[PATCH][SRU][HWE-5.8/HWE-5.11] Make AMD gpus choose YCbCr420 encoding automatically when required for 4k 60Hz output

[Krzysztof Kozlowski]

On 27/04/2021 18:45, Werner Sembach wrote:
> BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1922754
> 
> SRU Justification:
> 
> Impact:
> On some setups, while the monitor and the gpu support display modes with pixel
> clocks of up to 600MHz, the link encoder might not. This prevents YCbCr444 and
> RGB encoding for 4k60Hz, but YCbCr420 encoding might still be possible. However,
> which color mode is used is decided before the link encoder capabilities are
> checked, causing the check to fail and discarding 4k60Hz from the list of
> possible display modes.
> 
> Fix:
> This patch fixes the problem by retrying to find a display mode with YCbCr420
> enforced and using it, if it is valid.
> 
> Testcase:
> Tested on an Clevo NL50RU. General: Find a PC with a current AMD Radeon GPU, but
> only a hdmi 1.4 output (e.g. current Clevo laptops with AMD APU's). Connect a
> 4k at 60Hz display supporting YCbCr420 encoding to the hdmi port. Without the patch
> the maximum that can be set via xrandr is 3840 × 2160 30Hz. With the Patch
> 3840 × 2160 60Hz can be selected which will use YCbCr420 automatically.
> 
> Patch already got accepted upstream for linux-next:
> https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=14e4a095b29fd290a9b80f6e553adcfcf01672d1
> and applies without modifications to ubuntu-focal/hwe-5.8 and hwe-5.11
> 
> Commit-hash: 14e4a095b29fd290a9b80f6e553adcfcf01672d1
> 
> Signed-off-by: Werner Sembach <wse at tuxedocomputers.com>
> ---
> Resend because git send-mail cut off BugLink for some reason
> 
> From 87afe9a830b44bbf42c3a2a7330bc76275bbca32 Mon Sep 17 00:00:00 2001
> From: Werner Sembach <wse at tuxedocomputers.com>
> Date: Tue, 27 Apr 2021 18:29:53 +0200
> Subject: [PATCH] Retry forcing YCbCr420 color on failed encoder validation

Hi,

You need to send the cherry-picked patch from upstream. The SRU
justifications comes as cover letter.


Best regards,
Krzysztof