3 ==========================================
4 drm/vkms Virtual Kernel Modesetting
5 ==========================================
7 .. kernel-doc:: drivers/gpu/drm/vkms/vkms_drv.c
8 :doc: vkms (Virtual Kernel Modesetting)
16 - Optimize CRC computation ``compute_crc()`` and plane blending ``blend()``
18 - Use the alpha value to blend vaddr_src with vaddr_dst instead of
19 overwriting it in ``blend()``.
21 - Add igt test to check cleared alpha value for XRGB plane format.
23 - Add igt test to check extreme alpha values i.e. fully opaque and fully
24 transparent (intermediate values are affected by hw-specific rounding modes).
29 Some IGT test cases are failing. Need to analyze why and fix the issues:
31 - plain-flip-fb-recreate
33 - flip-vs-blocking-wf-vblank
34 - plain-flip-fb-recreate-interruptible
35 - flip-vs-wf_vblank-interruptible
40 We want to be able to reconfigure vkms instance without having to reload the
41 module. Use/Test-cases:
43 - Hotplug/hotremove connectors on the fly (to be able to test DP MST handling of
46 - Configure planes/crtcs/connectors (we'd need some code to have more than 1 of
49 - Change output configuration: Plug/unplug screens, change EDID, allow changing
52 The currently proposed solution is to expose vkms configuration through
53 configfs. All existing module options should be supported through configfs too.
58 There's lots of plane features we could add support for:
60 - Real overlay planes, not just cursor.
62 - Full alpha blending on all planes.
66 - Additional buffer formats, especially YUV formats for video like NV12.
67 Low/high bpp RGB formats would also be interesting.
69 - Async updates (currently only possible on cursor plane using the legacy cursor
72 For all of these, we also want to review the igt test coverage and make sure all
73 relevant igt testcases work on vkms.
78 Currently vkms only computes a CRC for each frame. Once we have additional plane
79 features, we could write back the entire composited frame, and expose it as:
81 - Writeback connector. This is useful for testing compositors if you don't have
82 hardware with writeback support.
84 - As a v4l device. This is useful for debugging compositors on special vkms
85 configurations, so that developers see what's really going on.
90 We already have vgem, which is a gem driver for testing rendering, similar to
91 how vkms is for testing the modeset side. Adding buffer sharing support to vkms
92 allows us to test them together, to test synchronization and lots of other
93 features. Also, this allows compositors to test whether they work correctly on
94 SoC chips, where the display and rendering is very often split between 2
100 - Variable refresh rate/freesync support. This probably needs prime buffer
101 sharing support, so that we can use vgem fences to simulate rendering in
102 testing. Also needs support to specify the EDID.
104 - Add support for link status, so that compositors can validate their runtime
105 fallbacks when e.g. a Display Port link goes bad.
107 - All the hotplug handling describe under "Runtime Configuration".
109 Atomic Check using eBPF
110 -----------------------
112 Atomic drivers have lots of restrictions which are not exposed to userspace in
113 any explicit form through e.g. possible property values. Userspace can only
114 inquiry about these limits through the atomic IOCTL, possibly using the
115 TEST_ONLY flag. Trying to add configurable code for all these limits, to allow
116 compositors to be tested against them, would be rather futile exercise. Instead
117 we could add support for eBPF to validate any kind of atomic state, and
118 implement a library of different restrictions.
120 This needs a bunch of features (plane compositing, multiple outputs, ...)
121 enabled already to make sense.