drm/vc4: hdmi: Use gcp=4 for YCC422

HDMI 1.4 6.2.4

YCC4:2:2 is also 36-bit mode but does not require
the further use of the Deep Color modes
described in section 6.5.2 and 6.5.3 (GCP sections)

So we don't want to signal bpc here

Author: popcornmix

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -1002,6 +1002,8 @@ static void vc5_hdmi_set_timings(struct vc4_hdmi *vc4_hdmi,
 				 struct drm_connector_state *state,
 				 struct drm_display_mode *mode)
 {
+	struct vc4_hdmi_connector_state *vc4_state =
+		conn_state_to_vc4_hdmi_conn_state(state);
 	bool hsync_pos = mode->flags & DRM_MODE_FLAG_PHSYNC;
 	bool vsync_pos = mode->flags & DRM_MODE_FLAG_PVSYNC;
 	bool interlaced = mode->flags & DRM_MODE_FLAG_INTERLACE;
@@ -1065,6 +1067,12 @@ static void vc5_hdmi_set_timings(struct vc4_hdmi *vc4_hdmi,
 		break;
 	}
 
+	// YCC422 is always 36-bit and not considered deep colour so doesn't signal in GCP
+	if (vc4_state->output_format == DRM_COLOR_FORMAT_YCRCB422) {
+		gcp = 4;
+		gcp_en = false;
+	}
+
 	reg = HDMI_READ(HDMI_DEEP_COLOR_CONFIG_1);
 	reg &= ~(VC5_HDMI_DEEP_COLOR_CONFIG_1_INIT_PACK_PHASE_MASK |
 		 VC5_HDMI_DEEP_COLOR_CONFIG_1_COLOR_DEPTH_MASK);