drm/mcde ST-Ericsson MCDE Multi-channel display engineΒΆ

The MCDE (short for multi-channel display engine) is a graphics controller found in the Ux500 chipsets, such as NovaThor U8500. It was initially conceptualized by ST Microelectronics for the successor of the Nomadik line, STn8500 but productified in the ST-Ericsson U8500 where is was used for mass-market deployments in Android phones from Samsung and Sony Ericsson.

It can do 1080p30 on SDTV CCIR656, DPI-2, DBI-2 or DSI for panels with or without frame buffering and can convert most input formats including most variants of RGB and YUV.

The hardware has four display pipes, and the layout is a little bit like this:

Memory     -> Overlay -> Channel -> FIFO -> 8 formatters -> DSI/DPI
External      0..5       0..3       A,B,    6 x DSI         bridge
source 0..9                         C0,C1   2 x DPI

FIFOs A and B are for LCD and HDMI while FIFO CO/C1 are for panels with embedded buffer. 6 of the formatters are for DSI, 3 pairs for VID/CMD respectively. 2 of the formatters are for DPI.

Behind the formatters are the DSI or DPI ports that route to the external pins of the chip. As there are 3 DSI ports and one DPI port, it is possible to configure up to 4 display pipelines (effectively using channels 0..3) for concurrent use.

In the current DRM/KMS setup, we use one external source, one overlay, one FIFO and one formatter which we connect to the simple DMA framebuffer helpers. We then provide a bridge to the DSI port, and on the DSI port bridge we connect hang a panel bridge or other bridge. This may be subject to change as we exploit more of the hardware capabilities.

TODO:

  • Enabled damaged rectangles using drm_plane_enable_fb_damage_clips() so we can selectively just transmit the damaged area to a command-only display.

  • Enable mixing of more planes, possibly at the cost of moving away from using the simple framebuffer pipeline.

  • Enable output to bridges such as the AV8100 HDMI encoder from the DSI bridge.