drm/vkms: update todo

TODO

====

CRC API Improvements

--------------------

- Optimize CRC computation ``compute_crc()`` and plane blending ``blend()``

- Use the alpha value to blend vaddr_src with vaddr_dst instead of

  overwriting it in ``blend()``.

- Add igt test to check cleared alpha value for XRGB plane format.

- Add igt test to check extreme alpha values i.e. fully opaque and fully

  transparent (intermediate values are affected by hw-specific rounding modes).

Runtime Configuration

---------------------

We want to be able to reconfigure vkms instance without having to reload the

module. Use/Test-cases:

- Hotplug/hotremove connectors on the fly (to be able to test DP MST handling of

  compositors).

If you want to do any of the items listed below, please share your interest

with VKMS maintainers.

- Configure planes/crtcs/connectors (we'd need some code to have more than 1 of

  them first).

IGT better support

------------------

- Change output configuration: Plug/unplug screens, change EDID, allow changing

  the refresh rate.

- Investigate: (1) test cases on kms_plane that are failing due to timeout on

  capturing CRC; (2) when running kms_flip test cases in sequence, some

  successful individual test cases are failing randomly.

The currently proposed solution is to expose vkms configuration through

configfs.  All existing module options should be supported through configfs too.

- VKMS already has support for vblanks simulated via hrtimers, which can be

  tested with kms_flip test; in some way, we can say that VKMS already mimics

  the real hardware vblank. However, we also have virtual hardware that does

  not support vblank interrupt and completes page_flip events right away; in

  this case, compositor developers may end up creating a busy loop on virtual

  hardware. It would be useful to support Virtual Hardware behavior in VKMS

  because this can help compositor developers to test their features in

  multiple scenarios.

Add Plane Features

------------------

- Additional buffer formats, especially YUV formats for video like NV12.

  Low/high bpp RGB formats would also be interesting.

- Async updates (currently only possible on cursor plane using the legacy cursor

  api).

- Async updates (currently only possible on cursor plane using the legacy

  cursor api).

For all of these, we also want to review the igt test coverage and make sure

all relevant igt testcases work on vkms.

Prime Buffer Sharing

--------------------

For all of these, we also want to review the igt test coverage and make sure all

relevant igt testcases work on vkms.

- Syzbot report - WARNING in vkms_gem_free_object:

  https://syzkaller.appspot.com/bug?extid=e7ad70d406e74d8fc9d0

Runtime Configuration

---------------------

We want to be able to reconfigure vkms instance without having to reload the

module. Use/Test-cases:

- Hotplug/hotremove connectors on the fly (to be able to test DP MST handling

  of compositors).

- Configure planes/crtcs/connectors (we'd need some code to have more than 1 of

  them first).

- Change output configuration: Plug/unplug screens, change EDID, allow changing

  the refresh rate.

The currently proposed solution is to expose vkms configuration through

configfs.  All existing module options should be supported through configfs

too.

Writeback support

-----------------

Currently vkms only computes a CRC for each frame. Once we have additional plane

features, we could write back the entire composited frame, and expose it as:

- The writeback and CRC capture operations share the use of composer_enabled

  boolean to ensure vblanks. Probably, when these operations work together,

  composer_enabled needs to refcounting the composer state to proper work.

- Writeback connector. This is useful for testing compositors if you don't have

  hardware with writeback support.

- Add support for cloned writeback outputs and related test cases using a

  cloned output in the IGT kms_writeback.

- As a v4l device. This is useful for debugging compositors on special vkms

  configurations, so that developers see what's really going on.

Prime Buffer Sharing

--------------------

We already have vgem, which is a gem driver for testing rendering, similar to

how vkms is for testing the modeset side. Adding buffer sharing support to vkms

allows us to test them together, to test synchronization and lots of other

features. Also, this allows compositors to test whether they work correctly on

SoC chips, where the display and rendering is very often split between 2

drivers.

Output Features

---------------

- Add support for link status, so that compositors can validate their runtime

  fallbacks when e.g. a Display Port link goes bad.

- All the hotplug handling describe under "Runtime Configuration".

CRC API Improvements

--------------------

- Optimize CRC computation ``compute_crc()`` and plane blending ``blend()``

Atomic Check using eBPF

-----------------------