Re: [PATCH v4 2/2] drm/amd: use fixed dsc bits-per-pixel from edid

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 16 Oct 2025, Yaroslav Bolyukin <iam@lach.pw> wrote:
> VESA vendor header from DisplayID spec may contain fixed bit per pixel
> rate, it should be respected by drm driver
>
> Signed-off-by: Yaroslav Bolyukin <iam@lach.pw>
> ---
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> 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 0d03e324d5b9..ebe5bb4eecf8 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -6521,6 +6521,11 @@ static void fill_stream_properties_from_drm_display_mode(
>  
>  	stream->output_color_space = get_output_color_space(timing_out, connector_state);
>  	stream->content_type = get_output_content_type(connector_state);
> +
> +	/* DisplayID Type VII pass-through timings. */
> +	if (mode_in->dsc_passthrough_timings_support && info->dp_dsc_bpp != 0) {
> +		stream->timing.dsc_fixed_bits_per_pixel_x16 = info->dp_dsc_bpp;
> +	}

If we had mode->dp_dsc_bpp_x16 directly, or something better named, this
would be simpler. This will eventually be replicated in a bunch of
drivers.

BR,
Jani.

>  }
>  
>  static void fill_audio_info(struct audio_info *audio_info,
> @@ -7067,6 +7072,13 @@ create_stream_for_sink(struct drm_connector *connector,
>  					&mode, preferred_mode, scale);
>  
>  			preferred_refresh = drm_mode_vrefresh(preferred_mode);
> +
> +			/*
> +			 * HACK: In case of multiple supported modes, we should look at the matching mode to decide this flag.
> +			 * But what is matching mode, how should it be decided?
> +			 * Assuming that only preferred mode would have this flag.
> +			 */
> +			mode.dsc_passthrough_timings_support = preferred_mode->dsc_passthrough_timings_support;
>  		}
>  	}
>  
> @@ -7756,7 +7768,7 @@ create_validate_stream_for_sink(struct drm_connector *connector,
>  			drm_dbg_kms(connector->dev, "%s:%d Validation failed with %d, retrying w/ YUV420\n",
>  				    __func__, __LINE__, dc_result);
>  			aconnector->force_yuv420_output = true;
> -		}
> +}
>  		stream = create_validate_stream_for_sink(connector, drm_mode,
>  							 dm_state, old_stream);
>  		aconnector->force_yuv422_output = false;

-- 
Jani Nikula, Intel