Re: [PATCH] drm/i915/xe3lpd: Prune modes for YUV420

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

On Mon, Jun 09, 2025 at 10:15:48PM +0530, Suraj Kandpal wrote:
> We only support resolution up to 4k for single pipe when using
> YUV420 format so we prune these modes and restrict the plane size
> at src. This is because pipe scaling will not support YUV420 scaling
> for hwidth > 4096.
> 
> --v2
> -Use output format to check [Ville]
> -Add Bspec references
> -Modify commit messge to point to why this is needed
> 
> Bspec: 49247, 50441
> Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index d04609460e8c..2691eeb50a26 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1419,6 +1419,7 @@ intel_dp_mode_valid(struct drm_connector *_connector,
>  	struct intel_display *display = to_intel_display(_connector->dev);
>  	struct intel_connector *connector = to_intel_connector(_connector);
>  	struct intel_dp *intel_dp = intel_attached_dp(connector);
> +	enum intel_output_format sink_format, output_format;
>  	const struct drm_display_mode *fixed_mode;
>  	int target_clock = mode->clock;
>  	int max_rate, mode_rate, max_lanes, max_link_clock;
> @@ -1452,6 +1453,14 @@ intel_dp_mode_valid(struct drm_connector *_connector,
>  						     mode->hdisplay, target_clock);
>  	max_dotclk *= num_joined_pipes;
>  
> +	sink_format = intel_dp_sink_format(connector, mode);
> +	output_format = intel_dp_output_format(connector, sink_format);
> +	if (num_joined_pipes == 1) {
> +		if (output_format == INTEL_OUTPUT_FORMAT_YCBCR420 &&
> +		    mode->hdisplay > 4096)

Sprinkling random hw limits all over the codebase isn't a very good
approach. I think we want some kind of skl_scaler_mode_valid() for this.
And that should probably be routed via a intel_pfit_mode_valid() to keep
the level of abstraction similar to intel_pfit_compute_config().

> +			return MODE_NO_420;
> +	}
> +
>  	if (target_clock > max_dotclk)
>  		return MODE_CLOCK_HIGH;
>  
> @@ -1467,11 +1476,8 @@ intel_dp_mode_valid(struct drm_connector *_connector,
>  					   intel_dp_mode_min_output_bpp(connector, mode));
>  
>  	if (intel_dp_has_dsc(connector)) {
> -		enum intel_output_format sink_format, output_format;
>  		int pipe_bpp;
>  
> -		sink_format = intel_dp_sink_format(connector, mode);
> -		output_format = intel_dp_output_format(connector, sink_format);
>  		/*
>  		 * TBD pass the connector BPC,
>  		 * for now U8_MAX so that max BPC on that platform would be picked
> -- 
> 2.34.1

-- 
Ville Syrjälä
Intel