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

[Stefan Bader]

On 28.04.21 09:16, Krzysztof Kozlowski wrote:
> 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.

Not necessarily, the place for the SRU justification is mainly the bug report. A 
cover email can repeat that but could also be a less formal explanation for 
reviewers. The SRU justification is geared for non-developers (potentially). 
However, correct is that the patch itself should be the cherry picked / 
backported form with only BugLink, cherry picked/backported from, and 
signed-off-by added. Note that BugLink is preferred to use the: 
https://bugs.launchpad.net/bugs/<number> form.

-Stefan
> 
> 
> Best regards,
> Krzysztof
> 


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