[RFC 0/4] Atomic Display Framework

Greg Hackmann ghackmann at google.com
Wed Aug 28 18:51:17 PDT 2013


ADF is an experimental display framework that I designed after experimenting with a KMS-based hardware composer for Android.  ADF started as an proof-of-concept implemented from scratch, so right now it's a separate framework rather than a patchstack on top of KMS.  If there's community interest, moving forward I'd like to merge its functionality into KMS rather than keep it as a separate thing.

I'm going to talk about ADF at the Android and Graphics session at Linux Plumbers.  The documentation's not done but I wanted to post these patches to people a heads-up about ADF.  If there's interest I can write up some more formal documentation ahead of Plumbers.

I designed ADF to deal with some serious issues I had working with KMS:

1.  The API is geared toward updating one object at a time.  Android's graphics stack needs the entire screen updated atomically to avoid tearing, and on some SoCs to avoid wedging the display hardware.  Rob Clark's atomic modeset patchset worked, but copy/update/commit design meant the driver had to keep a lot more internal state.

2.  Some SoCs don't map well to KMS's CRTC + planes + encoders + connector model.  At the time I was dealing with hardware where the blending engines didn't have their own framebuffer (they could only scan out constant colors or mix the output of other blocks), and you needed to gang several mixers together to drive high-res displays.

3.  KMS doesn't support custom pixel formats, which a lot of newer SoCs use internally to cut down on bandwidth between hardware blocks. 

4.  KMS doesn't have a way to exchange sync fences.  As a hack I managed to pass sync fences into the kernel as properties of the atomic pageflip, but there was no good way to get them back out of the kernel without a side channel.

ADF represents display devices as collections of overlay engines and interfaces.  Overlay engines (struct adf_overlay_engine) scan out images and interfaces (struct adf_interface) display those images.  Overlay engines and interfaces can be connected in any n-to-n configuration that the hardware supports.

Clients issue atomic updates to the screen by passing in a list of buffers (struct adf_buffer) consisting of dma-buf handles, sync fences, and basic metadata like format and size.  If this involves composing multiple buffers, clients include a block of custom data describing the actual composition (scaling, z-order, blending, etc.) in a driver-specific format.

Drivers provide hooks to validate these custom data blocks and commit the new configuration to hardware.  ADF handles importing the dma-bufs and fences, waiting on incoming sync fences before committing, advancing the display's sync timeline, and releasing dma-bufs once they're removed from the screen.

ADF represents pixel formats using DRM-style fourccs, and automatically sanity-checks buffer sizes when using one of the formats listed in drm_fourcc.h.  Drivers can support custom fourccs if they provide hooks to validate buffers that use them.

ADF also provides driver hooks for modesetting, managing and reporting hardware events like vsync, and changing DPMS state.  These are documented in struct adf_{obj,overlay_engine,interface,device}_ops, and are similar to the equivalent DRM ops.

Greg Hackmann (3):
  video: add atomic display framework
  video: adf: add display core helper
  video: adf: add memblock helper

Laurent Pinchart (1):
  video: Add generic display entity core

 drivers/video/Kconfig                |    2 +
 drivers/video/Makefile               |    2 +
 drivers/video/adf/Kconfig            |   15 +
 drivers/video/adf/Makefile           |   14 +
 drivers/video/adf/adf.c              | 1013 ++++++++++++++++++++++++++++++++++
 drivers/video/adf/adf.h              |   49 ++
 drivers/video/adf/adf_client.c       |  853 ++++++++++++++++++++++++++++
 drivers/video/adf/adf_display.c      |  123 +++++
 drivers/video/adf/adf_fops.c         |  982 ++++++++++++++++++++++++++++++++
 drivers/video/adf/adf_fops.h         |   37 ++
 drivers/video/adf/adf_fops32.c       |  217 ++++++++
 drivers/video/adf/adf_fops32.h       |   78 +++
 drivers/video/adf/adf_memblock.c     |  150 +++++
 drivers/video/adf/adf_sysfs.c        |  291 ++++++++++
 drivers/video/adf/adf_sysfs.h        |   33 ++
 drivers/video/adf/adf_trace.h        |   93 ++++
 drivers/video/display/Kconfig        |    4 +
 drivers/video/display/Makefile       |    1 +
 drivers/video/display/display-core.c |  362 ++++++++++++
 include/video/adf.h                  |  743 +++++++++++++++++++++++++
 include/video/adf_client.h           |   61 ++
 include/video/adf_display.h          |   31 ++
 include/video/adf_format.h           |  282 ++++++++++
 include/video/adf_memblock.h         |   20 +
 include/video/display.h              |  150 +++++
 25 files changed, 5606 insertions(+)
 create mode 100644 drivers/video/adf/Kconfig
 create mode 100644 drivers/video/adf/Makefile
 create mode 100644 drivers/video/adf/adf.c
 create mode 100644 drivers/video/adf/adf.h
 create mode 100644 drivers/video/adf/adf_client.c
 create mode 100644 drivers/video/adf/adf_display.c
 create mode 100644 drivers/video/adf/adf_fops.c
 create mode 100644 drivers/video/adf/adf_fops.h
 create mode 100644 drivers/video/adf/adf_fops32.c
 create mode 100644 drivers/video/adf/adf_fops32.h
 create mode 100644 drivers/video/adf/adf_memblock.c
 create mode 100644 drivers/video/adf/adf_sysfs.c
 create mode 100644 drivers/video/adf/adf_sysfs.h
 create mode 100644 drivers/video/adf/adf_trace.h
 create mode 100644 drivers/video/display/Kconfig
 create mode 100644 drivers/video/display/Makefile
 create mode 100644 drivers/video/display/display-core.c
 create mode 100644 include/video/adf.h
 create mode 100644 include/video/adf_client.h
 create mode 100644 include/video/adf_display.h
 create mode 100644 include/video/adf_format.h
 create mode 100644 include/video/adf_memblock.h
 create mode 100644 include/video/display.h


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