Re: [PATCH v13 13/27] drm/i915: Implement the "color format" DRM property

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

On Mon, Apr 13, 2026 at 12:07:27PM +0200, Nicolas Frattaroli wrote:
> Implement the "color format" DRM property for both DP and HDMI.  The
> values of the property include RGB, YCbCr420, YCbCr444 and Auto. Auto
> will pick RGB, with a fallback to YCbCr420.
> 
> The mask of supported formats by the source exposed by the property is
> an optimistic scenario, as specific DFP-related caveats can't be
> established before an EDID is present.
> 
> Should the explicitly requested color format not be supported by the
> sink (or by the source in combination with the sink), then an error is
> returned to userspace, so that it can make a better choice.
> 
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> ---
>  drivers/gpu/drm/i915/display/intel_connector.c | 10 +++++++
>  drivers/gpu/drm/i915/display/intel_connector.h |  1 +
>  drivers/gpu/drm/i915/display/intel_dp.c        | 38 +++++++++++++++++++++++---
>  drivers/gpu/drm/i915/display/intel_hdmi.c      | 38 +++++++++++++++++++++++---
>  4 files changed, 79 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_connector.c b/drivers/gpu/drm/i915/display/intel_connector.c
> index 7ef9338d67ab..b1a21dd77af6 100644
> --- a/drivers/gpu/drm/i915/display/intel_connector.c
> +++ b/drivers/gpu/drm/i915/display/intel_connector.c
> @@ -338,3 +338,13 @@ intel_attach_scaling_mode_property(struct drm_connector *connector)
>  
>  	connector->state->scaling_mode = DRM_MODE_SCALE_ASPECT;
>  }
> +
> +void
> +intel_attach_color_format_property(struct drm_connector *connector)
> +{
> +	const unsigned long fmts = BIT(DRM_OUTPUT_COLOR_FORMAT_RGB444) |
> +				   BIT(DRM_OUTPUT_COLOR_FORMAT_YCBCR444) |
> +				   BIT(DRM_OUTPUT_COLOR_FORMAT_YCBCR420);

We're going to need different formats for different platforms, and 
for DP vs. HDMI.

For HDMI it should be fairly simple if we have the
ycbcr420_allowed and ycbcr444_allowed things to consult.

For DP I'm not sure if we want to advertise YCbCr output support
for platforms that can't produce it without help from the PCON.
If we know there is an on board PCON that can do it, then the answer
is probably yes. But without that it might be best to not advertise
the relevant formats unless source_can_output() tells us that it can
be directly output. We could at least start with that, and revisit
it later if some situations arise where eg. having explicit 4:2:0
output on older platforms is beneficial.

I think you want to split this to separate DP vs. HDMI patches since
the two require quite different logic.

> +
> +	drm_connector_attach_color_format_property(connector, fmts);
> +}
> diff --git a/drivers/gpu/drm/i915/display/intel_connector.h b/drivers/gpu/drm/i915/display/intel_connector.h
> index 0aa86626e646..c77b7aac02cb 100644
> --- a/drivers/gpu/drm/i915/display/intel_connector.h
> +++ b/drivers/gpu/drm/i915/display/intel_connector.h
> @@ -34,5 +34,6 @@ void intel_attach_dp_colorspace_property(struct drm_connector *connector);
>  void intel_attach_scaling_mode_property(struct drm_connector *connector);
>  void intel_connector_queue_modeset_retry_work(struct intel_connector *connector);
>  void intel_connector_cancel_modeset_retry_work(struct intel_connector *connector);
> +void intel_attach_color_format_property(struct drm_connector *connector);
>  
>  #endif /* __INTEL_CONNECTOR_H__ */
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 47bd3d59ea93..3b2293415b55 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -3398,10 +3398,10 @@ intel_dp_compute_output_format(struct intel_encoder *encoder,
>  }
>  
>  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)
> +intel_dp_compute_formats_auto(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);
> @@ -3437,6 +3437,34 @@ intel_dp_compute_formats(struct intel_encoder *encoder,
>  	return ret;
>  }
>  
> +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)
> +{
> +	switch (conn_state->color_format) {
> +	case DRM_CONNECTOR_COLOR_FORMAT_RGB444:
> +		return intel_dp_compute_output_format(encoder, crtc_state, conn_state,
> +						      respect_downstream_limits,
> +						      INTEL_OUTPUT_FORMAT_RGB);
> +	case DRM_CONNECTOR_COLOR_FORMAT_YCBCR444:
> +		return intel_dp_compute_output_format(encoder, crtc_state, conn_state,
> +						      respect_downstream_limits,
> +						      INTEL_OUTPUT_FORMAT_YCBCR444);
> +	case DRM_CONNECTOR_COLOR_FORMAT_YCBCR420:
> +		return intel_dp_compute_output_format(encoder, crtc_state, conn_state,
> +						      respect_downstream_limits,
> +						      INTEL_OUTPUT_FORMAT_YCBCR420);
> +	case DRM_CONNECTOR_COLOR_FORMAT_AUTO:
> +		return intel_dp_compute_formats_auto(encoder, crtc_state, conn_state,
> +						     respect_downstream_limits);
> +	default:
> +		MISSING_CASE(conn_state->color_format);
> +		return -EINVAL;
> +	}
> +}
> +
>  void
>  intel_dp_audio_compute_config(struct intel_encoder *encoder,
>  			      struct intel_crtc_state *pipe_config,
> @@ -7025,6 +7053,8 @@ intel_dp_add_properties(struct intel_dp *intel_dp, struct drm_connector *_connec
>  
>  	if (HAS_VRR(display))
>  		drm_connector_attach_vrr_capable_property(&connector->base);
> +
> +	intel_attach_color_format_property(&connector->base);
>  }
>  
>  static void
> diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
> index 5ab5b5f85cde..632498e3702b 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdmi.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
> @@ -2307,10 +2307,10 @@ static int intel_hdmi_compute_output_format(struct intel_encoder *encoder,
>  	return intel_hdmi_compute_clock(encoder, crtc_state, respect_downstream_limits);
>  }
>  
> -static int intel_hdmi_compute_formats(struct intel_encoder *encoder,
> -				      struct intel_crtc_state *crtc_state,
> -				      const struct drm_connector_state *conn_state,
> -				      bool respect_downstream_limits)
> +static int intel_hdmi_compute_formats_auto(struct intel_encoder *encoder,
> +					   struct intel_crtc_state *crtc_state,
> +					   const struct drm_connector_state *conn_state,
> +					   bool respect_downstream_limits)
>  {
>  	struct intel_display *display = to_intel_display(encoder);
>  	struct intel_connector *connector = to_intel_connector(conn_state->connector);
> @@ -2345,6 +2345,35 @@ static int intel_hdmi_compute_formats(struct intel_encoder *encoder,
>  	return ret;
>  }
>  
> +static int intel_hdmi_compute_formats(struct intel_encoder *encoder,
> +				      struct intel_crtc_state *crtc_state,
> +				      const struct drm_connector_state *conn_state,
> +				      bool respect_downstream_limits)
> +{
> +	struct intel_connector *connector = to_intel_connector(conn_state->connector);
> +
> +	switch (conn_state->color_format) {
> +	case DRM_CONNECTOR_COLOR_FORMAT_RGB444:
> +		return intel_hdmi_compute_output_format(encoder, crtc_state, connector,
> +							respect_downstream_limits,
> +							INTEL_OUTPUT_FORMAT_RGB);
> +	case DRM_CONNECTOR_COLOR_FORMAT_YCBCR444:
> +		return intel_hdmi_compute_output_format(encoder, crtc_state, connector,
> +							respect_downstream_limits,
> +							INTEL_OUTPUT_FORMAT_YCBCR444);
> +	case DRM_CONNECTOR_COLOR_FORMAT_YCBCR420:
> +		return intel_hdmi_compute_output_format(encoder, crtc_state, connector,
> +							respect_downstream_limits,
> +							INTEL_OUTPUT_FORMAT_YCBCR420);
> +	case DRM_CONNECTOR_COLOR_FORMAT_AUTO:
> +		return intel_hdmi_compute_formats_auto(encoder, crtc_state, conn_state,
> +						       respect_downstream_limits);
> +	default:
> +		MISSING_CASE(conn_state->color_format);
> +		return -EINVAL;
> +	}
> +}
> +
>  static bool intel_hdmi_is_cloned(const struct intel_crtc_state *crtc_state)
>  {
>  	return crtc_state->uapi.encoder_mask &&
> @@ -2729,6 +2758,7 @@ intel_hdmi_add_properties(struct intel_hdmi *intel_hdmi, struct drm_connector *_
>  
>  	intel_attach_hdmi_colorspace_property(&connector->base);
>  	drm_connector_attach_content_type_property(&connector->base);
> +	intel_attach_color_format_property(&connector->base);
>  
>  	if (DISPLAY_VER(display) >= 10)
>  		drm_connector_attach_hdr_output_metadata_property(&connector->base);
> 
> -- 
> 2.53.0

-- 
Ville Syrjälä
Intel

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