[PATCH 10/24] drm/amd/display: Rework CRTC color management

Michel Dänzer michel at daenzer.net
Fri Jun 7 15:51:22 UTC 2019

On 2019-06-07 2:26 p.m., Kazlauskas, Nicholas wrote:
> On 6/7/19 3:58 AM, Michel Dänzer wrote:
>> On 2019-06-06 10:54 p.m., Bhawanpreet Lakha wrote:
>>> From: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
>>> [Why]
>>> To prepare for the upcoming DRM plane color management properties
>>> we need to correct a lot of wrong behavior and assumptions made for
>>> CRTC color management.
>>> The documentation added by this commit in amdgpu_dm_color explains
>>> how the HW color pipeline works and its limitations with the DRM
>>> interface.
>>> The current implementation does the following wrong:
>>> - Implicit sRGB DGM when no CRTC DGM is set
>>> - Implicit sRGB RGM when no CRTC RGM is set
>>> - No way to specify a non-linear DGM matrix that produces correct output
>>> - No way to specify a correct RGM when a linear DGM is used
>>> We had workarounds for passing kms_color tests but not all of the
>>> behavior we had wrong was covered by these tests (especially when
>>> it comes to non-linear DGM). Testing both DGM and RGM at the same time
>>> isn't something kms_color tests well either.
>>> [How]
>>> The specifics for how color management works in AMDGPU and the new
>>> behavior can be found by reading the documentation added to
>>> amdgpu_dm_color.c from this patch.
>>> All of the incorrect cases from the old implementation have been
>>> addressed for the atomic interface, but there still a few TODOs for
>>> the legacy one.
>>> Note: this does cause regressions for kms_color at pipe-a-ctm-* over HDMI.
>>> The result looks correct from visual inspection but the CRC no longer
>>> matches. For reference, the test was previously doing the following:
>>> linear degamma -> CTM -> sRGB regamma -> RGB to YUV (709) -> ...
>>> Now the test is doing:
>>> linear degamma -> CTM -> linear regamma -> RGB to YUV (709) -> ...
>>> Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
>>> Reviewed-by: Sun peng Li <Sunpeng.Li at amd.com>
>>> Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha at amd.com>
>> Does this address https://bugs.freedesktop.org/110677 ? If so, can you
>> add a reference to the commit log?
> It unfortunately does not. There are still some remaining issues with 
> legacy gamma support that I intend to address at some point - which I 
> left in this patch as TODOs.

Note that the bug reporter is using xf86-video-amdgpu, which no longer
uses legacy gamma with DC, unless I misunderstand what you mean by that.

Earthling Michel Dänzer               |              https://www.amd.com
Libre software enthusiast             |             Mesa and X developer

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