RTX 6800 XT 4K120 problems

[Alex Deucher]

On Wed, Apr 21, 2021 at 5:35 PM Julian Picht
<julian.picht+amdgfx at gmail.com> wrote:
>
> Hi all,
>
> I recently purchased a 4K120Hz display and am currently trying to get it fully working. It's connected via HDMI 2.1, because it does not have a DisplayPort input.
>
> I'm on 5.12-rc8, and it seems that the modes are not detected correctly, the driver defaults to YCbCr modes (with chroma sub-sampling) which makes everything look weird, blocky and broken.
>
> I've patched in a debug fs flag to force RGB-mode which works fine up to 4k60, anything higher and the display detects the signal as YCbCr anyways (false color mode looks interesting, but not very useful).
>
> I've tested the GPU+display combination on W10 - works fine up to 4K120 HDR (RGB 10Bit).
>
> I'm happy to help implementing / fixing this.
>
> My current suspects are: pixel clock limitations, and edid parser. Can anyone tell me if I'm on the right track? Would me trying to do this interfere with anything else that somebody is working on?
>

HDMI 2.1 is not supported in open source drivers due to the fact that
HDMI Forum does not make the 2.1 spec publicly available.  There is
not much we can do until that changes.

Alex