to video memory, a display mode may still not be usable in practice. The color depth of 32-bit fits all current use case. A more flexible test can be added when necessary.

Return

MODE_OK if the display mode is supported, or an error code of type enum drm_mode_status otherwise.

GEM TTM Helper Functions Reference¶

This library provides helper functions for gem objects backed by ttm.

void drm_gem_ttm_print_info(struct drm_printer *p, unsigned int indent, const struct drm_gem_object *gem)¶: Print ttm_buffer_object info for debugfs

Parameters

struct drm_printer *p: DRM printer
unsigned int indent: Tab indentation level
const struct drm_gem_object *gem: GEM object

Description

This function can be used as drm_gem_object_funcs.print_info callback.

int drm_gem_ttm_vmap(struct drm_gem_object *gem, struct iosys_map *map)¶: vmap ttm_buffer_object

Parameters

struct drm_gem_object *gem: GEM object.
struct iosys_map *map: [out] returns the dma-buf mapping.

Description

Maps a GEM object with ttm_bo_vmap(). This function can be used as drm_gem_object_funcs.vmap callback.

Return

0 on success, or a negative errno code otherwise.

void drm_gem_ttm_vunmap(struct drm_gem_object *gem, struct iosys_map *map)¶: vunmap ttm_buffer_object

Parameters

struct drm_gem_object *gem: GEM object.
struct iosys_map *map: dma-buf mapping.

Description

Unmaps a GEM object with ttm_bo_vunmap(). This function can be used as drm_gem_object_funcs.vmap callback.

int drm_gem_ttm_mmap(struct drm_gem_object *gem, struct vm_area_struct *vma)¶: mmap ttm_buffer_object

Parameters

struct drm_gem_object *gem: GEM object.
struct vm_area_struct *vma: vm area.

Description

This function can be used as drm_gem_object_funcs.mmap callback.

int drm_gem_ttm_dumb_map_offset(struct drm_file *file, struct drm_device *dev, uint32_t handle, uint64_t *offset)¶: Implements struct drm_driver.dumb_map_offset

Parameters

struct drm_file *file: DRM file pointer.
struct drm_device *dev: DRM device.
uint32_t handle: GEM handle
uint64_t *offset: Returns the mapping's memory offset on success

Description

Provides an implementation of struct drm_driver.dumb_map_offset for TTM-based GEM drivers. TTM allocates the offset internally and drm_gem_ttm_dumb_map_offset() returns it for dumb-buffer implementations.

See struct drm_driver.dumb_map_offset.

Return

0 on success, or a negative errno code otherwise.

VMA Offset Manager¶

The vma-manager is responsible to map arbitrary driver-dependent memory regions into the linear user address-space. It provides offsets to the caller which can then be used on the address_space of the drm-device. It takes care to not overlap regions, size them appropriately and to not confuse mm-core by inconsistent fake vm_pgoff fields. Drivers shouldn't use this for object placement in VMEM. This manager should only be used to manage mappings into linear user-space VMs.

We use drm_mm as backend to manage object allocations. But it is highly optimized for alloc/free calls, not lookups. Hence, we use an rb-tree to speed up offset lookups.

You must not use multiple offset managers on a single address_space. Otherwise, mm-core will be unable to tear down memory mappings as the VM will no longer be linear.

This offset manager works on page-based addresses. That is, every argument and return code (with the exception of drm_vma_node_offset_addr()) is given in number of pages, not number of bytes. That means, object sizes and offsets must always be page-aligned (as usual). If you want to get a valid byte-based user-space address for a given offset, please see drm_vma_node_offset_addr().

Additionally to offset management, the vma offset manager also handles access management. For every open-file context that is allowed to access a given node, you must call drm_vma_node_allow(). Otherwise, an mmap() call on this open-file with the offset of the node will fail with -EACCES. To revoke access again, use drm_vma_node_revoke(). However, the caller is responsible for destroying already existing mappings, if required.

struct drm_vma_offset_node *drm_vma_offset_exact_lookup_locked(struct drm_vma_offset_manager *mgr, unsigned long start, unsigned long pages)¶: Look up node by exact address

Parameters

struct drm_vma_offset_manager *mgr: Manager object
unsigned long start: Start address (page-based, not byte-based)
unsigned long pages: Size of object (page-based)

Description

Same as drm_vma_offset_lookup_locked() but does not allow any offset into the node. It only returns the exact object with the given start address.

Return

Node at exact start address start.

void drm_vma_offset_lock_lookup(struct drm_vma_offset_manager *mgr)¶: Lock lookup for extended private use

Parameters

struct drm_vma_offset_manager *mgr: Manager object

Description

Lock VMA manager for extended lookups. Only locked VMA function calls are allowed while holding this lock. All other contexts are blocked from VMA until the lock is released via drm_vma_offset_unlock_lookup().

Use this if you need to take a reference to the objects returned by drm_vma_offset_lookup_locked() before releasing this lock again.

This lock must not be used for anything else than extended lookups. You must not call any other VMA helpers while holding this lock.

Note

You're in atomic-context while holding this lock!

void drm_vma_offset_unlock_lookup(struct drm_vma_offset_manager *mgr)¶: Unlock lookup for extended private use

Parameters

struct drm_vma_offset_manager *mgr: Manager object

Description

Release lookup-lock. See drm_vma_offset_lock_lookup() for more information.

void drm_vma_node_reset(struct drm_vma_offset_node *node)¶: Initialize or reset node object

Parameters

struct drm_vma_offset_node *node: Node to initialize or reset

Description

Reset a node to its initial state. This must be called before using it with any VMA offset manager.

This must not be called on an already allocated node, or you will leak memory.

unsigned long drm_vma_node_start(const struct drm_vma_offset_node *node)¶: Return start address for page-based addressing

Parameters

const struct drm_vma_offset_node *node: Node to inspect

Description

Return the start address of the given node. This can be used as offset into the linear VM space that is provided by the VMA offset manager. Note that this can only be used for page-based addressing. If you need a proper offset for user-space mappings, you must apply "<< PAGE_SHIFT" or use the drm_vma_node_offset_addr() helper instead.

Return

Start address of node for page-based addressing. 0 if the node does not have an offset allocated.

unsigned long drm_vma_node_size(struct drm_vma_offset_node *node)¶: Return size (page-based)

Parameters

struct drm_vma_offset_node *node: Node to inspect

Description

Return the size as number of pages for the given node. This is the same size that was passed to drm_vma_offset_add(). If no offset is allocated for the node, this is 0.

Return

Size of node as number of pages. 0 if the node does not have an offset allocated.

__u64 drm_vma_node_offset_addr(struct drm_vma_offset_node *node)¶: Return sanitized offset for user-space mmaps

Parameters

struct drm_vma_offset_node *node: Linked offset node

Description

Same as drm_vma_node_start() but returns the address as a valid offset that can be used for user-space mappings during mmap(). This must not be called on unlinked nodes.

Return

Offset of node for byte-based addressing. 0 if the node does not have an object allocated.

void drm_vma_node_unmap(struct drm_vma_offset_node *node, struct address_space *file_mapping)¶: Unmap offset node

Parameters

struct drm_vma_offset_node *node: Offset node
struct address_space *file_mapping: Address space to unmap node from

Description

Unmap all userspace mappings for a given offset node. The mappings must be associated with the file_mapping address-space. If no offset exists nothing is done.

This call is unlocked. The caller must guarantee that drm_vma_offset_remove() is not called on this node concurrently.

int drm_vma_node_verify_access(struct drm_vma_offset_node *node, struct drm_file *tag)¶: Access verification helper for TTM

Parameters

struct drm_vma_offset_node *node: Offset node
struct drm_file *tag: Tag of file to check

Description

This checks whether tag is granted access to node. It is the same as drm_vma_node_is_allowed() but suitable as drop-in helper for TTM verify_access() callbacks.

Return

0 if access is granted, -EACCES otherwise.

void drm_vma_offset_manager_init(struct drm_vma_offset_manager *mgr, unsigned long page_offset, unsigned long size)¶: Initialize new offset-manager

Parameters

struct drm_vma_offset_manager *mgr: Manager object
unsigned long page_offset: Offset of available memory area (page-based)
unsigned long size: Size of available address space range (page-based)

Description

Initialize a new offset-manager. The offset and area size available for the manager are given as page_offset and size. Both are interpreted as page-numbers, not bytes.

Adding/removing nodes from the manager is locked internally and protected against concurrent access. However, node allocation and destruction is left for the caller. While calling into the vma-manager, a given node must always be guaranteed to be referenced.

void drm_vma_offset_manager_destroy(struct drm_vma_offset_manager *mgr)¶: Destroy offset manager

Parameters

struct drm_vma_offset_manager *mgr: Manager object

Description

Destroy an object manager which was previously created via drm_vma_offset_manager_init(). The caller must remove all allocated nodes before destroying the manager. Otherwise, drm_mm will refuse to free the requested resources.

The manager must not be accessed after this function is called.

struct drm_vma_offset_node *drm_vma_offset_lookup_locked(struct drm_vma_offset_manager *mgr, unsigned long start, unsigned long pages)¶: Find node in offset space

Parameters

struct drm_vma_offset_manager *mgr: Manager object
unsigned long start: Start address for object (page-based)
unsigned long pages: Size of object (page-based)

Description

Find a node given a start address and object size. This returns the _best_ match for the given node. That is, start may point somewhere into a valid region and the given node will be returned, as long as the node spans the whole requested area (given the size in number of pages as pages).

Note that before lookup the vma offset manager lookup lock must be acquired with drm_vma_offset_lock_lookup(). See there for an example. This can then be used to implement weakly referenced lookups using kref_get_unless_zero().

drm_vma_offset_lock_lookup(mgr);
node = drm_vma_offset_lookup_locked(mgr);
if (node)
    kref_get_unless_zero(container_of(node, sth, entr));
drm_vma_offset_unlock_lookup(mgr);

Example

Return

Returns NULL if no suitable node can be found. Otherwise, the best match is returned. It's the caller's responsibility to make sure the node doesn't get destroyed before the caller can access it.

int drm_vma_offset_add(struct drm_vma_offset_manager *mgr, struct drm_vma_offset_node *node, unsigned long pages)¶: Add offset node to manager

Parameters

struct drm_vma_offset_manager *mgr: Manager object
struct drm_vma_offset_node *node: Node to be added
unsigned long pages: Allocation size visible to user-space (in number of pages)

Description

Add a node to the offset-manager. If the node was already added, this does nothing and return 0. pages is the size of the object given in number of pages. After this call succeeds, you can access the offset of the node until it is removed again.

If this call fails, it is safe to retry the operation or call drm_vma_offset_remove(), anyway. However, no cleanup is required in that case.

pages is not required to be the same size as the underlying memory object that you want to map. It only limits the size that user-space can map into their address space.

Return

0 on success, negative error code on failure.

void drm_vma_offset_remove(struct drm_vma_offset_manager *mgr, struct drm_vma_offset_node *node)¶: Remove offset node from manager

Parameters

struct drm_vma_offset_manager *mgr: Manager object
struct drm_vma_offset_node *node: Node to be removed

Description

Remove a node from the offset manager. If the node wasn't added before, this does nothing. After this call returns, the offset and size will be 0 until a new offset is allocated via drm_vma_offset_add() again. Helper functions like drm_vma_node_start() and drm_vma_node_offset_addr() will return 0 if no offset is allocated.

int drm_vma_node_allow(struct drm_vma_offset_node *node, struct drm_file *tag)¶: Add open-file to list of allowed users

Parameters

struct drm_vma_offset_node *node: Node to modify
struct drm_file *tag: Tag of file to remove

Description

Add tag to the list of allowed open-files for this node. If tag is already on this list, the ref-count is incremented.

The list of allowed-users is preserved across drm_vma_offset_add() and drm_vma_offset_remove() calls. You may even call it if the node is currently not added to any offset-manager.

You must remove all open-files the same number of times as you added them before destroying the node. Otherwise, you will leak memory.

This is locked against concurrent access internally.

Return

0 on success, negative error code on internal failure (out-of-mem)

int drm_vma_node_allow_once(struct drm_vma_offset_node *node, struct drm_file *tag)¶: Add open-file to list of allowed users

Parameters

struct drm_vma_offset_node *node: Node to modify
struct drm_file *tag: Tag of file to remove

Description

Add tag to the list of allowed open-files for this node.

The list of allowed-users is preserved across drm_vma_offset_add() and drm_vma_offset_remove() calls. You may even call it if the node is currently not added to any offset-manager.

This is not ref-counted unlike drm_vma_node_allow() hence drm_vma_node_revoke() should only be called once after this.

This is locked against concurrent access internally.

Return

0 on success, negative error code on internal failure (out-of-mem)

void drm_vma_node_revoke(struct drm_vma_offset_node *node, struct drm_file *tag)¶: Remove open-file from list of allowed users

Parameters

struct drm_vma_offset_node *node: Node to modify
struct drm_file *tag: Tag of file to remove

Description

Decrement the ref-count of tag in the list of allowed open-files on node. If the ref-count drops to zero, remove tag from the list. You must call this once for every drm_vma_node_allow() on tag.

This is locked against concurrent access internally.

If tag is not on the list, nothing is done.

bool drm_vma_node_is_allowed(struct drm_vma_offset_node *node, struct drm_file *tag)¶: Check whether an open-file is granted access

Parameters

struct drm_vma_offset_node *node: Node to check
struct drm_file *tag: Tag of file to remove

Description

Search the list in node whether tag is currently on the list of allowed open-files (see drm_vma_node_allow()).

This is locked against concurrent access internally.

Return

true if filp is on the list

DRM MM Range Allocator¶

Overview¶

drm_mm provides a simple range allocator. The drivers are free to use the resource allocator from the linux core if it suits them, the upside of drm_mm is that it's in the DRM core. Which means that it's easier to extend for some of the crazier special purpose needs of gpus.

The main data struct is drm_mm, allocations are tracked in drm_mm_node. Drivers are free to embed either of them into their own suitable datastructures. drm_mm itself will not do any memory allocations of its own, so if drivers choose not to embed nodes they need to still allocate them themselves.

The range allocator also supports reservation of preallocated blocks. This is useful for taking over initial mode setting configurations from the firmware, where an object needs to be created which exactly matches the firmware's scanout target. As long as the range is still free it can be inserted anytime after the allocator is initialized, which helps with avoiding looped dependencies in the driver load sequence.

drm_mm maintains a stack of most recently freed holes, which of all simplistic datastructures seems to be a fairly decent approach to clustering allocations and avoiding too much fragmentation. This means free space searches are O(num_holes). Given that all the fancy features drm_mm supports something better would be fairly complex and since gfx thrashing is a fairly steep cliff not a real concern. Removing a node again is O(1).

drm_mm supports a few features: Alignment and range restrictions can be supplied. Furthermore every drm_mm_node has a color value (which is just an opaque unsigned long) which in conjunction with a driver callback can be used to implement sophisticated placement restrictions. The i915 DRM driver uses this to implement guard pages between incompatible caching domains in the graphics TT.

Two behaviors are supported for searching and allocating: bottom-up and top-down. The default is bottom-up. Top-down allocation can be used if the memory area has different restrictions, or just to reduce fragmentation.

Finally iteration helpers to walk all nodes and all holes are provided as are some basic allocator dumpers for debugging.

Note that this range allocator is not thread-safe, drivers need to protect modifications with their own locking. The idea behind this is that for a full memory manager additional data needs to be protected anyway, hence internal locking would be fully redundant.

LRU Scan/Eviction Support¶

Very often GPUs need to have continuous allocations for a given object. When evicting objects to make space for a new one it is therefore not most efficient when we simply start to select all objects from the tail of an LRU until there's a suitable hole: Especially for big objects or nodes that otherwise have special allocation constraints there's a good chance we evict lots of (smaller) objects unnecessarily.

The DRM range allocator supports this use-case through the scanning interfaces. First a scan operation needs to be initialized with drm_mm_scan_init() or drm_mm_scan_init_with_range(). The driver adds objects to the roster, probably by walking an LRU list, but this can be freely implemented. Eviction candidates are added using drm_mm_scan_add_block() until a suitable hole is found or there are no further evictable objects. Eviction roster metadata is tracked in struct drm_mm_scan.

The driver must walk through all objects again in exactly the reverse order to restore the allocator state. Note that while the allocator is used in the scan mode no other operation is allowed.

Finally the driver evicts all objects selected (drm_mm_scan_remove_block() reported true) in the scan, and any overlapping nodes after color adjustment (drm_mm_scan_color_evict()). Adding and removing an object is O(1), and since freeing a node is also O(1) the overall complexity is O(scanned_objects). So like the free stack which needs to be walked before a scan operation even begins this is linear in the number of objects. It doesn't seem to hurt too badly.

DRM MM Range Allocator Function References¶

enum drm_mm_insert_mode¶: control search and allocation behaviour

Constants

DRM_MM_INSERT_BEST

Search for the smallest hole (within the search range) that fits the desired node.

Allocates the node from the bottom of the found hole.

DRM_MM_INSERT_LOW

Search for the lowest hole (address closest to 0, within the search range) that fits the desired node.

Allocates the node from the bottom of the found hole.

DRM_MM_INSERT_HIGH

Search for the highest hole (address closest to U64_MAX, within the search range) that fits the desired node.

Allocates the node from the top of the found hole. The specified alignment for the node is applied to the base of the node (drm_mm_node.start).

DRM_MM_INSERT_EVICT

Search for the most recently evicted hole (within the search range) that fits the desired node. This is appropriate for use immediately after performing an eviction scan (see drm_mm_scan_init()) and removing the selected nodes to form a hole.

Allocates the node from the bottom of the found hole.

DRM_MM_INSERT_ONCE

Only check the first hole for suitablity and report -ENOSPC immediately otherwise, rather than check every hole until a suitable one is found. Can only be used in conjunction with another search method such as DRM_MM_INSERT_HIGH or DRM_MM_INSERT_LOW.

DRM_MM_INSERT_HIGHEST

Only check the highest hole (the hole with the largest address) and insert the node at the top of the hole or report -ENOSPC if unsuitable.

Does not search all holes.

DRM_MM_INSERT_LOWEST

Only check the lowest hole (the hole with the smallest address) and insert the node at the bottom of the hole or report -ENOSPC if unsuitable.

Does not search all holes.

Description

The struct drm_mm range manager supports finding a suitable modes using a number of search trees. These trees are oranised by size, by address and in most recent eviction order. This allows the user to find either the smallest hole to reuse, the lowest or highest address to reuse, or simply reuse the most recent eviction that fits. When allocating the drm_mm_node from within the hole, the drm_mm_insert_mode also dictate whether to allocate the lowest matching address or the highest.

struct drm_mm_node¶: allocated block in the DRM allocator

Definition:

struct drm_mm_node {
    unsigned long color;
    u64 start;
    u64 size;
};

Members

color: Opaque driver-private tag.
start: Start address of the allocated block.
size: Size of the allocated block.

Description

This represents an allocated block in a drm_mm allocator. Except for pre-reserved nodes inserted using drm_mm_reserve_node() the structure is entirely opaque and should only be accessed through the provided funcions. Since allocation of these nodes is entirely handled by the driver they can be embedded.

struct drm_mm¶: DRM allocator

Definition:

struct drm_mm {
    void (*color_adjust)(const struct drm_mm_node *node,unsigned long color, u64 *start, u64 *end);
};

Members

color_adjust: Optional driver callback to further apply restrictions on a hole. The node argument points at the node containing the hole from which the block would be allocated (see drm_mm_hole_follows() and friends). The other arguments are the size of the block to be allocated. The driver can adjust the start and end as needed to e.g. insert guard pages.

Description

DRM range allocator with a few special functions and features geared towards managing GPU memory. Except for the color_adjust callback the structure is entirely opaque and should only be accessed through the provided functions and macros. This structure can be embedded into larger driver structures.

struct drm_mm_scan¶: DRM allocator eviction roaster data

Definition:

struct drm_mm_scan {
};

Members

Description

This structure tracks data needed for the eviction roaster set up using drm_mm_scan_init(), and used with drm_mm_scan_add_block() and drm_mm_scan_remove_block(). The structure is entirely opaque and should only be accessed through the provided functions and macros. It is meant to be allocated temporarily by the driver on the stack.

bool drm_mm_node_allocated(const struct drm_mm_node *node)¶: checks whether a node is allocated

Parameters

const struct drm_mm_node *node: drm_mm_node to check

Description

Drivers are required to clear a node prior to using it with the drm_mm range manager.

Drivers should use this helper for proper encapsulation of drm_mm internals.

Return

True if the node is allocated.

bool drm_mm_initialized(const struct drm_mm *mm)¶: checks whether an allocator is initialized

Parameters

const struct drm_mm *mm: drm_mm to check

Description

Drivers should clear the struct drm_mm prior to initialisation if they want to use this function.

Drivers should use this helper for proper encapsulation of drm_mm internals.

Return

True if the mm is initialized.

bool drm_mm_hole_follows(const struct drm_mm_node *node)¶: checks whether a hole follows this node

Parameters

const struct drm_mm_node *node: drm_mm_node to check

Description

Holes are embedded into the drm_mm using the tail of a drm_mm_node. If you wish to know whether a hole follows this particular node, query this function. See also drm_mm_hole_node_start() and drm_mm_hole_node_end().

Return

True if a hole follows the node.

u64 drm_mm_hole_node_start(const struct drm_mm_node *hole_node)¶: computes the start of the hole following node

Parameters

const struct drm_mm_node *hole_node: drm_mm_node which implicitly tracks the following hole

Description

This is useful for driver-specific debug dumpers. Otherwise drivers should not inspect holes themselves. Drivers must check first whether a hole indeed follows by looking at drm_mm_hole_follows()

Return

Start of the subsequent hole.

u64 drm_mm_hole_node_end(const struct drm_mm_node *hole_node)¶: computes the end of the hole following node

Parameters

const struct drm_mm_node *hole_node: drm_mm_node which implicitly tracks the following hole

Description

This is useful for driver-specific debug dumpers. Otherwise drivers should not inspect holes themselves. Drivers must check first whether a hole indeed follows by looking at drm_mm_hole_follows().

Return

End of the subsequent hole.

drm_mm_nodes¶

drm_mm_nodes (mm)

list of nodes under the drm_mm range manager

Parameters

mm: the struct drm_mm range manager

Description

As the drm_mm range manager hides its node_list deep with its structure, extracting it looks painful and repetitive. This is not expected to be used outside of the drm_mm_for_each_node() macros and similar internal functions.

Return

The node list, may be empty.

drm_mm_for_each_node¶

drm_mm_for_each_node (entry, mm)

iterator to walk over all allocated nodes

Parameters

entry: struct drm_mm_node to assign to in each iteration step
mm: drm_mm allocator to walk

Description

This iterator walks over all nodes in the range allocator. It is implemented with list_for_each(), so not save against removal of elements.

drm_mm_for_each_node_safe¶

drm_mm_for_each_node_safe (entry, next, mm)

iterator to walk over all allocated nodes

Parameters

entry: struct drm_mm_node to assign to in each iteration step
next: struct drm_mm_node to store the next step
mm: drm_mm allocator to walk

Description

This iterator walks over all nodes in the range allocator. It is implemented with list_for_each_safe(), so save against removal of elements.

drm_mm_for_each_hole¶

drm_mm_for_each_hole (pos, mm, hole_start, hole_end)

iterator to walk over all holes

Parameters

pos: drm_mm_node used internally to track progress
mm: drm_mm allocator to walk
hole_start: ulong variable to assign the hole start to on each iteration
hole_end: ulong variable to assign the hole end to on each iteration

Description

This iterator walks over all holes in the range allocator. It is implemented with list_for_each(), so not save against removal of elements. entry is used internally and will not reflect a real drm_mm_node for the very first hole. Hence users of this iterator may not access it.

Implementation Note: We need to inline list_for_each_entry in order to be able to set hole_start and hole_end on each iteration while keeping the macro sane.

int drm_mm_insert_node_generic(struct drm_mm *mm, struct drm_mm_node *node, u64 size, u64 alignment, unsigned long color, enum drm_mm_insert_mode mode)¶: search for space and insert node

Parameters

struct drm_mm *mm: drm_mm to allocate from
struct drm_mm_node *node: preallocate node to insert
u64 size: size of the allocation
u64 alignment: alignment of the allocation
unsigned long color: opaque tag value to use for this node
enum drm_mm_insert_mode mode: fine-tune the allocation search and placement

Description

This is a simplified version of drm_mm_insert_node_in_range() with no range restrictions applied.

The preallocated node must be cleared to 0.

Return

0 on success, -ENOSPC if there's no suitable hole.

int drm_mm_insert_node(struct drm_mm *mm, struct drm_mm_node *node, u64 size)¶: search for space and insert node

Parameters

struct drm_mm *mm: drm_mm to allocate from
struct drm_mm_node *node: preallocate node to insert
u64 size: size of the allocation

Description

This is a simplified version of drm_mm_insert_node_generic() with color set to 0.

The preallocated node must be cleared to 0.

Return

0 on success, -ENOSPC if there's no suitable hole.

bool drm_mm_clean(const struct drm_mm *mm)¶: checks whether an allocator is clean

Parameters

const struct drm_mm *mm: drm_mm allocator to check

Return

True if the allocator is completely free, false if there's still a node allocated in it.

drm_mm_for_each_node_in_range¶

drm_mm_for_each_node_in_range (node__, mm__, start__, end__)

iterator to walk over a range of allocated nodes

Parameters

node__: drm_mm_node structure to assign to in each iteration step
mm__: drm_mm allocator to walk
start__: starting offset, the first node will overlap this
end__: ending offset, the last node will start before this (but may overlap)

Description

This iterator walks over all nodes in the range allocator that lie between start and end. It is implemented similarly to list_for_each(), but using the internal interval tree to accelerate the search for the starting node, and so not safe against removal of elements. It assumes that end is within (or is the upper limit of) the drm_mm allocator. If [start, end] are beyond the range of the drm_mm, the iterator may walk over the special _unallocated_ drm_mm.head_node, and may even continue indefinitely.

void drm_mm_scan_init(struct drm_mm_scan *scan, struct drm_mm *mm, u64 size, u64 alignment, unsigned long color, enum drm_mm_insert_mode mode)¶: initialize lru scanning

Parameters

struct drm_mm_scan *scan: scan state
struct drm_mm *mm: drm_mm to scan
u64 size: size of the allocation
u64 alignment: alignment of the allocation
unsigned long color: opaque tag value to use for the allocation
enum drm_mm_insert_mode mode: fine-tune the allocation search and placement

Description

This is a simplified version of drm_mm_scan_init_with_range() with no range restrictions applied.

This simply sets up the scanning routines with the parameters for the desired hole.

Warning: As long as the scan list is non-empty, no other operations than adding/removing nodes to/from the scan list are allowed.

int drm_mm_reserve_node(struct drm_mm *mm, struct drm_mm_node *node)¶: insert an pre-initialized node

Parameters

struct drm_mm *mm: drm_mm allocator to insert node into
struct drm_mm_node *node: drm_mm_node to insert

Description

This functions inserts an already set-up drm_mm_node into the allocator, meaning that start, size and color must be set by the caller. All other fields must be cleared to 0. This is useful to initialize the allocator with preallocated objects which must be set-up before the range allocator can be set-up, e.g. when taking over a firmware framebuffer.

Return

0 on success, -ENOSPC if there's no hole where node is.

int drm_mm_insert_node_in_range(struct drm_mm *const mm, struct drm_mm_node *const node, u64 size, u64 alignment, unsigned long color, u64 range_start, u64 range_end, enum drm_mm_insert_mode mode)¶: ranged search for space and insert node

Parameters

struct drm_mm * const mm: drm_mm to allocate from
struct drm_mm_node * const node: preallocate node to insert
u64 size: size of the allocation
u64 alignment: alignment of the allocation
unsigned long color: opaque tag value to use for this node
u64 range_start: start of the allowed range for this node
u64 range_end: end of the allowed range for this node
enum drm_mm_insert_mode mode: fine-tune the allocation search and placement

Description

The preallocated node must be cleared to 0.

Return

0 on success, -ENOSPC if there's no suitable hole.

void drm_mm_remove_node(struct drm_mm_node *node)¶: Remove a memory node from the allocator.

Parameters

struct drm_mm_node *node: drm_mm_node to remove

Description

This just removes a node from its drm_mm allocator. The node does not need to be cleared again before it can be re-inserted into this or any other drm_mm allocator. It is a bug to call this function on a unallocated node.

void drm_mm_replace_node(struct drm_mm_node *old, struct drm_mm_node *new)¶: move an allocation from old to new

Parameters

struct drm_mm_node *old: drm_mm_node to remove from the allocator
struct drm_mm_node *new: drm_mm_node which should inherit old's allocation

Description

This is useful for when drivers embed the drm_mm_node structure and hence can't move allocations by reassigning pointers. It's a combination of remove and insert with the guarantee that the allocation start will match.

void drm_mm_scan_init_with_range(struct drm_mm_scan *scan, struct drm_mm *mm, u64 size, u64 alignment, unsigned long color, u64 start, u64 end, enum drm_mm_insert_mode mode)¶: initialize range-restricted lru scanning

Parameters

struct drm_mm_scan *scan: scan state
struct drm_mm *mm: drm_mm to scan
u64 size: size of the allocation
u64 alignment: alignment of the allocation
unsigned long color: opaque tag value to use for the allocation
u64 start: start of the allowed range for the allocation
u64 end: end of the allowed range for the allocation
enum drm_mm_insert_mode mode: fine-tune the allocation search and placement

Description

This simply sets up the scanning routines with the parameters for the desired hole.

Warning: As long as the scan list is non-empty, no other operations than adding/removing nodes to/from the scan list are allowed.

bool drm_mm_scan_add_block(struct drm_mm_scan *scan, struct drm_mm_node *node)¶: add a node to the scan list

Parameters

struct drm_mm_scan *scan: the active drm_mm scanner
struct drm_mm_node *node: drm_mm_node to add

Description

Add a node to the scan list that might be freed to make space for the desired hole.

Return

True if a hole has been found, false otherwise.

bool drm_mm_scan_remove_block(struct drm_mm_scan *scan, struct drm_mm_node *node)¶: remove a node from the scan list

Parameters

struct drm_mm_scan *scan: the active drm_mm scanner
struct drm_mm_node *node: drm_mm_node to remove

Description

Nodes must be removed in exactly the reverse order from the scan list as they have been added (e.g. using list_add() as they are added and then list_for_each() over that eviction list to remove), otherwise the internal state of the memory manager will be corrupted.

When the scan list is empty, the selected memory nodes can be freed. An immediately following drm_mm_insert_node_in_range_generic() or one of the simpler versions of that function with !DRM_MM_SEARCH_BEST will then return the just freed block (because it's at the top of the free_stack list).

Return

True if this block should be evicted, false otherwise. Will always return false when no hole has been found.

struct drm_mm_node *drm_mm_scan_color_evict(struct drm_mm_scan *scan)¶: evict overlapping nodes on either side of hole

Parameters

struct drm_mm_scan *scan: drm_mm scan with target hole

Description

After completing an eviction scan and removing the selected nodes, we may need to remove a few more nodes from either side of the target hole if mm.color_adjust is being used.

Return

A node to evict, or NULL if there are no overlapping nodes.

void drm_mm_init(struct drm_mm *mm, u64 start, u64 size)¶: initialize a drm-mm allocator

Parameters

struct drm_mm *mm: the drm_mm structure to initialize
u64 start: start of the range managed by mm
u64 size: end of the range managed by mm

Description

Note that mm must be cleared to 0 before calling this function.

void drm_mm_takedown(struct drm_mm *mm)¶: clean up a drm_mm allocator

Parameters

struct drm_mm *mm: drm_mm allocator to clean up

Description

Note that it is a bug to call this function on an allocator which is not clean.

void drm_mm_print(const struct drm_mm *mm, struct drm_printer *p)¶: print allocator state

Parameters

const struct drm_mm *mm: drm_mm allocator to print
struct drm_printer *p: DRM printer to use

DRM GPU VA Manager¶

Overview¶

The DRM GPU VA Manager, represented by struct drm_gpuva_manager keeps track of a GPU's virtual address (VA) space and manages the corresponding virtual mappings represented by drm_gpuva objects. It also keeps track of the mapping's backing drm_gem_object buffers.

drm_gem_object buffers maintain a list of drm_gpuva objects representing all existent GPU VA mappings using this drm_gem_object as backing buffer.

GPU VAs can be flagged as sparse, such that drivers may use GPU VAs to also keep track of sparse PTEs in order to support Vulkan 'Sparse Resources'.

The GPU VA manager internally uses a rb-tree to manage the drm_gpuva mappings within a GPU's virtual address space.

The drm_gpuva_manager contains a special drm_gpuva representing the portion of VA space reserved by the kernel. This node is initialized together with the GPU VA manager instance and removed when the GPU VA manager is destroyed.

In a typical application drivers would embed struct drm_gpuva_manager and struct drm_gpuva within their own driver specific structures, there won't be any memory allocations of its own nor memory allocations of drm_gpuva entries.

The data structures needed to store drm_gpuvas within the drm_gpuva_manager are contained within struct drm_gpuva already. Hence, for inserting drm_gpuva entries from within dma-fence signalling critical sections it is enough to pre-allocate the drm_gpuva structures.

Split and Merge¶

Besides its capability to manage and represent a GPU VA space, the drm_gpuva_manager also provides functions to let the drm_gpuva_manager calculate a sequence of operations to satisfy a given map or unmap request.

Therefore the DRM GPU VA manager provides an algorithm implementing splitting and merging of existent GPU VA mappings with the ones that are requested to be mapped or unmapped. This feature is required by the Vulkan API to implement Vulkan 'Sparse Memory Bindings' - drivers UAPIs often refer to this as VM BIND.

Drivers can call drm_gpuva_sm_map() to receive a sequence of callbacks containing map, unmap and remap operations for a given newly requested mapping. The sequence of callbacks represents the set of operations to execute in order to integrate the new mapping cleanly into the current state of the GPU VA space.

Depending on how the new GPU VA mapping intersects with the existent mappings of the GPU VA space the drm_gpuva_fn_ops callbacks contain an arbitrary amount of unmap operations, a maximum of two remap operations and a single map operation. The caller might receive no callback at all if no operation is required, e.g. if the requested mapping already exists in the exact same way.

The single map operation represents the original map operation requested by the caller.

drm_gpuva_op_unmap contains a 'keep' field, which indicates whether the drm_gpuva to unmap is physically contiguous with the original mapping request. Optionally, if 'keep' is set, drivers may keep the actual page table entries for this drm_gpuva, adding the missing page table entries only and update the drm_gpuva_manager's view of things accordingly.

Drivers may do the same optimization, namely delta page table updates, also for remap operations. This is possible since drm_gpuva_op_remap consists of one unmap operation and one or two map operations, such that drivers can derive the page table update delta accordingly.

Note that there can't be more than two existent mappings to split up, one at the beginning and one at the end of the new mapping, hence there is a maximum of two remap operations.

Analogous to drm_gpuva_sm_map() drm_gpuva_sm_unmap() uses drm_gpuva_fn_ops to call back into the driver in order to unmap a range of GPU VA space. The logic behind this function is way simpler though: For all existent mappings enclosed by the given range unmap operations are created. For mappings which are only partically located within the given range, remap operations are created such that those mappings are split up and re-mapped partically.

As an alternative to drm_gpuva_sm_map() and drm_gpuva_sm_unmap(), drm_gpuva_sm_map_ops_create() and drm_gpuva_sm_unmap_ops_create() can be used to directly obtain an instance of struct drm_gpuva_ops containing a list of drm_gpuva_op, which can be iterated with drm_gpuva_for_each_op(). This list contains the drm_gpuva_ops analogous to the callbacks one would receive when calling drm_gpuva_sm_map() or drm_gpuva_sm_unmap(). While this way requires more memory (to allocate the drm_gpuva_ops), it provides drivers a way to iterate the drm_gpuva_op multiple times, e.g. once in a context where memory allocations are possible (e.g. to allocate GPU page tables) and once in the dma-fence signalling critical path.

To update the drm_gpuva_manager's view of the GPU VA space drm_gpuva_insert() and drm_gpuva_remove() may be used. These functions can safely be used from drm_gpuva_fn_ops callbacks originating from drm_gpuva_sm_map() or drm_gpuva_sm_unmap(). However, it might be more convenient to use the provided helper functions drm_gpuva_map(), drm_gpuva_remap() and drm_gpuva_unmap() instead.

The following diagram depicts the basic relationships of existent GPU VA mappings, a newly requested mapping and the resulting mappings as implemented by drm_gpuva_sm_map() - it doesn't cover any arbitrary combinations of these.

Requested mapping is identical. Replace it, but indicate the backing PTEs could be kept.

     0     a     1
old: |-----------| (bo_offset=n)

     0     a     1
req: |-----------| (bo_offset=n)

     0     a     1
new: |-----------| (bo_offset=n)

Requested mapping is identical, except for the BO offset, hence replace the mapping.

     0     a     1
old: |-----------| (bo_offset=n)

     0     a     1
req: |-----------| (bo_offset=m)

     0     a     1
new: |-----------| (bo_offset=m)

Requested mapping is identical, except for the backing BO, hence replace the mapping.

     0     a     1
old: |-----------| (bo_offset=n)

     0     b     1
req: |-----------| (bo_offset=n)

     0     b     1
new: |-----------| (bo_offset=n)

Existent mapping is a left aligned subset of the requested one, hence replace the existent one.
```
     0  a  1
old: |-----|       (bo_offset=n)

     0     a     2
req: |-----------| (bo_offset=n)

     0     a     2
new: |-----------| (bo_offset=n)
```
Note

We expect to see the same result for a request with a different BO and/or non-contiguous BO offset.
Requested mapping's range is a left aligned subset of the existent one, but backed by a different BO. Hence, map the requested mapping and split the existent one adjusting its BO offset.
```
     0     a     2
old: |-----------| (bo_offset=n)

     0  b  1
req: |-----|       (bo_offset=n)

     0  b  1  a' 2
new: |-----|-----| (b.bo_offset=n, a.bo_offset=n+1)
```
Note

We expect to see the same result for a request with a different BO and/or non-contiguous BO offset.

Existent mapping is a superset of the requested mapping. Split it up, but indicate that the backing PTEs could be kept.

     0     a     2
old: |-----------| (bo_offset=n)

     0  a  1
req: |-----|       (bo_offset=n)

     0  a  1  a' 2
new: |-----|-----| (a.bo_offset=n, a'.bo_offset=n+1)

Requested mapping's range is a right aligned subset of the existent one, but backed by a different BO. Hence, map the requested mapping and split the existent one, without adjusting the BO offset.
```
     0     a     2
old: |-----------| (bo_offset=n)

           1  b  2
req:       |-----| (bo_offset=m)

     0  a  1  b  2
new: |-----|-----| (a.bo_offset=n,b.bo_offset=m)
```

Existent mapping is a superset of the requested mapping. Split it up, but indicate that the backing PTEs could be kept.

      0     a     2
old: |-----------| (bo_offset=n)

           1  a  2
req:       |-----| (bo_offset=n+1)

     0  a' 1  a  2
new: |-----|-----| (a'.bo_offset=n, a.bo_offset=n+1)

Existent mapping is overlapped at the end by the requested mapping backed by a different BO. Hence, map the requested mapping and split up the existent one, without adjusting the BO offset.

     0     a     2
old: |-----------|       (bo_offset=n)

           1     b     3
req:       |-----------| (bo_offset=m)

     0  a  1     b     3
new: |-----|-----------| (a.bo_offset=n,b.bo_offset=m)

Existent mapping is overlapped by the requested mapping, both having the same backing BO with a contiguous offset. Indicate the backing PTEs of the old mapping could be kept.

     0     a     2
old: |-----------|       (bo_offset=n)

           1     a     3
req:       |-----------| (bo_offset=n+1)

     0  a' 1     a     3
new: |-----|-----------| (a'.bo_offset=n, a.bo_offset=n+1)

Requested mapping's range is a centered subset of the existent one having a different backing BO. Hence, map the requested mapping and split up the existent one in two mappings, adjusting the BO offset of the right one accordingly.
```
     0        a        3
old: |-----------------| (bo_offset=n)

           1  b  2
req:       |-----|       (bo_offset=m)

     0  a  1  b  2  a' 3
new: |-----|-----|-----| (a.bo_offset=n,b.bo_offset=m,a'.bo_offset=n+2)
```

Requested mapping is a contiguous subset of the existent one. Split it up, but indicate that the backing PTEs could be kept.

     0        a        3
old: |-----------------| (bo_offset=n)

           1  a  2
req:       |-----|       (bo_offset=n+1)

     0  a' 1  a  2 a'' 3
old: |-----|-----|-----| (a'.bo_offset=n, a.bo_offset=n+1, a''.bo_offset=n+2)

Existent mapping is a right aligned subset of the requested one, hence replace the existent one.
```
           1  a  2
old:       |-----| (bo_offset=n+1)

     0     a     2
req: |-----------| (bo_offset=n)

     0     a     2
new: |-----------| (bo_offset=n)
```
Note

We expect to see the same result for a request with a different bo and/or non-contiguous bo_offset.
Existent mapping is a centered subset of the requested one, hence replace the existent one.
```
           1  a  2
old:       |-----| (bo_offset=n+1)

     0        a       3
req: |----------------| (bo_offset=n)

     0        a       3
new: |----------------| (bo_offset=n)
```
Note

We expect to see the same result for a request with a different bo and/or non-contiguous bo_offset.

Existent mappings is overlapped at the beginning by the requested mapping backed by a different BO. Hence, map the requested mapping and split up the existent one, adjusting its BO offset accordingly.

           1     a     3
old:       |-----------| (bo_offset=n)

     0     b     2
req: |-----------|       (bo_offset=m)

     0     b     2  a' 3
new: |-----------|-----| (b.bo_offset=m,a.bo_offset=n+2)

Locking¶

Generally, the GPU VA manager does not take care of locking itself, it is the drivers responsibility to take care about locking. Drivers might want to protect the following operations: inserting, removing and iterating drm_gpuva objects as well as generating all kinds of operations, such as split / merge or prefetch.

The GPU VA manager also does not take care of the locking of the backing drm_gem_object buffers GPU VA lists by itself; drivers are responsible to enforce mutual exclusion using either the GEMs dma_resv lock or alternatively a driver specific external lock. For the latter see also drm_gem_gpuva_set_lock().

However, the GPU VA manager contains lockdep checks to ensure callers of its API hold the corresponding lock whenever the drm_gem_objects GPU VA list is accessed by functions such as drm_gpuva_link() or drm_gpuva_unlink().

Examples¶

This section gives two examples on how to let the DRM GPUVA Manager generate drm_gpuva_op in order to satisfy a given map or unmap request and how to make use of them.

The below code is strictly limited to illustrate the generic usage pattern. To maintain simplicitly, it doesn't make use of any abstractions for common code, different (asyncronous) stages with fence signalling critical paths, any other helpers or error handling in terms of freeing memory and dropping previously taken locks.

Obtain a list of drm_gpuva_op to create a new mapping:

// Allocates a new &drm_gpuva.
struct drm_gpuva * driver_gpuva_alloc(void);

// Typically drivers would embedd the &drm_gpuva_manager and &drm_gpuva
// structure in individual driver structures and lock the dma-resv with
// drm_exec or similar helpers.
int driver_mapping_create(struct drm_gpuva_manager *mgr,
                          u64 addr, u64 range,
                          struct drm_gem_object *obj, u64 offset)
{
        struct drm_gpuva_ops *ops;
        struct drm_gpuva_op *op

        driver_lock_va_space();
        ops = drm_gpuva_sm_map_ops_create(mgr, addr, range,
                                          obj, offset);
        if (IS_ERR(ops))
                return PTR_ERR(ops);

        drm_gpuva_for_each_op(op, ops) {
                struct drm_gpuva *va;

                switch (op->op) {
                case DRM_GPUVA_OP_MAP:
                        va = driver_gpuva_alloc();
                        if (!va)
                                ; // unwind previous VA space updates,
                                  // free memory and unlock

                        driver_vm_map();
                        drm_gpuva_map(mgr, va, &op->map);
                        drm_gpuva_link(va);

                        break;
                case DRM_GPUVA_OP_REMAP: {
                        struct drm_gpuva *prev = NULL, *next = NULL;

                        va = op->remap.unmap->va;

                        if (op->remap.prev) {
                                prev = driver_gpuva_alloc();
                                if (!prev)
                                        ; // unwind previous VA space
                                          // updates, free memory and
                                          // unlock
                        }

                        if (op->remap.next) {
                                next = driver_gpuva_alloc();
                                if (!next)
                                        ; // unwind previous VA space
                                          // updates, free memory and
                                          // unlock
                        }

                        driver_vm_remap();
                        drm_gpuva_remap(prev, next, &op->remap);

                        drm_gpuva_unlink(va);
                        if (prev)
                                drm_gpuva_link(prev);
                        if (next)
                                drm_gpuva_link(next);

                        break;
                }
                case DRM_GPUVA_OP_UNMAP:
                        va = op->unmap->va;

                        driver_vm_unmap();
                        drm_gpuva_unlink(va);
                        drm_gpuva_unmap(&op->unmap);

                        break;
                default:
                        break;
                }
        }
        driver_unlock_va_space();

        return 0;
}

Receive a callback for each drm_gpuva_op to create a new mapping:

struct driver_context {
        struct drm_gpuva_manager *mgr;
        struct drm_gpuva *new_va;
        struct drm_gpuva *prev_va;
        struct drm_gpuva *next_va;
};

// ops to pass to drm_gpuva_manager_init()
static const struct drm_gpuva_fn_ops driver_gpuva_ops = {
        .sm_step_map = driver_gpuva_map,
        .sm_step_remap = driver_gpuva_remap,
        .sm_step_unmap = driver_gpuva_unmap,
};

// Typically drivers would embedd the &drm_gpuva_manager and &drm_gpuva
// structure in individual driver structures and lock the dma-resv with
// drm_exec or similar helpers.
int driver_mapping_create(struct drm_gpuva_manager *mgr,
                          u64 addr, u64 range,
                          struct drm_gem_object *obj, u64 offset)
{
        struct driver_context ctx;
        struct drm_gpuva_ops *ops;
        struct drm_gpuva_op *op;
        int ret = 0;

        ctx.mgr = mgr;

        ctx.new_va = kzalloc(sizeof(*ctx.new_va), GFP_KERNEL);
        ctx.prev_va = kzalloc(sizeof(*ctx.prev_va), GFP_KERNEL);
        ctx.next_va = kzalloc(sizeof(*ctx.next_va), GFP_KERNEL);
        if (!ctx.new_va || !ctx.prev_va || !ctx.next_va) {
                ret = -ENOMEM;
                goto out;
        }

        driver_lock_va_space();
        ret = drm_gpuva_sm_map(mgr, &ctx, addr, range, obj, offset);
        driver_unlock_va_space();

out:
        kfree(ctx.new_va);
        kfree(ctx.prev_va);
        kfree(ctx.next_va);
        return ret;
}

int driver_gpuva_map(struct drm_gpuva_op *op, void *__ctx)
{
        struct driver_context *ctx = __ctx;

        drm_gpuva_map(ctx->mgr, ctx->new_va, &op->map);

        drm_gpuva_link(ctx->new_va);

        // prevent the new GPUVA from being freed in
        // driver_mapping_create()
        ctx->new_va = NULL;

        return 0;
}

int driver_gpuva_remap(struct drm_gpuva_op *op, void *__ctx)
{
        struct driver_context *ctx = __ctx;

        drm_gpuva_remap(ctx->prev_va, ctx->next_va, &op->remap);

        drm_gpuva_unlink(op->remap.unmap->va);
        kfree(op->remap.unmap->va);

        if (op->remap.prev) {
                drm_gpuva_link(ctx->prev_va);
                ctx->prev_va = NULL;
        }

        if (op->remap.next) {
                drm_gpuva_link(ctx->next_va);
                ctx->next_va = NULL;
        }

        return 0;
}

int driver_gpuva_unmap(struct drm_gpuva_op *op, void *__ctx)
{
        drm_gpuva_unlink(op->unmap.va);
        drm_gpuva_unmap(&op->unmap);
        kfree(op->unmap.va);

        return 0;
}

DRM GPU VA Manager Function References¶

enum drm_gpuva_flags¶: flags for struct drm_gpuva

Constants

DRM_GPUVA_INVALIDATED: Flag indicating that the drm_gpuva's backing GEM is invalidated.
DRM_GPUVA_SPARSE: Flag indicating that the drm_gpuva is a sparse mapping.
DRM_GPUVA_USERBITS: user defined bits

struct drm_gpuva¶: structure to track a GPU VA mapping

Definition:

struct drm_gpuva {
    struct drm_gpuva_manager *mgr;
    enum drm_gpuva_flags flags;
    struct {
        u64 addr;
        u64 range;
    } va;
    struct {
        u64 offset;
        struct drm_gem_object *obj;
        struct list_head entry;
    } gem;
    struct {
        struct rb_node node;
        struct list_head entry;
        u64 __subtree_last;
    } rb;
};

Members

mgr: the drm_gpuva_manager this object is associated with
flags: the drm_gpuva_flags for this mapping
va: structure containing the address and range of the drm_gpuva
gem: structure containing the drm_gem_object and it's offset
rb: the rb-tree node

Description

This structure represents a GPU VA mapping and is associated with a drm_gpuva_manager.

Typically, this structure is embedded in bigger driver structures.

void drm_gpuva_invalidate(struct drm_gpuva *va, bool invalidate)¶: sets whether the backing GEM of this drm_gpuva is invalidated

Parameters

struct drm_gpuva *va: the drm_gpuva to set the invalidate flag for
bool invalidate: indicates whether the drm_gpuva is invalidated

bool drm_gpuva_invalidated(struct drm_gpuva *va)¶: indicates whether the backing BO of this drm_gpuva is invalidated

Parameters

struct drm_gpuva *va: the drm_gpuva to check

struct drm_gpuva_manager¶: DRM GPU VA Manager

Definition:

struct drm_gpuva_manager {
    const char *name;
    u64 mm_start;
    u64 mm_range;
    struct {
        struct rb_root_cached tree;
        struct list_head list;
    } rb;
    struct drm_gpuva kernel_alloc_node;
    const struct drm_gpuva_fn_ops *ops;
};

Members

name: the name of the DRM GPU VA space
mm_start: start of the VA space
mm_range: length of the VA space
rb: structures to track drm_gpuva entries
kernel_alloc_node: drm_gpuva representing the address space cutout reserved for the kernel
ops: drm_gpuva_fn_ops providing the split/merge steps to drivers

Description

The DRM GPU VA Manager keeps track of a GPU's virtual address space by using maple_tree structures. Typically, this structure is embedded in bigger driver structures.

Drivers can pass addresses and ranges in an arbitrary unit, e.g. bytes or pages.

There should be one manager instance per GPU virtual address space.

drm_gpuva_for_each_va_range¶

drm_gpuva_for_each_va_range (va__, mgr__, start__, end__)

iterate over a range of drm_gpuvas

Parameters

va__: drm_gpuva structure to assign to in each iteration step
mgr__: drm_gpuva_manager to walk over
start__: starting offset, the first gpuva will overlap this
end__: ending offset, the last gpuva will start before this (but may overlap)

Description

This iterator walks over all drm_gpuvas in the drm_gpuva_manager that lie between start__ and end__. It is implemented similarly to list_for_each(), but is using the drm_gpuva_manager's internal interval tree to accelerate the search for the starting drm_gpuva, and hence isn't safe against removal of elements. It assumes that end__ is within (or is the upper limit of) the drm_gpuva_manager. This iterator does not skip over the drm_gpuva_manager's kernel_alloc_node.

drm_gpuva_for_each_va_range_safe¶

drm_gpuva_for_each_va_range_safe (va__, next__, mgr__, start__, end__)

safely iterate over a range of drm_gpuvas

Parameters

va__: drm_gpuva to assign to in each iteration step
next__: another drm_gpuva to use as temporary storage
mgr__: drm_gpuva_manager to walk over
start__: starting offset, the first gpuva will overlap this
end__: ending offset, the last gpuva will start before this (but may overlap)

Description

This iterator walks over all drm_gpuvas in the drm_gpuva_manager that lie between start__ and end__. It is implemented similarly to list_for_each_safe(), but is using the drm_gpuva_manager's internal interval tree to accelerate the search for the starting drm_gpuva, and hence is safe against removal of elements. It assumes that end__ is within (or is the upper limit of) the drm_gpuva_manager. This iterator does not skip over the drm_gpuva_manager's kernel_alloc_node.

drm_gpuva_for_each_va¶

drm_gpuva_for_each_va (va__, mgr__)

iterate over all drm_gpuvas

Parameters

va__: drm_gpuva to assign to in each iteration step
mgr__: drm_gpuva_manager to walk over

Description

This iterator walks over all drm_gpuva structures associated with the given drm_gpuva_manager.

drm_gpuva_for_each_va_safe¶

drm_gpuva_for_each_va_safe (va__, next__, mgr__)

safely iterate over all drm_gpuvas

Parameters

va__: drm_gpuva to assign to in each iteration step
next__: another drm_gpuva to use as temporary storage
mgr__: drm_gpuva_manager to walk over

Description

This iterator walks over all drm_gpuva structures associated with the given drm_gpuva_manager. It is implemented with list_for_each_entry_safe(), and hence safe against the removal of elements.

enum drm_gpuva_op_type¶: GPU VA operation type

Constants

DRM_GPUVA_OP_MAP: the map op type
DRM_GPUVA_OP_REMAP: the remap op type
DRM_GPUVA_OP_UNMAP: the unmap op type
DRM_GPUVA_OP_PREFETCH: the prefetch op type

Description

Operations to alter the GPU VA mappings tracked by the drm_gpuva_manager.

struct drm_gpuva_op_map¶: GPU VA map operation

Definition:

struct drm_gpuva_op_map {
    struct {
        u64 addr;
        u64 range;
    } va;
    struct {
        u64 offset;
        struct drm_gem_object *obj;
    } gem;
};

Members

va: structure containing address and range of a map operation
gem: structure containing the drm_gem_object and it's offset

Description

This structure represents a single map operation generated by the DRM GPU VA manager.

struct drm_gpuva_op_unmap¶: GPU VA unmap operation

Definition:

struct drm_gpuva_op_unmap {
    struct drm_gpuva *va;
    bool keep;
};

Members

va

the drm_gpuva to unmap

keep

Indicates whether this drm_gpuva is physically contiguous with the original mapping request.

Optionally, if keep is set, drivers may keep the actual page table mappings for this drm_gpuva, adding the missing page table entries only and update the drm_gpuva_manager accordingly.

Description

This structure represents a single unmap operation generated by the DRM GPU VA manager.

struct drm_gpuva_op_remap¶: GPU VA remap operation

Definition:

struct drm_gpuva_op_remap {
    struct drm_gpuva_op_map *prev;
    struct drm_gpuva_op_map *next;
    struct drm_gpuva_op_unmap *unmap;
};

Members

prev: the preceding part of a split mapping
next: the subsequent part of a split mapping
unmap: the unmap operation for the original existing mapping

Description

This represents a single remap operation generated by the DRM GPU VA manager.

A remap operation is generated when an existing GPU VA mmapping is split up by inserting a new GPU VA mapping or by partially unmapping existent mapping(s), hence it consists of a maximum of two map and one unmap operation.

The unmap operation takes care of removing the original existing mapping. prev is used to remap the preceding part, next the subsequent part.

If either a new mapping's start address is aligned with the start address of the old mapping or the new mapping's end address is aligned with the end address of the old mapping, either prev or next is NULL.

Note, the reason for a dedicated remap operation, rather than arbitrary unmap and map operations, is to give drivers the chance of extracting driver specific data for creating the new mappings from the unmap operations's drm_gpuva structure which typically is embedded in larger driver specific structures.

struct drm_gpuva_op_prefetch¶: GPU VA prefetch operation

Definition:

struct drm_gpuva_op_prefetch {
    struct drm_gpuva *va;
};

Members

va: the drm_gpuva to prefetch

Description

This structure represents a single prefetch operation generated by the DRM GPU VA manager.

struct drm_gpuva_op¶: GPU VA operation

Definition:

struct drm_gpuva_op {
    struct list_head entry;
    enum drm_gpuva_op_type op;
    union {
        struct drm_gpuva_op_map map;
        struct drm_gpuva_op_remap remap;
        struct drm_gpuva_op_unmap unmap;
        struct drm_gpuva_op_prefetch prefetch;
    };
};

Members

entry: The list_head used to distribute instances of this struct within drm_gpuva_ops.
op: the type of the operation
{unnamed_union}: anonymous
map: the map operation
remap: the remap operation
unmap: the unmap operation
prefetch: the prefetch operation

Description

This structure represents a single generic operation.

The particular type of the operation is defined by op.

struct drm_gpuva_ops¶: wraps a list of drm_gpuva_op

Definition:

struct drm_gpuva_ops {
    struct list_head list;
};

Members

list: the list_head

drm_gpuva_for_each_op¶

drm_gpuva_for_each_op (op, ops)

iterator to walk over drm_gpuva_ops

Parameters

op: drm_gpuva_op to assign in each iteration step
ops: drm_gpuva_ops to walk

Description

This iterator walks over all ops within a given list of operations.

drm_gpuva_for_each_op_safe¶

drm_gpuva_for_each_op_safe (op, next, ops)

iterator to safely walk over drm_gpuva_ops

Parameters

op: drm_gpuva_op to assign in each iteration step
next: next drm_gpuva_op to store the next step
ops: drm_gpuva_ops to walk

Description

This iterator walks over all ops within a given list of operations. It is implemented with list_for_each_safe(), so save against removal of elements.

drm_gpuva_for_each_op_from_reverse¶

drm_gpuva_for_each_op_from_reverse (op, ops)

iterate backwards from the given point

Parameters

op: drm_gpuva_op to assign in each iteration step
ops: drm_gpuva_ops to walk

Description

This iterator walks over all ops within a given list of operations beginning from the given operation in reverse order.

drm_gpuva_first_op¶

drm_gpuva_first_op (ops)

returns the first drm_gpuva_op from drm_gpuva_ops

Parameters

ops: the drm_gpuva_ops to get the fist drm_gpuva_op from

drm_gpuva_last_op¶

drm_gpuva_last_op (ops)

returns the last drm_gpuva_op from drm_gpuva_ops

Parameters

ops: the drm_gpuva_ops to get the last drm_gpuva_op from

drm_gpuva_prev_op¶

drm_gpuva_prev_op (op)

previous drm_gpuva_op in the list

Parameters

op: the current drm_gpuva_op

drm_gpuva_next_op¶

drm_gpuva_next_op (op)

next drm_gpuva_op in the list

Parameters

op: the current drm_gpuva_op

struct drm_gpuva_fn_ops¶: callbacks for split/merge steps

Definition:

struct drm_gpuva_fn_ops {
    struct drm_gpuva_op *(*op_alloc)(void);
    void (*op_free)(struct drm_gpuva_op *op);
    int (*sm_step_map)(struct drm_gpuva_op *op, void *priv);
    int (*sm_step_remap)(struct drm_gpuva_op *op, void *priv);
    int (*sm_step_unmap)(struct drm_gpuva_op *op, void *priv);
};

Members

op_alloc

called when the drm_gpuva_manager allocates a struct drm_gpuva_op

Some drivers may want to embed struct drm_gpuva_op into driver specific structures. By implementing this callback drivers can allocate memory accordingly.

This callback is optional.

op_free

called when the drm_gpuva_manager frees a struct drm_gpuva_op

Some drivers may want to embed struct drm_gpuva_op into driver specific structures. By implementing this callback drivers can free the previously allocated memory accordingly.

This callback is optional.

sm_step_map

called from drm_gpuva_sm_map to finally insert the mapping once all previous steps were completed

The priv pointer matches the one the driver passed to drm_gpuva_sm_map or drm_gpuva_sm_unmap, respectively.

Can be NULL if drm_gpuva_sm_map is used.

sm_step_remap

called from drm_gpuva_sm_map and drm_gpuva_sm_unmap to split up an existent mapping

This callback is called when existent mapping needs to be split up. This is the case when either a newly requested mapping overlaps or is enclosed by an existent mapping or a partial unmap of an existent mapping is requested.

The priv pointer matches the one the driver passed to drm_gpuva_sm_map or drm_gpuva_sm_unmap, respectively.

Can be NULL if neither drm_gpuva_sm_map nor drm_gpuva_sm_unmap is used.

sm_step_unmap

called from drm_gpuva_sm_map and drm_gpuva_sm_unmap to unmap an existent mapping

This callback is called when existent mapping needs to be unmapped. This is the case when either a newly requested mapping encloses an existent mapping or an unmap of an existent mapping is requested.

The priv pointer matches the one the driver passed to drm_gpuva_sm_map or drm_gpuva_sm_unmap, respectively.

Can be NULL if neither drm_gpuva_sm_map nor drm_gpuva_sm_unmap is used.

Description

This structure defines the callbacks used by drm_gpuva_sm_map and drm_gpuva_sm_unmap to provide the split/merge steps for map and unmap operations to drivers.

void drm_gpuva_manager_init(struct drm_gpuva_manager *mgr, const char *name, u64 start_offset, u64 range, u64 reserve_offset, u64 reserve_range, const struct drm_gpuva_fn_ops *ops)¶: initialize a drm_gpuva_manager

Parameters

struct drm_gpuva_manager *mgr: pointer to the drm_gpuva_manager to initialize
const char *name: the name of the GPU VA space
u64 start_offset: the start offset of the GPU VA space
u64 range: the size of the GPU VA space
u64 reserve_offset: the start of the kernel reserved GPU VA area
u64 reserve_range: the size of the kernel reserved GPU VA area
const struct drm_gpuva_fn_ops *ops: drm_gpuva_fn_ops called on drm_gpuva_sm_map / drm_gpuva_sm_unmap

Description

The drm_gpuva_manager must be initialized with this function before use.

Note that mgr must be cleared to 0 before calling this function. The given name is expected to be managed by the surrounding driver structures.

void drm_gpuva_manager_destroy(struct drm_gpuva_manager *mgr)¶: cleanup a drm_gpuva_manager

Parameters

struct drm_gpuva_manager *mgr: pointer to the drm_gpuva_manager to clean up

Description

Note that it is a bug to call this function on a manager that still holds GPU VA mappings.

int drm_gpuva_insert(struct drm_gpuva_manager *mgr, struct drm_gpuva *va)¶: insert a drm_gpuva

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager to insert the drm_gpuva in
struct drm_gpuva *va: the drm_gpuva to insert

Description

Insert a drm_gpuva with a given address and range into a drm_gpuva_manager.

It is safe to use this function using the safe versions of iterating the GPU VA space, such as drm_gpuva_for_each_va_safe() and drm_gpuva_for_each_va_range_safe().

Return

0 on success, negative error code on failure.

void drm_gpuva_remove(struct drm_gpuva *va)¶: remove a drm_gpuva

Parameters

struct drm_gpuva *va: the drm_gpuva to remove

Description

This removes the given va from the underlaying tree.

It is safe to use this function using the safe versions of iterating the GPU VA space, such as drm_gpuva_for_each_va_safe() and drm_gpuva_for_each_va_range_safe().

void drm_gpuva_link(struct drm_gpuva *va)¶: link a drm_gpuva

Parameters

struct drm_gpuva *va: the drm_gpuva to link

Description

This adds the given va to the GPU VA list of the drm_gem_object it is associated with.

This function expects the caller to protect the GEM's GPUVA list against concurrent access using the GEMs dma_resv lock.

void drm_gpuva_unlink(struct drm_gpuva *va)¶: unlink a drm_gpuva

Parameters

struct drm_gpuva *va: the drm_gpuva to unlink

Description

This removes the given va from the GPU VA list of the drm_gem_object it is associated with.

This function expects the caller to protect the GEM's GPUVA list against concurrent access using the GEMs dma_resv lock.

struct drm_gpuva *drm_gpuva_find_first(struct drm_gpuva_manager *mgr, u64 addr, u64 range)¶: find the first drm_gpuva in the given range

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager to search in
u64 addr: the drm_gpuvas address
u64 range: the drm_gpuvas range

Return

the first drm_gpuva within the given range

struct drm_gpuva *drm_gpuva_find(struct drm_gpuva_manager *mgr, u64 addr, u64 range)¶: find a drm_gpuva

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager to search in
u64 addr: the drm_gpuvas address
u64 range: the drm_gpuvas range

Return

the drm_gpuva at a given addr and with a given range

struct drm_gpuva *drm_gpuva_find_prev(struct drm_gpuva_manager *mgr, u64 start)¶: find the drm_gpuva before the given address

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager to search in
u64 start: the given GPU VA's start address

Description

Find the adjacent drm_gpuva before the GPU VA with given start address.

Note that if there is any free space between the GPU VA mappings no mapping is returned.

Return

a pointer to the found drm_gpuva or NULL if none was found

struct drm_gpuva *drm_gpuva_find_next(struct drm_gpuva_manager *mgr, u64 end)¶: find the drm_gpuva after the given address

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager to search in
u64 end: the given GPU VA's end address

Description

Find the adjacent drm_gpuva after the GPU VA with given end address.

Note that if there is any free space between the GPU VA mappings no mapping is returned.

Return

a pointer to the found drm_gpuva or NULL if none was found

bool drm_gpuva_interval_empty(struct drm_gpuva_manager *mgr, u64 addr, u64 range)¶: indicate whether a given interval of the VA space is empty

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager to check the range for
u64 addr: the start address of the range
u64 range: the range of the interval

Return

true if the interval is empty, false otherwise

void drm_gpuva_map(struct drm_gpuva_manager *mgr, struct drm_gpuva *va, struct drm_gpuva_op_map *op)¶: helper to insert a drm_gpuva according to a drm_gpuva_op_map

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager
struct drm_gpuva *va: the drm_gpuva to insert
struct drm_gpuva_op_map *op: the drm_gpuva_op_map to initialize va with

Description

Initializes the va from the op and inserts it into the given mgr.

void drm_gpuva_remap(struct drm_gpuva *prev, struct drm_gpuva *next, struct drm_gpuva_op_remap *op)¶: helper to remap a drm_gpuva according to a drm_gpuva_op_remap

Parameters

struct drm_gpuva *prev: the drm_gpuva to remap when keeping the start of a mapping
struct drm_gpuva *next: the drm_gpuva to remap when keeping the end of a mapping
struct drm_gpuva_op_remap *op: the drm_gpuva_op_remap to initialize prev and next with

Description

Removes the currently mapped drm_gpuva and remaps it using prev and/or next.

void drm_gpuva_unmap(struct drm_gpuva_op_unmap *op)¶: helper to remove a drm_gpuva according to a drm_gpuva_op_unmap

Parameters

struct drm_gpuva_op_unmap *op: the drm_gpuva_op_unmap specifying the drm_gpuva to remove

Description

Removes the drm_gpuva associated with the drm_gpuva_op_unmap.

int drm_gpuva_sm_map(struct drm_gpuva_manager *mgr, void *priv, u64 req_addr, u64 req_range, struct drm_gem_object *req_obj, u64 req_offset)¶: creates the drm_gpuva_op split/merge steps

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager representing the GPU VA space
void *priv: pointer to a driver private data structure
u64 req_addr: the start address of the new mapping
u64 req_range: the range of the new mapping
struct drm_gem_object *req_obj: the drm_gem_object to map
u64 req_offset: the offset within the drm_gem_object

Description

This function iterates the given range of the GPU VA space. It utilizes the drm_gpuva_fn_ops to call back into the driver providing the split and merge steps.

Drivers may use these callbacks to update the GPU VA space right away within the callback. In case the driver decides to copy and store the operations for later processing neither this function nor drm_gpuva_sm_unmap is allowed to be called before the drm_gpuva_manager's view of the GPU VA space was updated with the previous set of operations. To update the drm_gpuva_manager's view of the GPU VA space drm_gpuva_insert(), drm_gpuva_destroy_locked() and/or drm_gpuva_destroy_unlocked() should be used.

A sequence of callbacks can contain map, unmap and remap operations, but the sequence of callbacks might also be empty if no operation is required, e.g. if the requested mapping already exists in the exact same way.

There can be an arbitrary amount of unmap operations, a maximum of two remap operations and a single map operation. The latter one represents the original map operation requested by the caller.

Return

0 on success or a negative error code

int drm_gpuva_sm_unmap(struct drm_gpuva_manager *mgr, void *priv, u64 req_addr, u64 req_range)¶: creates the drm_gpuva_ops to split on unmap

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager representing the GPU VA space
void *priv: pointer to a driver private data structure
u64 req_addr: the start address of the range to unmap
u64 req_range: the range of the mappings to unmap

Description

This function iterates the given range of the GPU VA space. It utilizes the drm_gpuva_fn_ops to call back into the driver providing the operations to unmap and, if required, split existent mappings.

Drivers may use these callbacks to update the GPU VA space right away within the callback. In case the driver decides to copy and store the operations for later processing neither this function nor drm_gpuva_sm_map is allowed to be called before the drm_gpuva_manager's view of the GPU VA space was updated with the previous set of operations. To update the drm_gpuva_manager's view of the GPU VA space drm_gpuva_insert(), drm_gpuva_destroy_locked() and/or drm_gpuva_destroy_unlocked() should be used.

A sequence of callbacks can contain unmap and remap operations, depending on whether there are actual overlapping mappings to split.

There can be an arbitrary amount of unmap operations and a maximum of two remap operations.

Return

0 on success or a negative error code

struct drm_gpuva_ops *drm_gpuva_sm_map_ops_create(struct drm_gpuva_manager *mgr, u64 req_addr, u64 req_range, struct drm_gem_object *req_obj, u64 req_offset)¶: creates the drm_gpuva_ops to split and merge

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager representing the GPU VA space
u64 req_addr: the start address of the new mapping
u64 req_range: the range of the new mapping
struct drm_gem_object *req_obj: the drm_gem_object to map
u64 req_offset: the offset within the drm_gem_object

Description

This function creates a list of operations to perform splitting and merging of existent mapping(s) with the newly requested one.

The list can be iterated with drm_gpuva_for_each_op and must be processed in the given order. It can contain map, unmap and remap operations, but it also can be empty if no operation is required, e.g. if the requested mapping already exists is the exact same way.

There can be an arbitrary amount of unmap operations, a maximum of two remap operations and a single map operation. The latter one represents the original map operation requested by the caller.

Note that before calling this function again with another mapping request it is necessary to update the drm_gpuva_manager's view of the GPU VA space. The previously obtained operations must be either processed or abandoned. To update the drm_gpuva_manager's view of the GPU VA space drm_gpuva_insert(), drm_gpuva_destroy_locked() and/or drm_gpuva_destroy_unlocked() should be used.

After the caller finished processing the returned drm_gpuva_ops, they must be freed with drm_gpuva_ops_free.

Return

a pointer to the drm_gpuva_ops on success, an ERR_PTR on failure

struct drm_gpuva_ops *drm_gpuva_sm_unmap_ops_create(struct drm_gpuva_manager *mgr, u64 req_addr, u64 req_range)¶: creates the drm_gpuva_ops to split on unmap

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager representing the GPU VA space
u64 req_addr: the start address of the range to unmap
u64 req_range: the range of the mappings to unmap

Description

This function creates a list of operations to perform unmapping and, if required, splitting of the mappings overlapping the unmap range.

The list can be iterated with drm_gpuva_for_each_op and must be processed in the given order. It can contain unmap and remap operations, depending on whether there are actual overlapping mappings to split.

There can be an arbitrary amount of unmap operations and a maximum of two remap operations.

Note that before calling this function again with another range to unmap it is necessary to update the drm_gpuva_manager's view of the GPU VA space. The previously obtained operations must be processed or abandoned. To update the drm_gpuva_manager's view of the GPU VA space drm_gpuva_insert(), drm_gpuva_destroy_locked() and/or drm_gpuva_destroy_unlocked() should be used.

After the caller finished processing the returned drm_gpuva_ops, they must be freed with drm_gpuva_ops_free.

Return

a pointer to the drm_gpuva_ops on success, an ERR_PTR on failure

struct drm_gpuva_ops *drm_gpuva_prefetch_ops_create(struct drm_gpuva_manager *mgr, u64 addr, u64 range)¶: creates the drm_gpuva_ops to prefetch

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager representing the GPU VA space
u64 addr: the start address of the range to prefetch
u64 range: the range of the mappings to prefetch

Description

This function creates a list of operations to perform prefetching.

The list can be iterated with drm_gpuva_for_each_op and must be processed in the given order. It can contain prefetch operations.

There can be an arbitrary amount of prefetch operations.

After the caller finished processing the returned drm_gpuva_ops, they must be freed with drm_gpuva_ops_free.

Return

a pointer to the drm_gpuva_ops on success, an ERR_PTR on failure

struct drm_gpuva_ops *drm_gpuva_gem_unmap_ops_create(struct drm_gpuva_manager *mgr, struct drm_gem_object *obj)¶: creates the drm_gpuva_ops to unmap a GEM

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager representing the GPU VA space
struct drm_gem_object *obj: the drm_gem_object to unmap

Description

This function creates a list of operations to perform unmapping for every GPUVA attached to a GEM.

The list can be iterated with drm_gpuva_for_each_op and consists out of an arbitrary amount of unmap operations.

After the caller finished processing the returned drm_gpuva_ops, they must be freed with drm_gpuva_ops_free.

It is the callers responsibility to protect the GEMs GPUVA list against concurrent access using the GEMs dma_resv lock.

Return

a pointer to the drm_gpuva_ops on success, an ERR_PTR on failure

void drm_gpuva_ops_free(struct drm_gpuva_manager *mgr, struct drm_gpuva_ops *ops)¶: free the given drm_gpuva_ops

Parameters

struct drm_gpuva_manager *mgr: the drm_gpuva_manager the ops were created for
struct drm_gpuva_ops *ops: the drm_gpuva_ops to free

Description

Frees the given drm_gpuva_ops structure including all the ops associated with it.

DRM Buddy Allocator¶

DRM Buddy Function References¶

int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)¶: init memory manager

Parameters

struct drm_buddy *mm: DRM buddy manager to initialize
u64 size: size in bytes to manage
u64 chunk_size: minimum page size in bytes for our allocations

Description

Initializes the memory manager and its resources.

Return

0 on success, error code on failure.

void drm_buddy_fini(struct drm_buddy *mm)¶: tear down the memory manager

Parameters

struct drm_buddy *mm: DRM buddy manager to free

Description

Cleanup memory manager resources and the freelist

struct drm_buddy_block *drm_get_buddy(struct drm_buddy_block *block)¶: get buddy address

Parameters

struct drm_buddy_block *block: DRM buddy block

Description

Returns the corresponding buddy block for block, or NULL if this is a root block and can't be merged further. Requires some kind of locking to protect against any concurrent allocate and free operations.

void drm_buddy_free_block(struct drm_buddy *mm, struct drm_buddy_block *block)¶: free a block

Parameters

struct drm_buddy *mm: DRM buddy manager
struct drm_buddy_block *block: block to be freed

void drm_buddy_free_list(struct drm_buddy *mm, struct list_head *objects)¶: free blocks

Parameters

struct drm_buddy *mm: DRM buddy manager
struct list_head *objects: input list head to free blocks

int drm_buddy_block_trim(struct drm_buddy *mm, u64 new_size, struct list_head *blocks)¶: free unused pages

Parameters

struct drm_buddy *mm: DRM buddy manager
u64 new_size: original size requested
struct list_head *blocks: Input and output list of allocated blocks. MUST contain single block as input to be trimmed. On success will contain the newly allocated blocks making up the new_size. Blocks always appear in ascending order

Description

For contiguous allocation, we round up the size to the nearest power of two value, drivers consume actual size, so remaining portions are unused and can be optionally freed with this function

Return

0 on success, error code on failure.

int drm_buddy_alloc_blocks(struct drm_buddy *mm, u64 start, u64 end, u64 size, u64 min_page_size, struct list_head *blocks, unsigned long flags)¶: allocate power-of-two blocks

Parameters

struct drm_buddy *mm: DRM buddy manager to allocate from
u64 start: start of the allowed range for this block
u64 end: end of the allowed range for this block
u64 size: size of the allocation
u64 min_page_size: alignment of the allocation
struct list_head *blocks: output list head to add allocated blocks
unsigned long flags: DRM_BUDDY_*_ALLOCATION flags

Description

alloc_range_bias() called on range limitations, which traverses the tree and returns the desired block.

alloc_from_freelist() called when no range restrictions are enforced, which picks the block from the freelist.

Return

0 on success, error code on failure.

void drm_buddy_block_print(struct drm_buddy *mm, struct drm_buddy_block *block, struct drm_printer *p)¶: print block information

Parameters

struct drm_buddy *mm: DRM buddy manager
struct drm_buddy_block *block: DRM buddy block
struct drm_printer *p: DRM printer to use

void drm_buddy_print(struct drm_buddy *mm, struct drm_printer *p)¶: print allocator state

Parameters

struct drm_buddy *mm: DRM buddy manager
struct drm_printer *p: DRM printer to use

DRM Cache Handling and Fast WC memcpy()¶

void drm_clflush_pages(struct page *pages[], unsigned long num_pages)¶: Flush dcache lines of a set of pages.

Parameters

struct page *pages[]: List of pages to be flushed.
unsigned long num_pages: Number of pages in the array.

Description

Flush every data cache line entry that points to an address belonging to a page in the array.

void drm_clflush_sg(struct sg_table *st)¶: Flush dcache lines pointing to a scather-gather.

Parameters

struct sg_table *st: struct sg_table.

Description

Flush every data cache line entry that points to an address in the sg.

void drm_clflush_virt_range(void *addr, unsigned long length)¶: Flush dcache lines of a region

Parameters

void *addr: Initial kernel memory address.
unsigned long length: Region size.

Description

Flush every data cache line entry that points to an address in the region requested.

void drm_memcpy_from_wc(struct iosys_map *dst, const struct iosys_map *src, unsigned long len)¶: Perform the fastest available memcpy from a source that may be WC.

Parameters

struct iosys_map *dst: The destination pointer
const struct iosys_map *src: The source pointer
unsigned long len: The size of the area o transfer in bytes

Description

Tries an arch optimized memcpy for prefetching reading out of a WC region, and if no such beast is available, falls back to a normal memcpy.

DRM Sync Objects¶

DRM synchronisation objects (syncobj, see struct drm_syncobj) provide a container for a synchronization primitive which can be used by userspace to explicitly synchronize GPU commands, can be shared between userspace processes, and can be shared between different DRM drivers. Their primary use-case is to implement Vulkan fences and semaphores. The syncobj userspace API provides ioctls for several operations:

Creation and destruction of syncobjs

Import and export of syncobjs to/from a syncobj file descriptor

Import and export a syncobj's underlying fence to/from a sync file

Reset a syncobj (set its fence to NULL)

Signal a syncobj (set a trivially signaled fence)

Wait for a syncobj's fence to appear and be signaled

The syncobj userspace API also provides operations to manipulate a syncobj in terms of a timeline of struct dma_fence_chain rather than a single struct dma_fence, through the following operations:

Signal a given point on the timeline

Wait for a given point to appear and/or be signaled

Import and export from/to a given point of a timeline

At it's core, a syncobj is simply a wrapper around a pointer to a struct dma_fence which may be NULL. When a syncobj is first created, its pointer is either NULL or a pointer to an already signaled fence depending on whether the DRM_SYNCOBJ_CREATE_SIGNALED flag is passed to DRM_IOCTL_SYNCOBJ_CREATE.

If the syncobj is considered as a binary (its state is either signaled or unsignaled) primitive, when GPU work is enqueued in a DRM driver to signal the syncobj, the syncobj's fence is replaced with a fence which will be signaled by the completion of that work. If the syncobj is considered as a timeline primitive, when GPU work is enqueued in a DRM driver to signal the a given point of the syncobj, a new struct dma_fence_chain pointing to the DRM driver's fence and also pointing to the previous fence that was in the syncobj. The new struct dma_fence_chain fence replace the syncobj's fence and will be signaled by completion of the DRM driver's work and also any work associated with the fence previously in the syncobj.

When GPU work which waits on a syncobj is enqueued in a DRM driver, at the time the work is enqueued, it waits on the syncobj's fence before submitting the work to hardware. That fence is either :

The syncobj's current fence if the syncobj is considered as a binary primitive.

The struct dma_fence associated with a given point if the syncobj is considered as a timeline primitive.

If the syncobj's fence is NULL or not present in the syncobj's timeline, the enqueue operation is expected to fail.

With binary syncobj, all manipulation of the syncobjs's fence happens in terms of the current fence at the time the ioctl is called by userspace regardless of whether that operation is an immediate host-side operation (signal or reset) or or an operation which is enqueued in some driver queue. DRM_IOCTL_SYNCOBJ_RESET and DRM_IOCTL_SYNCOBJ_SIGNAL can be used to manipulate a syncobj from the host by resetting its pointer to NULL or setting its pointer to a fence which is already signaled.

With a timeline syncobj, all manipulation of the synobj's fence happens in terms of a u64 value referring to point in the timeline. See dma_fence_chain_find_seqno() to see how a given point is found in the timeline.

Note that applications should be careful to always use timeline set of ioctl() when dealing with syncobj considered as timeline. Using a binary set of ioctl() with a syncobj considered as timeline could result incorrect synchronization. The use of binary syncobj is supported through the timeline set of ioctl() by using a point value of 0, this will reproduce the behavior of the binary set of ioctl() (for example replace the syncobj's fence when signaling).

Host-side wait on syncobjs¶

DRM_IOCTL_SYNCOBJ_WAIT takes an array of syncobj handles and does a host-side wait on all of the syncobj fences simultaneously. If DRM_SYNCOBJ_WAIT_FLAGS_WAIT_ALL is set, the wait ioctl will wait on all of the syncobj fences to be signaled before it returns. Otherwise, it returns once at least one syncobj fence has been signaled and the index of a signaled fence is written back to the client.

Unlike the enqueued GPU work dependencies which fail if they see a NULL fence in a syncobj, if DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT is set, the host-side wait will first wait for the syncobj to receive a non-NULL fence and then wait on that fence. If DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT is not set and any one of the syncobjs in the array has a NULL fence, -EINVAL will be returned. Assuming the syncobj starts off with a NULL fence, this allows a client to do a host wait in one thread (or process) which waits on GPU work submitted in another thread (or process) without having to manually synchronize between the two. This requirement is inherited from the Vulkan fence API.

Similarly, DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT takes an array of syncobj handles as well as an array of u64 points and does a host-side wait on all of syncobj fences at the given points simultaneously.

DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT also adds the ability to wait for a given fence to materialize on the timeline without waiting for the fence to be signaled by using the DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE flag. This requirement is inherited from the wait-before-signal behavior required by the Vulkan timeline semaphore API.

Alternatively, DRM_IOCTL_SYNCOBJ_EVENTFD can be used to wait without blocking: an eventfd will be signaled when the syncobj is. This is useful to integrate the wait in an event loop.

Import/export of syncobjs¶

DRM_IOCTL_SYNCOBJ_FD_TO_HANDLE and DRM_IOCTL_SYNCOBJ_HANDLE_TO_FD provide two mechanisms for import/export of syncobjs.

The first lets the client import or export an entire syncobj to a file descriptor. These fd's are opaque and have no other use case, except passing the syncobj between processes. All exported file descriptors and any syncobj handles created as a result of importing those file descriptors own a reference to the same underlying struct drm_syncobj and the syncobj can be used persistently across all the processes with which it is shared. The syncobj is freed only once the last reference is dropped. Unlike dma-buf, importing a syncobj creates a new handle (with its own reference) for every import instead of de-duplicating. The primary use-case of this persistent import/export is for shared Vulkan fences and semaphores.

The second import/export mechanism, which is indicated by DRM_SYNCOBJ_FD_TO_HANDLE_FLAGS_IMPORT_SYNC_FILE or DRM_SYNCOBJ_HANDLE_TO_FD_FLAGS_EXPORT_SYNC_FILE lets the client import/export the syncobj's current fence from/to a sync_file. When a syncobj is exported to a sync file, that sync file wraps the sycnobj's fence at the time of export and any later signal or reset operations on the syncobj will not affect the exported sync file. When a sync file is imported into a syncobj, the syncobj's fence is set to the fence wrapped by that sync file. Because sync files are immutable, resetting or signaling the syncobj will not affect any sync files whose fences have been imported into the syncobj.

Import/export of timeline points in timeline syncobjs¶

DRM_IOCTL_SYNCOBJ_TRANSFER provides a mechanism to transfer a struct dma_fence_chain of a syncobj at a given u64 point to another u64 point into another syncobj.

Note that if you want to transfer a struct dma_fence_chain from a given point on a timeline syncobj from/into a binary syncobj, you can use the point 0 to mean take/replace the fence in the syncobj.

struct drm_syncobj¶: sync object.

Definition:

struct drm_syncobj {
    struct kref refcount;
    struct dma_fence __rcu *fence;
    struct list_head cb_list;
    struct list_head ev_fd_list;
    spinlock_t lock;
    struct file *file;
};

Members

refcount

Reference count of this object.

fence

NULL or a pointer to the fence bound to this object.

This field should not be used directly. Use drm_syncobj_fence_get() and drm_syncobj_replace_fence() instead.

cb_list

List of callbacks to call when the fence gets replaced.

ev_fd_list

List of registered eventfd.

lock

Protects cb_list and ev_fd_list, and write-locks fence.

file

A file backing for this syncobj.

Description

This structure defines a generic sync object which wraps a dma_fence.

void drm_syncobj_get(struct drm_syncobj *obj)¶: acquire a syncobj reference

Parameters

struct drm_syncobj *obj: sync object

Description

This acquires an additional reference to obj. It is illegal to call this without already holding a reference. No locks required.

void drm_syncobj_put(struct drm_syncobj *obj)¶: release a reference to a sync object.

Parameters

struct drm_syncobj *obj: sync object.

struct dma_fence *drm_syncobj_fence_get(struct drm_syncobj *syncobj)¶: get a reference to a fence in a sync object

Parameters

struct drm_syncobj *syncobj: sync object.

Description

This acquires additional reference to drm_syncobj.fence contained in obj, if not NULL. It is illegal to call this without already holding a reference. No locks required.

Return

Either the fence of obj or NULL if there's none.

struct drm_syncobj *drm_syncobj_find(struct drm_file *file_private, u32 handle)¶: lookup and reference a sync object.

Parameters

struct drm_file *file_private: drm file private pointer
u32 handle: sync object handle to lookup.

Description

Returns a reference to the syncobj pointed to by handle or NULL. The reference must be released by calling drm_syncobj_put().

void drm_syncobj_add_point(struct drm_syncobj *syncobj, struct dma_fence_chain *chain, struct dma_fence *fence, uint64_t point)¶: add new timeline point to the syncobj

Parameters

struct drm_syncobj *syncobj: sync object to add timeline point do
struct dma_fence_chain *chain: chain node to use to add the point
struct dma_fence *fence: fence to encapsulate in the chain node
uint64_t point: sequence number to use for the point

Description

Add the chain node as new timeline point to the syncobj.

void drm_syncobj_replace_fence(struct drm_syncobj *syncobj, struct dma_fence *fence)¶: replace fence in a sync object.

Parameters

struct drm_syncobj *syncobj: Sync object to replace fence in
struct dma_fence *fence: fence to install in sync file.

Description

This replaces the fence on a sync object.

int drm_syncobj_find_fence(struct drm_file *file_private, u32 handle, u64 point, u64 flags, struct dma_fence **fence)¶: lookup and reference the fence in a sync object

Parameters

struct drm_file *file_private: drm file private pointer
u32 handle: sync object handle to lookup.
u64 point: timeline point
u64 flags: DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT or not
struct dma_fence **fence: out parameter for the fence

Description

This is just a convenience function that combines drm_syncobj_find() and drm_syncobj_fence_get().

Returns 0 on success or a negative error value on failure. On success fence contains a reference to the fence, which must be released by calling dma_fence_put().

void drm_syncobj_free(struct kref *kref)¶: free a sync object.

Parameters

struct kref *kref: kref to free.

Description

Only to be called from kref_put in drm_syncobj_put.

int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags, struct dma_fence *fence)¶: create a new syncobj

Parameters

struct drm_syncobj **out_syncobj: returned syncobj
uint32_t flags: DRM_SYNCOBJ_* flags
struct dma_fence *fence: if non-NULL, the syncobj will represent this fence

Description

This is the first function to create a sync object. After creating, drivers probably want to make it available to userspace, either through drm_syncobj_get_handle() or drm_syncobj_get_fd().

Returns 0 on success or a negative error value on failure.

int drm_syncobj_get_handle(struct drm_file *file_private, struct drm_syncobj *syncobj, u32 *handle)¶: get a handle from a syncobj

Parameters

struct drm_file *file_private: drm file private pointer
struct drm_syncobj *syncobj: Sync object to export
u32 *handle: out parameter with the new handle

Description

Exports a sync object created with drm_syncobj_create() as a handle on file_private to userspace.

Returns 0 on success or a negative error value on failure.

int drm_syncobj_get_fd(struct drm_syncobj *syncobj, int *p_fd)¶: get a file descriptor from a syncobj

Parameters

struct drm_syncobj *syncobj: Sync object to export
int *p_fd: out parameter with the new file descriptor

Description

Exports a sync object created with drm_syncobj_create() as a file descriptor.

Returns 0 on success or a negative error value on failure.

signed long drm_timeout_abs_to_jiffies(int64_t timeout_nsec)¶: calculate jiffies timeout from absolute value

Parameters

int64_t timeout_nsec: timeout nsec component in ns, 0 for poll

Description

Calculate the timeout in jiffies from an absolute time in sec/nsec.

DRM Execution context¶

This component mainly abstracts the retry loop necessary for locking multiple GEM objects while preparing hardware operations (e.g. command submissions, page table updates etc..).

If a contention is detected while locking a GEM object the cleanup procedure unlocks all previously locked GEM objects and locks the contended one first before locking any further objects.

After an object is locked fences slots can optionally be reserved on the dma_resv object inside the GEM object.

A typical usage pattern should look like this:

struct drm_gem_object *obj;
struct drm_exec exec;
unsigned long index;
int ret;

drm_exec_init(&exec, DRM_EXEC_INTERRUPTIBLE_WAIT);
drm_exec_until_all_locked(&exec) {
        ret = drm_exec_prepare_obj(&exec, boA, 1);
        drm_exec_retry_on_contention(&exec);
        if (ret)
                goto error;

        ret = drm_exec_prepare_obj(&exec, boB, 1);
        drm_exec_retry_on_contention(&exec);
        if (ret)
                goto error;
}

drm_exec_for_each_locked_object(&exec, index, obj) {
        dma_resv_add_fence(obj->resv, fence, DMA_RESV_USAGE_READ);
        ...
}
drm_exec_fini(&exec);

See struct dma_exec for more details.

struct drm_exec¶: Execution context

Definition:

struct drm_exec {
    uint32_t flags;
    struct ww_acquire_ctx   ticket;
    unsigned int            num_objects;
    unsigned int            max_objects;
    struct drm_gem_object   **objects;
    struct drm_gem_object   *contended;
    struct drm_gem_object *prelocked;
};

Members

flags: Flags to control locking behavior
ticket: WW ticket used for acquiring locks
num_objects: number of objects locked
max_objects: maximum objects in array
objects: array of the locked objects
contended: contended GEM object we backed off for
prelocked: already locked GEM object due to contention

struct drm_gem_object *drm_exec_obj(struct drm_exec *exec, unsigned long index)¶: Return the object for a give drm_exec index

Parameters

struct drm_exec *exec: Pointer to the drm_exec context
unsigned long index: The index.

Return

Pointer to the locked object corresponding to index if index is within the number of locked objects. NULL otherwise.

drm_exec_for_each_locked_object¶

drm_exec_for_each_locked_object (exec, index, obj)

iterate over all the locked objects

Parameters

exec: drm_exec object
index: unsigned long index for the iteration
obj: the current GEM object

Description

Iterate over all the locked GEM objects inside the drm_exec object.

drm_exec_for_each_locked_object_reverse¶

drm_exec_for_each_locked_object_reverse (exec, index, obj)

iterate over all the locked objects in reverse locking order

Parameters

exec: drm_exec object
index: unsigned long index for the iteration
obj: the current GEM object

Description

Iterate over all the locked GEM objects inside the drm_exec object in reverse locking order. Note that index may go below zero and wrap, but that will be caught by drm_exec_obj(), returning a NULL object.

drm_exec_until_all_locked¶

drm_exec_until_all_locked (exec)

loop until all GEM objects are locked

Parameters

exec: drm_exec object

Description

Core functionality of the drm_exec object. Loops until all GEM objects are locked and no more contention exists. At the beginning of the loop it is guaranteed that no GEM object is locked.

Since labels can't be defined local to the loops body we use a jump pointer to make sure that the retry is only used from within the loops body.

drm_exec_retry_on_contention¶

drm_exec_retry_on_contention (exec)

restart the loop to grap all locks

Parameters

exec: drm_exec object

Description

Control flow helper to continue when a contention was detected and we need to clean up and re-start the loop to prepare all GEM objects.

bool drm_exec_is_contended(struct drm_exec *exec)¶: check for contention

Parameters

struct drm_exec *exec: drm_exec object

Description

Returns true if the drm_exec object has run into some contention while locking a GEM object and needs to clean up.

void drm_exec_init(struct drm_exec *exec, uint32_t flags)¶: initialize a drm_exec object

Parameters

struct drm_exec *exec: the drm_exec object to initialize
uint32_t flags: controls locking behavior, see DRM_EXEC_* defines

Description

Initialize the object and make sure that we can track locked objects.

void drm_exec_fini(struct drm_exec *exec)¶: finalize a drm_exec object

Parameters

struct drm_exec *exec: the drm_exec object to finalize

Description

Unlock all locked objects, drop the references to objects and free all memory used for tracking the state.

bool drm_exec_cleanup(struct drm_exec *exec)¶: cleanup when contention is detected

Parameters

struct drm_exec *exec: the drm_exec object to cleanup

Description

Cleanup the current state and return true if we should stay inside the retry loop, false if there wasn't any contention detected and we can keep the objects locked.

int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object *obj)¶: lock a GEM object for use

Parameters

struct drm_exec *exec: the drm_exec object with the state
struct drm_gem_object *obj: the GEM object to lock

Description

Lock a GEM object for use and grab a reference to it.

Return

-EDEADLK if a contention is detected, -EALREADY when object is already locked (can be suppressed by setting the DRM_EXEC_IGNORE_DUPLICATES flag), -ENOMEM when memory allocation failed and zero for success.

void drm_exec_unlock_obj(struct drm_exec *exec, struct drm_gem_object *obj)¶: unlock a GEM object in this exec context

Parameters

struct drm_exec *exec: the drm_exec object with the state
struct drm_gem_object *obj: the GEM object to unlock

Description

Unlock the GEM object and remove it from the collection of locked objects. Should only be used to unlock the most recently locked objects. It's not time efficient to unlock objects locked long ago.

int drm_exec_prepare_obj(struct drm_exec *exec, struct drm_gem_object *obj, unsigned int num_fences)¶: prepare a GEM object for use

Parameters

struct drm_exec *exec: the drm_exec object with the state
struct drm_gem_object *obj: the GEM object to prepare
unsigned int num_fences: how many fences to reserve

Description

Prepare a GEM object for use by locking it and reserving fence slots.

Return

-EDEADLK if a contention is detected, -EALREADY when object is already locked, -ENOMEM when memory allocation failed and zero for success.

int drm_exec_prepare_array(struct drm_exec *exec, struct drm_gem_object **objects, unsigned int num_objects, unsigned int num_fences)¶: helper to prepare an array of objects

Parameters

struct drm_exec *exec: the drm_exec object with the state
struct drm_gem_object **objects: array of GEM object to prepare
unsigned int num_objects: number of GEM objects in the array
unsigned int num_fences: number of fences to reserve on each GEM object

Description

Prepares all GEM objects in an array, aborts on first error. Reserves num_fences on each GEM object after locking it.

Return

-EDEADLOCK on contention, -EALREADY when object is already locked, -ENOMEM when memory allocation failed and zero for success.

GPU Scheduler¶

Overview¶

The GPU scheduler provides entities which allow userspace to push jobs into software queues which are then scheduled on a hardware run queue. The software queues have a priority among them. The scheduler selects the entities from the run queue using a FIFO. The scheduler provides dependency handling features among jobs. The driver is supposed to provide callback functions for backend operations to the scheduler like submitting a job to hardware run queue, returning the dependencies of a job etc.

The organisation of the scheduler is the following:

Each hw run queue has one scheduler
Each scheduler has multiple run queues with different priorities (e.g., HIGH_HW,HIGH_SW, KERNEL, NORMAL)
Each scheduler run queue has a queue of entities to schedule
Entities themselves maintain a queue of jobs that will be scheduled on the hardware.

The jobs in a entity are always scheduled in the order that they were pushed.

Note that once a job was taken from the entities queue and pushed to the hardware, i.e. the pending queue, the entity must not be referenced anymore through the jobs entity pointer.

Scheduler Function References¶

DRM_SCHED_FENCE_DONT_PIPELINE¶

DRM_SCHED_FENCE_DONT_PIPELINE ()

Prefent dependency pipelining

Parameters

Description

Setting this flag on a scheduler fence prevents pipelining of jobs depending on this fence. In other words we always insert a full CPU round trip before dependen jobs are pushed to the hw queue.

DRM_SCHED_FENCE_FLAG_HAS_DEADLINE_BIT¶

DRM_SCHED_FENCE_FLAG_HAS_DEADLINE_BIT ()

A fence deadline hint has been set

Parameters

Description

Because we could have a deadline hint can be set before the backing hw fence is created, we need to keep track of whether a deadline has already been set.

struct drm_sched_entity¶: A wrapper around a job queue (typically attached to the DRM file_priv).

Definition:

struct drm_sched_entity {
    struct list_head                list;
    struct drm_sched_rq             *rq;
    struct drm_gpu_scheduler        **sched_list;
    unsigned int                    num_sched_list;
    enum drm_sched_priority         priority;
    spinlock_t rq_lock;
    struct spsc_queue               job_queue;
    atomic_t fence_seq;
    uint64_t fence_context;
    struct dma_fence                *dependency;
    struct dma_fence_cb             cb;
    atomic_t *guilty;
    struct dma_fence __rcu          *last_scheduled;
    struct task_struct              *last_user;
    bool stopped;
    struct completion               entity_idle;
    ktime_t oldest_job_waiting;
    struct rb_node                  rb_tree_node;
};

Members

list

Used to append this struct to the list of entities in the runqueue rq under drm_sched_rq.entities.

Protected by drm_sched_rq.lock of rq.

rq

Runqueue on which this entity is currently scheduled.

FIXME: Locking is very unclear for this. Writers are protected by rq_lock, but readers are generally lockless and seem to just race with not even a READ_ONCE.

sched_list

A list of schedulers (struct drm_gpu_scheduler). Jobs from this entity can be scheduled on any scheduler on this list.

This can be modified by calling drm_sched_entity_modify_sched(). Locking is entirely up to the driver, see the above function for more details.

This will be set to NULL if num_sched_list equals 1 and rq has been set already.

FIXME: This means priority changes through drm_sched_entity_set_priority() will be lost henceforth in this case.

num_sched_list

Number of drm_gpu_schedulers in the sched_list.

priority

Priority of the entity. This can be modified by calling drm_sched_entity_set_priority(). Protected by rq_lock.

rq_lock

Lock to modify the runqueue to which this entity belongs.

job_queue

the list of jobs of this entity.

fence_seq

A linearly increasing seqno incremented with each new drm_sched_fence which is part of the entity.

FIXME: Callers of drm_sched_job_arm() need to ensure correct locking, this doesn't need to be atomic.

fence_context

A unique context for all the fences which belong to this entity. The drm_sched_fence.scheduled uses the fence_context but drm_sched_fence.finished uses fence_context + 1.

dependency

The dependency fence of the job which is on the top of the job queue.

cb

Callback for the dependency fence above.

guilty

Points to entities' guilty.

last_scheduled

Points to the finished fence of the last scheduled job. Only written by the scheduler thread, can be accessed locklessly from drm_sched_job_arm() iff the queue is empty.

last_user

last group leader pushing a job into the entity.

stopped

Marks the enity as removed from rq and destined for termination. This is set by calling drm_sched_entity_flush() and by drm_sched_fini().

entity_idle

Signals when entity is not in use, used to sequence entity cleanup in drm_sched_entity_fini().

oldest_job_waiting

Marks earliest job waiting in SW queue

rb_tree_node

The node used to insert this entity into time based priority queue

Description

Entities will emit jobs in order to their corresponding hardware ring, and the scheduler will alternate between entities based on scheduling policy.

struct drm_sched_rq¶: queue of entities to be scheduled.

Definition:

struct drm_sched_rq {
    spinlock_t lock;
    struct drm_gpu_scheduler        *sched;
    struct list_head                entities;
    struct drm_sched_entity         *current_entity;
    struct rb_root_cached           rb_tree_root;
};

Members

lock: to modify the entities list.
sched: the scheduler to which this rq belongs to.
entities: list of the entities to be scheduled.
current_entity: the entity which is to be scheduled.
rb_tree_root: root of time based priory queue of entities for FIFO scheduling

Description

Run queue is a set of entities scheduling command submissions for one specific ring. It implements the scheduling policy that selects the next entity to emit commands from.

struct drm_sched_fence¶: fences corresponding to the scheduling of a job.

Definition:

struct drm_sched_fence {
    struct dma_fence                scheduled;
    struct dma_fence                finished;
    ktime_t deadline;
    struct dma_fence                *parent;
    struct drm_gpu_scheduler        *sched;
    spinlock_t lock;
    void *owner;
};

Members

scheduled

this fence is what will be signaled by the scheduler when the job is scheduled.

finished

this fence is what will be signaled by the scheduler when the job is completed.

When setting up an out fence for the job, you should use this, since it's available immediately upon drm_sched_job_init(), and the fence returned by the driver from run_job() won't be created until the dependencies have resolved.

deadline

deadline set on drm_sched_fence.finished which potentially needs to be propagated to drm_sched_fence.parent

parent

the fence returned by drm_sched_backend_ops.run_job when scheduling the job on hardware. We signal the drm_sched_fence.finished fence once parent is signalled.

sched

the scheduler instance to which the job having this struct belongs to.

lock

the lock used by the scheduled and the finished fences.

owner

job owner for debugging

struct drm_sched_job¶: A job to be run by an entity.

Definition:

struct drm_sched_job {
    struct spsc_node                queue_node;
    struct list_head                list;
    struct drm_gpu_scheduler        *sched;
    struct drm_sched_fence          *s_fence;
    union {
        struct dma_fence_cb             finish_cb;
        struct work_struct              work;
    };
    uint64_t id;
    atomic_t karma;
    enum drm_sched_priority         s_priority;
    struct drm_sched_entity         *entity;
    struct dma_fence_cb             cb;
    struct xarray                   dependencies;
    unsigned long                   last_dependency;
    ktime_t submit_ts;
};

Members

queue_node: used to append this struct to the queue of jobs in an entity.
list: a job participates in a "pending" and "done" lists.
sched: the scheduler instance on which this job is scheduled.
s_fence: contains the fences for the scheduling of job.
{unnamed_union}: anonymous
finish_cb: the callback for the finished fence.
work: Helper to reschdeule job kill to different context.
id: a unique id assigned to each job scheduled on the scheduler.
karma: increment on every hang caused by this job. If this exceeds the hang limit of the scheduler then the job is marked guilty and will not be scheduled further.
s_priority: the priority of the job.
entity: the entity to which this job belongs.
cb: the callback for the parent fence in s_fence.
dependencies: Contains the dependencies as struct dma_fence for this job, see drm_sched_job_add_dependency() and drm_sched_job_add_implicit_dependencies().
last_dependency: tracks dependencies as they signal
submit_ts: When the job was pushed into the entity queue.

Description

A job is created by the driver using drm_sched_job_init(), and should call drm_sched_entity_push_job() once it wants the scheduler to schedule the job.

struct drm_sched_backend_ops¶: Define the backend operations called by the scheduler

Definition:

struct drm_sched_backend_ops {
    struct dma_fence *(*prepare_job)(struct drm_sched_job *sched_job, struct drm_sched_entity *s_entity);
    struct dma_fence *(*run_job)(struct drm_sched_job *sched_job);
    enum drm_gpu_sched_stat (*timedout_job)(struct drm_sched_job *sched_job);
    void (*free_job)(struct drm_sched_job *sched_job);
};

Members

prepare_job

Called when the scheduler is considering scheduling this job next, to get another struct dma_fence for this job to block on. Once it returns NULL, run_job() may be called.

Can be NULL if no additional preparation to the dependencies are necessary. Skipped when jobs are killed instead of run.

run_job

Called to execute the job once all of the dependencies have been resolved. This may be called multiple times, if timedout_job() has happened and drm_sched_job_recovery() decides to try it again.

timedout_job

Called when a job has taken too long to execute, to trigger GPU recovery.

This method is called in a workqueue context.

Drivers typically issue a reset to recover from GPU hangs, and this procedure usually follows the following workflow:

Stop the scheduler using drm_sched_stop(). This will park the scheduler thread and cancel the timeout work, guaranteeing that nothing is queued while we reset the hardware queue
Try to gracefully stop non-faulty jobs (optional)
Issue a GPU reset (driver-specific)
Re-submit jobs using drm_sched_resubmit_jobs()
Restart the scheduler using drm_sched_start(). At that point, new jobs can be queued, and the scheduler thread is unblocked

Note that some GPUs have distinct hardware queues but need to reset the GPU globally, which requires extra synchronization between the timeout handler of the different drm_gpu_scheduler. One way to achieve this synchronization is to create an ordered workqueue (using alloc_ordered_workqueue()) at the driver level, and pass this queue to drm_sched_init(), to guarantee that timeout handlers are executed sequentially. The above workflow needs to be slightly adjusted in that case:

Stop all schedulers impacted by the reset using drm_sched_stop()
Try to gracefully stop non-faulty jobs on all queues impacted by the reset (optional)
Issue a GPU reset on all faulty queues (driver-specific)
Re-submit jobs on all schedulers impacted by the reset using drm_sched_resubmit_jobs()
Restart all schedulers that were stopped in step #1 using drm_sched_start()

Return DRM_GPU_SCHED_STAT_NOMINAL, when all is normal, and the underlying driver has started or completed recovery.

Return DRM_GPU_SCHED_STAT_ENODEV, if the device is no longer available, i.e. has been unplugged.

free_job

Called once the job's finished fence has been signaled and it's time to clean it up.

Description

These functions should be implemented in the driver side.

struct drm_gpu_scheduler¶: scheduler instance-specific data

Definition:

struct drm_gpu_scheduler {
    const struct drm_sched_backend_ops      *ops;
    uint32_t hw_submission_limit;
    long timeout;
    const char                      *name;
    struct drm_sched_rq             sched_rq[DRM_SCHED_PRIORITY_COUNT];
    wait_queue_head_t wake_up_worker;
    wait_queue_head_t job_scheduled;
    atomic_t hw_rq_count;
    atomic64_t job_id_count;
    struct workqueue_struct         *timeout_wq;
    struct delayed_work             work_tdr;
    struct task_struct              *thread;
    struct list_head                pending_list;
    spinlock_t job_list_lock;
    int hang_limit;
    atomic_t *score;
    atomic_t _score;
    bool ready;
    bool free_guilty;
    struct device                   *dev;
};

Members

ops: backend operations provided by the driver.
hw_submission_limit: the max size of the hardware queue.
timeout: the time after which a job is removed from the scheduler.
name: name of the ring for which this scheduler is being used.
sched_rq: priority wise array of run queues.
wake_up_worker: the wait queue on which the scheduler sleeps until a job is ready to be scheduled.
job_scheduled: once drm_sched_entity_do_release is called the scheduler waits on this wait queue until all the scheduled jobs are finished.
hw_rq_count: the number of jobs currently in the hardware queue.
job_id_count: used to assign unique id to the each job.
timeout_wq: workqueue used to queue work_tdr
work_tdr: schedules a delayed call to drm_sched_job_timedout after the timeout interval is over.
thread: the kthread on which the scheduler which run.
pending_list: the list of jobs which are currently in the job queue.
job_list_lock: lock to protect the pending_list.
hang_limit: once the hangs by a job crosses this limit then it is marked guilty and it will no longer be considered for scheduling.
score: score to help loadbalancer pick a idle sched
_score: score used when the driver doesn't provide one
ready: marks if the underlying HW is ready to work
free_guilty: A hit to time out handler to free the guilty job.
dev: system struct device

Description

One scheduler is implemented for each hardware ring.

void drm_sched_fault(struct drm_gpu_scheduler *sched)¶: immediately start timeout handler

Parameters

struct drm_gpu_scheduler *sched: scheduler where the timeout handling should be started.

Description

Start timeout handling immediately when the driver detects a hardware fault.

unsigned long drm_sched_suspend_timeout(struct drm_gpu_scheduler *sched)¶: Suspend scheduler job timeout

Parameters

struct drm_gpu_scheduler *sched: scheduler instance for which to suspend the timeout

Description

Suspend the delayed work timeout for the scheduler. This is done by modifying the delayed work timeout to an arbitrary large value, MAX_SCHEDULE_TIMEOUT in this case.

Returns the timeout remaining

void drm_sched_resume_timeout(struct drm_gpu_scheduler *sched, unsigned long remaining)¶: Resume scheduler job timeout

Parameters

struct drm_gpu_scheduler *sched: scheduler instance for which to resume the timeout
unsigned long remaining: remaining timeout

Description

Resume the delayed work timeout for the scheduler.

void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)¶: stop the scheduler

Parameters

struct drm_gpu_scheduler *sched: scheduler instance
struct drm_sched_job *bad: job which caused the time out

Description

Stop the scheduler and also removes and frees all completed jobs.

Note

bad job will not be freed as it might be used later and so it's callers responsibility to release it manually if it's not part of the pending list any more.

void drm_sched_start(struct drm_gpu_scheduler *sched, bool full_recovery)¶: recover jobs after a reset

Parameters

struct drm_gpu_scheduler *sched: scheduler instance
bool full_recovery: proceed with complete sched restart

void drm_sched_resubmit_jobs(struct drm_gpu_scheduler *sched)¶: Deprecated, don't use in new code!

Parameters

struct drm_gpu_scheduler *sched: scheduler instance

Description

Re-submitting jobs was a concept AMD came up as cheap way to implement recovery after a job timeout.

This turned out to be not working very well. First of all there are many problem with the dma_fence implementation and requirements. Either the implementation is risking deadlocks with core memory management or violating documented implementation details of the dma_fence object.

Drivers can still save and restore their state for recovery operations, but we shouldn't make this a general scheduler feature around the dma_fence interface.

int drm_sched_job_init(struct drm_sched_job *job, struct drm_sched_entity *entity, void *owner)¶: init a scheduler job

Parameters

struct drm_sched_job *job: scheduler job to init
struct drm_sched_entity *entity: scheduler entity to use
void *owner: job owner for debugging

Description

Refer to drm_sched_entity_push_job() documentation for locking considerations.

Drivers must make sure drm_sched_job_cleanup() if this function returns successfully, even when job is aborted before drm_sched_job_arm() is called.

WARNING: amdgpu abuses drm_sched.ready to signal when the hardware has died, which can mean that there's no valid runqueue for a entity. This function returns -ENOENT in this case (which probably should be -EIO as a more meanigful return value).

Returns 0 for success, negative error code otherwise.

void drm_sched_job_arm(struct drm_sched_job *job)¶: arm a scheduler job for execution

Parameters

struct drm_sched_job *job: scheduler job to arm

Description

This arms a scheduler job for execution. Specifically it initializes the drm_sched_job.s_fence of job, so that it can be attached to struct dma_resv or other places that need to track the completion of this job.

Refer to drm_sched_entity_push_job() documentation for locking considerations.

This can only be called if drm_sched_job_init() succeeded.

int drm_sched_job_add_dependency(struct drm_sched_job *job, struct dma_fence *fence)¶: adds the fence as a job dependency

Parameters

struct drm_sched_job *job: scheduler job to add the dependencies to
struct dma_fence *fence: the dma_fence to add to the list of dependencies.

Description

Note that fence is consumed in both the success and error cases.

Return

0 on success, or an error on failing to expand the array.

int drm_sched_job_add_syncobj_dependency(struct drm_sched_job *job, struct drm_file *file, u32 handle, u32 point)¶: adds a syncobj's fence as a job dependency

Parameters

struct drm_sched_job *job: scheduler job to add the dependencies to
struct drm_file *file: drm file private pointer
u32 handle: syncobj handle to lookup
u32 point: timeline point

Description

This adds the fence matching the given syncobj to job.

Return

0 on success, or an error on failing to expand the array.

int drm_sched_job_add_resv_dependencies(struct drm_sched_job *job, struct dma_resv *resv, enum dma_resv_usage usage)¶: add all fences from the resv to the job

Parameters

struct drm_sched_job *job: scheduler job to add the dependencies to
struct dma_resv *resv: the dma_resv object to get the fences from
enum dma_resv_usage usage: the dma_resv_usage to use to filter the fences

Description

This adds all fences matching the given usage from resv to job. Must be called with the resv lock held.

Return

0 on success, or an error on failing to expand the array.

int drm_sched_job_add_implicit_dependencies(struct drm_sched_job *job, struct drm_gem_object *obj, bool write)¶: adds implicit dependencies as job dependencies

Parameters

struct drm_sched_job *job: scheduler job to add the dependencies to
struct drm_gem_object *obj: the gem object to add new dependencies from.
bool write: whether the job might write the object (so we need to depend on shared fences in the reservation object).

Description

This should be called after drm_gem_lock_reservations() on your array of GEM objects used in the job but before updating the reservations with your own fences.

Return

0 on success, or an error on failing to expand the array.

void drm_sched_job_cleanup(struct drm_sched_job *job)¶: clean up scheduler job resources

Parameters

struct drm_sched_job *job: scheduler job to clean up

Description

Cleans up the resources allocated with drm_sched_job_init().

Drivers should call this from their error unwind code if job is aborted before drm_sched_job_arm() is called.

After that point of no return job is committed to be executed by the scheduler, and this function should be called from the drm_sched_backend_ops.free_job callback.

struct drm_gpu_scheduler *drm_sched_pick_best(struct drm_gpu_scheduler **sched_list, unsigned int num_sched_list)¶: Get a drm sched from a sched_list with the least load

Parameters

struct drm_gpu_scheduler **sched_list: list of drm_gpu_schedulers
unsigned int num_sched_list: number of drm_gpu_schedulers in the sched_list

Description

Returns pointer of the sched with the least load or NULL if none of the drm_gpu_schedulers are ready

int drm_sched_init(struct drm_gpu_scheduler *sched, const struct drm_sched_backend_ops *ops, unsigned hw_submission, unsigned hang_limit, long timeout, struct workqueue_struct *timeout_wq, atomic_t *score, const char *name, struct device *dev)¶: Init a gpu scheduler instance

Parameters

struct drm_gpu_scheduler *sched: scheduler instance
const struct drm_sched_backend_ops *ops: backend operations for this scheduler
unsigned hw_submission: number of hw submissions that can be in flight
unsigned hang_limit: number of times to allow a job to hang before dropping it
long timeout: timeout value in jiffies for the scheduler
struct workqueue_struct *timeout_wq: workqueue to use for timeout work. If NULL, the system_wq is used
atomic_t *score: optional score atomic shared with other schedulers
const char *name: name used for debugging
struct device *dev: target struct device

Description

Return 0 on success, otherwise error code.

void drm_sched_fini(struct drm_gpu_scheduler *sched)¶: Destroy a gpu scheduler

Parameters

struct drm_gpu_scheduler *sched: scheduler instance

Description

Tears down and cleans up the scheduler.

void drm_sched_increase_karma(struct drm_sched_job *bad)¶: Update sched_entity guilty flag

Parameters

struct drm_sched_job *bad: The job guilty of time out

Description

Increment on every hang caused by the 'bad' job. If this exceeds the hang limit of the scheduler then the respective sched entity is marked guilty and jobs from it will not be scheduled further

int drm_sched_entity_init(struct drm_sched_entity *entity, enum drm_sched_priority priority, struct drm_gpu_scheduler **sched_list, unsigned int num_sched_list, atomic_t *guilty)¶: Init a context entity used by scheduler when submit to HW ring.

Parameters

struct drm_sched_entity *entity: scheduler entity to init
enum drm_sched_priority priority: priority of the entity
struct drm_gpu_scheduler **sched_list: the list of drm scheds on which jobs from this entity can be submitted
unsigned int num_sched_list: number of drm sched in sched_list
atomic_t *guilty: atomic_t set to 1 when a job on this queue is found to be guilty causing a timeout

Description

Note that the sched_list must have at least one element to schedule the entity.

For changing priority later on at runtime see drm_sched_entity_set_priority(). For changing the set of schedulers sched_list at runtime see drm_sched_entity_modify_sched().

An entity is cleaned up by callind drm_sched_entity_fini(). See also drm_sched_entity_destroy().

Returns 0 on success or a negative error code on failure.

void drm_sched_entity_modify_sched(struct drm_sched_entity *entity, struct drm_gpu_scheduler **sched_list, unsigned int num_sched_list)¶: Modify sched of an entity

Parameters

struct drm_sched_entity *entity: scheduler entity to init
struct drm_gpu_scheduler **sched_list: the list of new drm scheds which will replace existing entity->sched_list
unsigned int num_sched_list: number of drm sched in sched_list

Description

Note that this must be called under the same common lock for entity as drm_sched_job_arm() and drm_sched_entity_push_job(), or the driver needs to guarantee through some other means that this is never called while new jobs can be pushed to entity.

int drm_sched_entity_error(struct drm_sched_entity *entity)¶: return error of last scheduled job

Parameters

struct drm_sched_entity *entity: scheduler entity to check

Description

Opportunistically return the error of the last scheduled job. Result can change any time when new jobs are pushed to the hw.

long drm_sched_entity_flush(struct drm_sched_entity *entity, long timeout)¶: Flush a context entity

Parameters

struct drm_sched_entity *entity: scheduler entity
long timeout: time to wait in for Q to become empty in jiffies.

Description

Splitting drm_sched_entity_fini() into two functions, The first one does the waiting, removes the entity from the runqueue and returns an error when the process was killed.

Returns the remaining time in jiffies left from the input timeout

void drm_sched_entity_fini(struct drm_sched_entity *entity)¶: Destroy a context entity

Parameters

struct drm_sched_entity *entity: scheduler entity

Description

Cleanups up entity which has been initialized by drm_sched_entity_init().

If there are potentially job still in flight or getting newly queued drm_sched_entity_flush() must be called first. This function then goes over the entity and signals all jobs with an error code if the process was killed.

void drm_sched_entity_destroy(struct drm_sched_entity *entity)¶: Destroy a context entity

Parameters

struct drm_sched_entity *entity: scheduler entity

Description

Calls drm_sched_entity_flush() and drm_sched_entity_fini() as a convenience wrapper.

void drm_sched_entity_set_priority(struct drm_sched_entity *entity, enum drm_sched_priority priority)¶: Sets priority of the entity

Parameters

struct drm_sched_entity *entity: scheduler entity
enum drm_sched_priority priority: scheduler priority

Description

Update the priority of runqueus used for the entity.

void drm_sched_entity_push_job(struct drm_sched_job *sched_job)¶: Submit a job to the entity's job queue

Parameters

struct drm_sched_job *sched_job: job to submit

Note

To guarantee that the order of insertion to queue matches the job's fence sequence number this function should be called with drm_sched_job_arm() under common lock for the struct drm_sched_entity that was set up for sched_job in drm_sched_job_init().

Description

Returns 0 for success, negative error code otherwise.

DRM Memory Management¶

The Translation Table Manager (TTM)¶

TTM device object reference¶

TTM resource placement reference¶

TTM resource object reference¶

TTM TT object reference¶

TTM page pool reference¶

The Graphics Execution Manager (GEM)¶

GEM Initialization¶

GEM Objects Creation¶

GEM Objects Lifetime¶

GEM Objects Naming¶

GEM Objects Mapping¶

Memory Coherency¶

Command Execution¶

GEM Function Reference¶

GEM DMA Helper Functions Reference¶

GEM SHMEM Helper Function Reference¶

GEM VRAM Helper Functions Reference¶

GEM TTM Helper Functions Reference¶

VMA Offset Manager¶

PRIME Buffer Sharing¶

Overview and Lifetime Rules¶

Reference Counting for GEM Drivers¶

PRIME Helper Functions¶

Exporting buffers¶

Importing buffers¶

PRIME Function References¶

DRM MM Range Allocator¶

Overview¶

LRU Scan/Eviction Support¶

DRM MM Range Allocator Function References¶

DRM GPU VA Manager¶

Overview¶

Split and Merge¶

Locking¶

Examples¶

DRM GPU VA Manager Function References¶

DRM Buddy Allocator¶

DRM Buddy Function References¶

DRM Cache Handling and Fast WC memcpy()¶

DRM Sync Objects¶

Host-side wait on syncobjs¶

Import/export of syncobjs¶

Import/export of timeline points in timeline syncobjs¶

DRM Execution context¶

GPU Scheduler¶

Overview¶

Scheduler Function References¶