[PATCH 2/2] drm/i915/dp: Add checking of YCBCR420 Pass-through to YCBCR420 outputs.

[Gwan-gyeong Mun]

When a DP downstream uses a DP to HDMI active converter, the active
converter needs to support YCbCr420 Pass-through to enable DP YCbCr 4:2:0
outputs.

Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 26 +++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index f4dede6253f8..824ed8096426 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -2298,6 +2298,22 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 	return 0;
 }
 
+static bool
+intel_dp_downstream_is_hdmi_detailed_cap_info(struct intel_dp *intel_dp)
+{
+	int type = intel_dp->downstream_ports[0] & DP_DS_PORT_TYPE_MASK;
+	bool detailed_cap_info = intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] &
+				 DP_DETAILED_CAP_INFO_AVAILABLE;
+
+	return type == DP_DS_PORT_TYPE_HDMI && detailed_cap_info;
+}
+
+static bool
+intel_dp_downstream_supports_ycbcr_420_passthru(struct intel_dp *intel_dp)
+{
+	return intel_dp->downstream_ports[3] & DP_DS_YCBCR420_PASSTHRU_SUPPORT;
+}
+
 static int
 intel_dp_ycbcr420_config(struct intel_dp *intel_dp,
 			 struct drm_connector *connector,
@@ -2314,6 +2330,16 @@ intel_dp_ycbcr420_config(struct intel_dp *intel_dp,
 	    !connector->ycbcr_420_allowed)
 		return 0;
 
+	/*
+	 * When a DP downstream uses a DP to HDMI active converter,
+	 * the active converter needs to support YCbCr420 Pass-through.
+	 */
+	if (drm_dp_is_branch(intel_dp->dpcd)) {
+		if (intel_dp_downstream_is_hdmi_detailed_cap_info(intel_dp) &&
+		    !intel_dp_downstream_supports_ycbcr_420_passthru(intel_dp))
+			return 0;
+	}
+
 	crtc_state->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;
 
 	/* YCBCR 420 output conversion needs a scaler */
-- 
2.24.1