drm/dp: add an API to indicate if sink supports VSC SDP

YUV420 format is supported only in the VSC SDP packet and not through
MSA. Hence add an API which indicates the sink support which can be used
by the rest of the DP programming.

changes in v5:
	- rebased on top of drm-tip

changes in v4:
	- bail out early if dpcd rev check fails

changes in v3:
	- fix the commit title prefix to drm/dp
	- get rid of redundant !!
	- break out this change from series [1] to get acks from drm core
	  maintainers

Changes in v2:
	- Move VSC SDP support check API from dp_panel.c to
	  drm_dp_helper.c

[1]: https://patchwork.freedesktop.org/series/129180/Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Paloma Arellano <quic_parellan@quicinc.com>
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240215191556.3227259-1-quic_abhinavk@quicinc.com

drivers/gpu/drm/display/drm_dp_helper.c

@@ -2913,6 +2913,29 @@ void drm_dp_vsc_sdp_log(struct drm_printer *p, const struct drm_dp_vsc_sdp *vsc)
 }
 EXPORT_SYMBOL(drm_dp_vsc_sdp_log);
 
+/**
+ * drm_dp_vsc_sdp_supported() - check if vsc sdp is supported
+ * @aux: DisplayPort AUX channel
+ * @dpcd: DisplayPort configuration data
+ *
+ * Returns true if vsc sdp is supported, else returns false
+ */
+bool drm_dp_vsc_sdp_supported(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	u8 rx_feature;
+
+	if (dpcd[DP_DPCD_REV] < DP_DPCD_REV_13)
+		return false;
+
+	if (drm_dp_dpcd_readb(aux, DP_DPRX_FEATURE_ENUMERATION_LIST, &rx_feature) != 1) {
+		drm_dbg_dp(aux->drm_dev, "failed to read DP_DPRX_FEATURE_ENUMERATION_LIST\n");
+		return false;
+	}
+
+	return (rx_feature & DP_VSC_SDP_EXT_FOR_COLORIMETRY_SUPPORTED);
+}
+EXPORT_SYMBOL(drm_dp_vsc_sdp_supported);
+
 /**
  * drm_dp_vsc_sdp_pack() - pack a given vsc sdp into generic dp_sdp
  * @vsc: vsc sdp initialized according to its purpose as defined in

include/drm/display/drm_dp_helper.h

@@ -100,6 +100,8 @@ struct drm_dp_vsc_sdp {
 
 void drm_dp_vsc_sdp_log(struct drm_printer *p, const struct drm_dp_vsc_sdp *vsc);
 
+bool drm_dp_vsc_sdp_supported(struct drm_dp_aux *aux, const u8 dpcd[DP_RECEIVER_CAP_SIZE]);
+
 int drm_dp_psr_setup_time(const u8 psr_cap[EDP_PSR_RECEIVER_CAP_SIZE]);
 
 static inline int