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

[Stefan Bader]

On 27.04.21 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>
> ---

For formal reasons mentioned in other replies. Oh, and also note that the 
targets would be hirsute:linux and groovy:linux or just short [SRU G/H]. The hwe 
kernels are based on those and any change the hwe kernels get usually must go 
into the parent kernels, too.

-Stefan

> 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
> 
> ---
>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> 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 ad4afbc37d51..efa12ad4da72 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -5738,6 +5738,15 @@ create_validate_stream_for_sink(struct amdgpu_dm_connector *aconnector,
>   
>   	} while (stream == NULL && requested_bpc >= 6);
>   
> +	if (dc_result == DC_FAIL_ENC_VALIDATE && !aconnector->force_yuv420_output) {
> +		DRM_DEBUG_KMS("Retry forcing YCbCr420 encoding\n");
> +
> +		aconnector->force_yuv420_output = true;
> +		stream = create_validate_stream_for_sink(aconnector, drm_mode,
> +						dm_state, old_stream);
> +		aconnector->force_yuv420_output = false;
> +	}
> +
>   	return stream;
>   }
>   
> 


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