drm: bridge: dw_hdmi: Enable GCP only for Deep Color

HDMI1.4b specification section 6.5.3:
Source shall only send GCPs with non-zero CD to sinks
that indicate support for Deep Color.

DW HDMI GCP default enabled, but only transmit CD
and do not handle AVMUTE, PP norDefault_Phase (yet).
Disable Auto GCP when 24-bit color for sinks that not support Deep Color.

Signed-off-by: Sandor Yu <Sandor.yu@nxp.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/78fa41e4fb3d3d53354034bc221fcf870dbac617.1649989179.git.Sandor.yu@nxp.com

drivers/gpu/drm/bridge/synopsys/dw-hdmi.c

@@ -1108,6 +1108,8 @@ static void hdmi_video_packetize(struct dw_hdmi *hdmi)
 	unsigned int output_select = HDMI_VP_CONF_OUTPUT_SELECTOR_PP;
 	struct hdmi_data_info *hdmi_data = &hdmi->hdmi_data;
 	u8 val, vp_conf;
+	u8 clear_gcp_auto = 0;
+
 
 	if (hdmi_bus_fmt_is_rgb(hdmi->hdmi_data.enc_out_bus_format) ||
 	    hdmi_bus_fmt_is_yuv444(hdmi->hdmi_data.enc_out_bus_format) ||
@@ -1117,6 +1119,7 @@ static void hdmi_video_packetize(struct dw_hdmi *hdmi)
 		case 8:
 			color_depth = 4;
 			output_select = HDMI_VP_CONF_OUTPUT_SELECTOR_BYPASS;
+			clear_gcp_auto = 1;
 			break;
 		case 10:
 			color_depth = 5;
@@ -1136,6 +1139,7 @@ static void hdmi_video_packetize(struct dw_hdmi *hdmi)
 		case 0:
 		case 8:
 			remap_size = HDMI_VP_REMAP_YCC422_16bit;
+			clear_gcp_auto = 1;
 			break;
 		case 10:
 			remap_size = HDMI_VP_REMAP_YCC422_20bit;
@@ -1160,6 +1164,19 @@ static void hdmi_video_packetize(struct dw_hdmi *hdmi)
 		HDMI_VP_PR_CD_DESIRED_PR_FACTOR_MASK);
 	hdmi_writeb(hdmi, val, HDMI_VP_PR_CD);
 
+	/* HDMI1.4b specification section 6.5.3:
+	 * Source shall only send GCPs with non-zero CD to sinks
+	 * that indicate support for Deep Color.
+	 * GCP only transmit CD and do not handle AVMUTE, PP norDefault_Phase (yet).
+	 * Disable Auto GCP when 24-bit color for sinks that not support Deep Color.
+	 */
+	val = hdmi_readb(hdmi, HDMI_FC_DATAUTO3);
+	if (clear_gcp_auto == 1)
+		val &= ~HDMI_FC_DATAUTO3_GCP_AUTO;
+	else
+		val |= HDMI_FC_DATAUTO3_GCP_AUTO;
+	hdmi_writeb(hdmi, val, HDMI_FC_DATAUTO3);
+
 	hdmi_modb(hdmi, HDMI_VP_STUFF_PR_STUFFING_STUFFING_MODE,
 		  HDMI_VP_STUFF_PR_STUFFING_MASK, HDMI_VP_STUFF);
 

drivers/gpu/drm/bridge/synopsys/dw-hdmi.h

@@ -850,6 +850,9 @@ enum {
 	HDMI_FC_DATAUTO0_VSD_MASK = 0x08,
 	HDMI_FC_DATAUTO0_VSD_OFFSET = 3,
 
+/* FC_DATAUTO3 field values */
+	HDMI_FC_DATAUTO3_GCP_AUTO = 0x04,
+
 /* PHY_CONF0 field values */
 	HDMI_PHY_CONF0_PDZ_MASK = 0x80,
 	HDMI_PHY_CONF0_PDZ_OFFSET = 7,