Re: [PATCH 2/2] drm/i915/dp: set VSC_SDP MSA delegation only for capable sinks

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

On Thu, 09 Jul 2026, Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com> wrote:
> Per DP 1.4a section 2.2.4.3, the MSA MISC1 VSC_SDP bit signals that
> the sink should defer colorimetry to the VSC SDP. It should only be set
> when the sink advertises DP_VSC_SDP_EXT_FOR_COLORIMETRY_SUPPORTED and a
> VSC SDP with pixel encoding/colorimetry payload will actually be sent.
>
> Fold the colorimetry_support check into intel_dp_needs_vsc_colorimetry()
> so both intel_ddi_set_dp_msa() and intel_dp_compute_vsc_sdp() share a
> single consistent gate.
>
> Assisted-by: GitHub_Copilot:claude-sonnet-4.6

Who would teach Claude to add proper Fixes: and Cc: stable tags so
important fixes actually propagate to users in a timely fashion?

BR,
Jani.

> Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_ddi.c |  2 ++
>  drivers/gpu/drm/i915/display/intel_dp.c  | 14 ++++++++++----
>  2 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> index c764472bd69a..13010375e21b 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> @@ -469,6 +469,8 @@ void intel_ddi_set_dp_msa(const struct intel_crtc_state *crtc_state,
>  	 * of Color Encoding Format and Content Color Gamut] while sending
>  	 * YCBCR 420, HDR BT.2020 signals we should program MSA MISC1 fields
>  	 * which indicate VSC SDP for the Pixel Encoding/Colorimetry Format.
> +	 * Only set the delegation bit when the content needs it and
> +	 * the sink advertises support.
>  	 */
>  	if (intel_dp_needs_vsc_colorimetry(crtc_state, conn_state))
>  		temp |= DP_MSA_MISC_COLOR_VSC_SDP;
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 93282694c29b..53688c5bef74 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -3163,8 +3163,7 @@ static void intel_dp_compute_vsc_sdp(struct intel_dp *intel_dp,
>  {
>  	struct drm_dp_vsc_sdp *vsc;
>  
> -	if ((!intel_dp->colorimetry_support ||
> -	     !intel_dp_needs_vsc_colorimetry(crtc_state, conn_state)) &&
> +	if (!intel_dp_needs_vsc_colorimetry(crtc_state, conn_state) &&
>  	    !crtc_state->has_psr)
>  		return;
>  
> @@ -3173,7 +3172,6 @@ static void intel_dp_compute_vsc_sdp(struct intel_dp *intel_dp,
>  	crtc_state->infoframes.enable |= intel_hdmi_infoframe_enable(DP_SDP_VSC);
>  	vsc->sdp_type = DP_SDP_VSC;
>  
> -	/* Needs colorimetry */
>  	if (intel_dp_needs_vsc_colorimetry(crtc_state, conn_state)) {
>  		intel_dp_compute_vsc_colorimetry(crtc_state, conn_state,
>  						 vsc);
> @@ -5103,11 +5101,19 @@ bool
>  intel_dp_needs_vsc_colorimetry(const struct intel_crtc_state *crtc_state,
>  			       const struct drm_connector_state *conn_state)
>  {
> +	struct intel_dp *intel_dp =
> +		enc_to_intel_dp(to_intel_encoder(conn_state->best_encoder));
> +
>  	/*
>  	 * As per DP 1.4a spec section 2.2.4.3 [MSA Field for Indication
>  	 * of Color Encoding Format and Content Color Gamut], in order to
> -	 * sending YCBCR 420 or HDR BT.2020 signals we should use DP VSC SDP.
> +	 * send YCBCR 420 or HDR BT.2020 signals we should use DP VSC SDP.
> +	 * Only signal this when the sink advertises VSC SDP colorimetry
> +	 * support.
>  	 */
> +	if (!intel_dp->colorimetry_support)
> +		return false;
> +
>  	if (crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420)
>  		return true;

-- 
Jani Nikula, Intel