t7xx driver for MTK PCIe based T700 5G modem

The t7xx driver is a WWAN PCIe host driver developed for linux or Chrome OS platforms for data exchange over PCIe interface between Host platform & MediaTek's T700 5G modem. The driver exposes an interface conforming to the MBIM protocol [1]. Any front end application (e.g. Modem Manager) could easily manage the MBIM interface to enable data communication towards WWAN. The driver also provides an interface to interact with the MediaTek's modem via AT commands.

Basic usage

MBIM & AT functions are inactive when unmanaged. The t7xx driver provides WWAN port userspace interfaces representing MBIM & AT control channels and does not play any role in managing their functionality. It is the job of a userspace application to detect port enumeration and enable MBIM & AT functionalities.

Examples of few such userspace applications are:

  • mbimcli (included with the libmbim [2] library), and

  • Modem Manager [3]

Management Applications to carry out below required actions for establishing MBIM IP session:

  • open the MBIM control channel

  • configure network connection settings

  • connect to network

  • configure IP network interface

Management Applications to carry out below required actions for send an AT command and receive response:

  • open the AT control channel using a UART tool or a special user tool

Management application development

The driver and userspace interfaces are described below. The MBIM protocol is described in [1] Mobile Broadband Interface Model v1.0 Errata-1.

MBIM control channel userspace ABI

/dev/wwan0mbim0 character device

The driver exposes an MBIM interface to the MBIM function by implementing MBIM WWAN Port. The userspace end of the control channel pipe is a /dev/wwan0mbim0 character device. Application shall use this interface for MBIM protocol communication.

Fragmentation

The userspace application is responsible for all control message fragmentation and defragmentation as per MBIM specification.

/dev/wwan0mbim0 write()

The MBIM control messages from the management application must not exceed the negotiated control message size.

/dev/wwan0mbim0 read()

The management application must accept control messages of up the negotiated control message size.

MBIM data channel userspace ABI

wwan0-X network device

The t7xx driver exposes IP link interface "wwan0-X" of type "wwan" for IP traffic. Iproute network utility is used for creating "wwan0-X" network interface and for associating it with MBIM IP session.

The userspace management application is responsible for creating new IP link prior to establishing MBIM IP session where the SessionId is greater than 0.

For example, creating new IP link for a MBIM IP session with SessionId 1:

ip link add dev wwan0-1 parentdev wwan0 type wwan linkid 1

The driver will automatically map the "wwan0-1" network device to MBIM IP session 1.

AT port userspace ABI

/dev/wwan0at0 character device

The driver exposes an AT port by implementing AT WWAN Port. The userspace end of the control port is a /dev/wwan0at0 character device. Application shall use this interface to issue AT commands.

The MediaTek's T700 modem supports the 3GPP TS 27.007 [4] specification.

References

[1] MBIM (Mobile Broadband Interface Model) Errata-1

[2] libmbim "a glib-based library for talking to WWAN modems and devices which speak the Mobile Interface Broadband Model (MBIM) protocol"

[3] Modem Manager "a DBus-activated daemon which controls mobile broadband (2G/3G/4G/5G) devices and connections"

[4] Specification # 27.007 - 3GPP