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+.. _vkms:
+
+==========================================
+ drm/vkms Virtual Kernel Modesetting
+==========================================
+
+.. kernel-doc:: drivers/gpu/drm/vkms/vkms_drv.c
+   :doc: vkms (Virtual Kernel Modesetting)
+
+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).
+
+- 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.
+
+Add Plane Features
+------------------
+
+There's lots of plane features we could add support for:
+
+- Real overlay planes, not just cursor.
+
+- Full alpha blending on all planes.
+
+- Rotation, scaling.
+
+- 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).
+
+For all of these, we also want to review the igt test coverage and make sure all
+relevant igt testcases work on vkms.
+
+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:
+
+- Writeback connector. This is useful for testing compositors if you don't have
+  hardware with writeback support.
+
+- 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
+---------------
+
+- Variable refresh rate/freesync support. This probably needs prime buffer
+  sharing support, so that we can use vgem fences to simulate rendering in
+  testing. Also needs support to specify the EDID.
+
+- 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".
+
+Atomic Check using eBPF
+-----------------------
+
+Atomic drivers have lots of restrictions which are not exposed to userspace in
+any explicit form through e.g. possible property values. Userspace can only
+inquiry about these limits through the atomic IOCTL, possibly using the
+TEST_ONLY flag. Trying to add configurable code for all these limits, to allow
+compositors to be tested against them, would be rather futile exercise. Instead
+we could add support for eBPF to validate any kind of atomic state, and
+implement a library of different restrictions.
+
+This needs a bunch of features (plane compositing, multiple outputs, ...)
+enabled already to make sense.