Re: [PATCH v2 4/9] drm/i915/dp: Restructure the sink/output format selection

["Nautiyal, Ankit K" <ankit.k.nautiyal@intel.com>]

On 4/9/2026 3:45 PM, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Restructure intel_dp_compute_output_format() to resemble the new
> intel_hdmi_compute_output_formats().
>
> Again, we basically have two main code paths:
> - YCbCr 4:2:0 only modes
> - everything else including YCbCr 4:2:0 also modes
>
> Take the exact same approach with the DP code, making the
> format selection much less convoluted.
>
> Cc: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>


> ---
>   drivers/gpu/drm/i915/display/intel_dp.c | 98 +++++++++++++++++--------
>   1 file changed, 69 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index b8b6d62fb275..ed5841f224ee 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1379,6 +1379,28 @@ intel_dp_mode_valid_downstream(struct intel_connector *connector,
>   	return MODE_OK;
>   }
>   
> +static enum drm_mode_status
> +intel_dp_sink_format_valid(struct intel_connector *connector,
> +			   const struct drm_display_mode *mode,
> +			   enum intel_output_format sink_format)
> +{
> +	const struct drm_display_info *info = &connector->base.display_info;
> +
> +	switch (sink_format) {
> +	case INTEL_OUTPUT_FORMAT_YCBCR420:
> +		if (!connector->base.ycbcr_420_allowed ||
> +		    !drm_mode_is_420(info, mode))
> +			return MODE_NO_420;
> +
> +		return MODE_OK;
> +	case INTEL_OUTPUT_FORMAT_RGB:
> +		return MODE_OK;
> +	default:
> +		MISSING_CASE(sink_format);
> +		return MODE_BAD;
> +	}
> +}
> +
>   int intel_dp_max_hdisplay_per_pipe(struct intel_display *display)
>   {
>   	return DISPLAY_VER(display) >= 30 ? 6144 : 5120;
> @@ -3338,41 +3360,59 @@ static int
>   intel_dp_compute_output_format(struct intel_encoder *encoder,
>   			       struct intel_crtc_state *crtc_state,
>   			       struct drm_connector_state *conn_state,
> -			       bool respect_downstream_limits)
> +			       bool respect_downstream_limits,
> +			       enum intel_output_format sink_format)
>   {
> -	struct intel_display *display = to_intel_display(encoder);
>   	struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
>   	struct intel_connector *connector = intel_dp->attached_connector;
> -	const struct drm_display_info *info = &connector->base.display_info;
>   	const struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
> -	bool ycbcr_420_only;
> -	int ret;
>   
> -	ycbcr_420_only = drm_mode_is_420_only(info, adjusted_mode);
> -
> -	if (ycbcr_420_only && !connector->base.ycbcr_420_allowed) {
> -		drm_dbg_kms(display->drm,
> -			    "YCbCr 4:2:0 mode but YCbCr 4:2:0 output not possible. Falling back to RGB.\n");
> -		crtc_state->sink_format = INTEL_OUTPUT_FORMAT_RGB;
> -	} else {
> -		crtc_state->sink_format = intel_dp_sink_format(connector, adjusted_mode);
> -	}
> +	if (intel_dp_sink_format_valid(connector, adjusted_mode,
> +				       sink_format) != MODE_OK)
> +		return -EINVAL;
>   
> +	crtc_state->sink_format = sink_format;
>   	crtc_state->output_format = intel_dp_output_format(connector, crtc_state->sink_format);
>   
> -	ret = intel_dp_compute_link_config(encoder, crtc_state, conn_state,
> -					   respect_downstream_limits);
> -	if (ret) {
> -		if (crtc_state->sink_format == INTEL_OUTPUT_FORMAT_YCBCR420 ||
> -		    !connector->base.ycbcr_420_allowed ||
> -		    !drm_mode_is_420_also(info, adjusted_mode))
> -			return ret;
> -
> -		crtc_state->sink_format = INTEL_OUTPUT_FORMAT_YCBCR420;
> -		crtc_state->output_format = intel_dp_output_format(connector,
> -								   crtc_state->sink_format);
> -		ret = intel_dp_compute_link_config(encoder, crtc_state, conn_state,
> -						   respect_downstream_limits);
> +	return intel_dp_compute_link_config(encoder, crtc_state, conn_state,
> +					    respect_downstream_limits);
> +}
> +
> +static int
> +intel_dp_compute_formats(struct intel_encoder *encoder,
> +			 struct intel_crtc_state *crtc_state,
> +			 struct drm_connector_state *conn_state,
> +			 bool respect_downstream_limits)
> +{
> +	struct intel_display *display = to_intel_display(encoder);
> +	struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
> +	struct intel_connector *connector = intel_dp->attached_connector;
> +	const struct drm_display_info *info = &connector->base.display_info;
> +	const struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
> +	int ret;
> +
> +	if (drm_mode_is_420_only(info, adjusted_mode)) {
> +		ret = intel_dp_compute_output_format(encoder, crtc_state, conn_state,
> +						     respect_downstream_limits,
> +						     INTEL_OUTPUT_FORMAT_YCBCR420);
> +
> +		if (ret) {
> +			drm_dbg_kms(display->drm,
> +				    "YCbCr 4:2:0 mode but YCbCr 4:2:0 output not possible. Falling back to RGB.\n");
> +
> +			ret = intel_dp_compute_output_format(encoder, crtc_state, conn_state,
> +							     respect_downstream_limits,
> +							     INTEL_OUTPUT_FORMAT_RGB);
> +		}
> +	} else {
> +		ret = intel_dp_compute_output_format(encoder, crtc_state, conn_state,
> +						     respect_downstream_limits,
> +						     INTEL_OUTPUT_FORMAT_RGB);
> +
> +		if (ret && drm_mode_is_420_also(info, adjusted_mode))
> +			ret = intel_dp_compute_output_format(encoder, crtc_state, conn_state,
> +							     respect_downstream_limits,
> +							     INTEL_OUTPUT_FORMAT_YCBCR420);
>   	}
>   
>   	return ret;
> @@ -3547,9 +3587,9 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>   	 * Try to respect downstream TMDS clock limits first, if
>   	 * that fails assume the user might know something we don't.
>   	 */
> -	ret = intel_dp_compute_output_format(encoder, pipe_config, conn_state, true);
> +	ret = intel_dp_compute_formats(encoder, pipe_config, conn_state, true);
>   	if (ret)
> -		ret = intel_dp_compute_output_format(encoder, pipe_config, conn_state, false);
> +		ret = intel_dp_compute_formats(encoder, pipe_config, conn_state, false);
>   	if (ret)
>   		return ret;
>