Re: [Intel-gfx] [PATCH v10 03/13] drm/i915/dp: Add Scaler constraint for YCbCr420 output

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Feb 27, 2023 at 09:33:14AM +0530, Ankit Nautiyal wrote:
> For YCbCr420 output, scaler is required for downsampling.
> Scaler can be used only when source size smaller than max_src_w and
> max_src_h as defined by for the platform.
> So go for native YCbCr420 only if there are no scaler constraints.
> 
> v2: Corrected max-width based on Display Version.
> 
> v3: Updated max-width as per latest Bspec change.
> 
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 41 ++++++++++++++++++++++---
>  1 file changed, 37 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 1a30cc021b25..e95fc0f0d13a 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -804,11 +804,36 @@ u8 intel_dp_dsc_get_slice_count(struct intel_dp *intel_dp,
>  	return 0;
>  }
>  
> +static bool
> +ycbcr420_scaler_constraints(struct drm_i915_private *i915,
> +			    const struct drm_display_mode *mode)
> +{
> +	int max_src_w, max_src_h;
> +
> +	if (DISPLAY_VER(i915) < 11) {
> +		max_src_w = 4096;
> +		max_src_h = 4096;
> +	} else if (DISPLAY_VER(i915) < 12) {
> +		max_src_w = 5120;
> +		max_src_h = 4096;
> +	} else if (DISPLAY_VER(i915) < 14) {
> +		max_src_w = 5120;
> +		max_src_h = 8192;
> +	} else {
> +		max_src_w = 4096;
> +		max_src_h = 8192;
> +	}
> +
> +	return mode->hdisplay > max_src_w || mode->vdisplay > max_src_h;
> +}
> +

I don't really like this. If we do something like this
then it should be the scaler code that checks this stuff.

However, after pondering about this more I'm actually
leaning towards using 4:4:4 output whenever possible,
only going for 4:2:0 if absolutely necessary. That
avoids having to deal with all the annoying scaler/etc
limitations.

>  static enum intel_output_format
>  intel_dp_output_format(struct intel_connector *connector,
> +		       const struct drm_display_mode *mode,
>  		       enum intel_output_format sink_format)
>  {
>  	struct intel_dp *intel_dp = intel_attached_dp(connector);
> +	struct drm_i915_private *i915 = to_i915(connector->base.dev);
>  
>  	if (!connector->base.ycbcr_420_allowed ||
>  	    sink_format != INTEL_OUTPUT_FORMAT_YCBCR420)
> @@ -820,8 +845,15 @@ intel_dp_output_format(struct intel_connector *connector,
>  
>  	if (intel_dp->dfp.ycbcr_444_to_420)
>  		return INTEL_OUTPUT_FORMAT_YCBCR444;
> -	else
> +
> +	/*
> +	 * For YCbCr420 output, scaler is required for downsampling
> +	 * So go for native YCbCr420 only if there are no scaler constraints.
> +	 */
> +	if (!ycbcr420_scaler_constraints(i915, mode))
>  		return INTEL_OUTPUT_FORMAT_YCBCR420;
> +
> +	return INTEL_OUTPUT_FORMAT_RGB;
>  }
>  
>  int intel_dp_min_bpp(enum intel_output_format output_format)
> @@ -857,7 +889,7 @@ intel_dp_mode_min_output_bpp(struct intel_connector *connector,
>  	else
>  		sink_format = INTEL_OUTPUT_FORMAT_RGB;
>  
> -	output_format = intel_dp_output_format(connector, sink_format);
> +	output_format = intel_dp_output_format(connector, mode, sink_format);
>  
>  	return intel_dp_output_bpp(output_format, intel_dp_min_bpp(output_format));
>  }
> @@ -2052,7 +2084,8 @@ intel_dp_compute_output_format(struct intel_encoder *encoder,
>  		crtc_state->sink_format = INTEL_OUTPUT_FORMAT_RGB;
>  	}
>  
> -	crtc_state->output_format = intel_dp_output_format(connector, crtc_state->sink_format);
> +	crtc_state->output_format = intel_dp_output_format(connector, adjusted_mode,
> +							   crtc_state->sink_format);
>  
>  	ret = intel_dp_compute_link_config(encoder, crtc_state, conn_state,
>  					   respect_downstream_limits);
> @@ -2063,7 +2096,7 @@ intel_dp_compute_output_format(struct intel_encoder *encoder,
>  			return ret;
>  
>  		crtc_state->sink_format = INTEL_OUTPUT_FORMAT_YCBCR420;
> -		crtc_state->output_format = intel_dp_output_format(connector,
> +		crtc_state->output_format = intel_dp_output_format(connector, adjusted_mode,
>  								   crtc_state->sink_format);
>  		ret = intel_dp_compute_link_config(encoder, crtc_state, conn_state,
>  						   respect_downstream_limits);
> -- 
> 2.25.1

-- 
Ville Syrjälä
Intel