[PATCH] drm/amd/display: Try YCbCr420 color when YCbCr444 fails

[Alex Deucher]

On Wed, Mar 17, 2021 at 11:25 AM Werner Sembach <wse at tuxedocomputers.com> wrote:
>
> When encoder validation of a display mode fails, retry with less bandwidth
> heavy YCbCr420 color mode, if available. This enables some HDMI 1.4 setups
> to support 4k60Hz output, which previously failed silently.
>
> 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. This patch fixes the problem by retrying
> to find a display mode with YCbCr420 enforced and using it, if it is
> valid.
>
> Signed-off-by: Werner Sembach <wse at tuxedocomputers.com>
> Cc: <stable at vger.kernel.org>


This seems reasonable to me.  Harry, Leo, Any objections?

Alex

> ---
>
> From c9398160caf4ff20e63b8ba3a4366d6ef95c4ac3 Mon Sep 17 00:00:00 2001
> From: Werner Sembach <wse at tuxedocomputers.com>
> Date: Wed, 17 Mar 2021 12:52:22 +0100
> 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 961abf1cf040..2d16389b5f1e 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -5727,6 +5727,15 @@ 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;
>  }
>
> --
> 2.25.1
>
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