[PATCH v2 18/21] drm/amd/display: Fallback to 2020_YCBCR if the pixel encoding is not RGB

[Joshua Ashton]

On 1/23/23 20:30, Sebastian Wick wrote:
> A new property to control YCC and subsampling would be the more
> complete path here. If we actually want to fix this in the short-term
> though, we should handle the YCC and RGB Colorspace values as
> equivalent, everywhere. Technically we're breaking the user space API
> here so it should be documented on the KMS property and other drivers
> must be adjusted accordingly as well.

I am happy with treating 2020_YCC and 2020_RGB as the same.

I think having the YCC/RGB split here in Colorspace is a mistake.
Pixel encoding should be completely separate from colorspace from a uAPI 
perspective when we want to expose that.
It's just a design flaw from when it was added as it just mirrors the 
values in the colorimetry packets 1:1. I understand why this happened, 
and I don't think it's a big deal for us to correct ourselves now:

I suggest we deprecate the _YCC variants, treat them the same as the RGB 
enum to avoid any potential uAPI breakage and key the split entirely off 
the pixel_encoding value.

That way when we do want to plumb more explicit pixel encoding down the 
line, userspace only has to manage one thing. There's no advantage for 
anything more here.

- Joshie 🐸✨

> 
> On Fri, Jan 13, 2023 at 5:26 PM Harry Wentland <harry.wentland at amd.com> wrote:
>>
>> From: Joshua Ashton <joshua at froggi.es>
>>
>> Userspace might not aware whether we're sending RGB or YCbCr
>> data to the display. If COLOR_SPACE_2020_RGB_FULLRANGE is
>> requested but the output encoding is YCbCr we should
>> send COLOR_SPACE_2020_YCBCR.
>>
>> Signed-off-by: Joshua Ashton <joshua at froggi.es>
>> Signed-off-by: Harry Wentland <harry.wentland at amd.com>
>> Cc: Pekka Paalanen <ppaalanen at gmail.com>
>> Cc: Sebastian Wick <sebastian.wick at redhat.com>
>> Cc: Vitaly.Prosyak at amd.com
>> Cc: Joshua Ashton <joshua at froggi.es>
>> Cc: dri-devel at lists.freedesktop.org
>> Cc: amd-gfx at lists.freedesktop.org
>> Reviewed-by: Harry Wentland <harry.wentland at amd.com>
>> ---
>>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> index f74b125af31f..16940ea61b59 100644
>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> @@ -5184,7 +5184,10 @@ get_output_color_space(const struct dc_crtc_timing *dc_crtc_timing,
>>                  color_space = COLOR_SPACE_ADOBERGB;
>>                  break;
>>          case DRM_MODE_COLORIMETRY_BT2020_RGB:
>> -               color_space = COLOR_SPACE_2020_RGB_FULLRANGE;
>> +               if (dc_crtc_timing->pixel_encoding == PIXEL_ENCODING_RGB)
>> +                       color_space = COLOR_SPACE_2020_RGB_FULLRANGE;
>> +               else
>> +                       color_space = COLOR_SPACE_2020_YCBCR;
>>                  break;
>>          case DRM_MODE_COLORIMETRY_BT2020_YCC:
>>                  color_space = COLOR_SPACE_2020_YCBCR;
>> --
>> 2.39.0
>>
>