RTX 6800 XT 4K120 problems

[Julian Picht]

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?

Cheers,
Julian Picht
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