backend/drm: unconditionally set "content type" to graphics

CTA-861-G says that "graphics" is used to indicate non-analog (ie,
digital) content. With that bit set, the sink should turn off analog
reconstruction and other related filtering.

backend/drm/atomic.c

@@ -280,6 +280,10 @@ static bool atomic_crtc_commit(struct wlr_drm_connector *conn,
 		atomic_add(&atom, conn->id, conn->props.link_status,
 			DRM_MODE_LINK_STATUS_GOOD);
 	}
+	if (active && conn->props.content_type != 0) {
+		atomic_add(&atom, conn->id, conn->props.content_type,
+			DRM_MODE_CONTENT_TYPE_GRAPHICS);
+	}
 	atomic_add(&atom, crtc->id, crtc->props.mode_id, mode_id);
 	atomic_add(&atom, crtc->id, crtc->props.active, active);
 	if (active) {

backend/drm/properties.c

@@ -24,6 +24,7 @@ static const struct prop_info connector_info[] = {
 	{ "DPMS", INDEX(dpms) },
 	{ "EDID", INDEX(edid) },
 	{ "PATH", INDEX(path) },
+	{ "content type", INDEX(content_type) },
 	{ "link-status", INDEX(link_status) },
 	{ "non-desktop", INDEX(non_desktop) },
 	{ "panel orientation", INDEX(panel_orientation) },

include/backend/drm/properties.h

@@ -20,6 +20,7 @@ union wlr_drm_connector_props {
 		uint32_t subconnector; // not guaranteed to exist
 		uint32_t non_desktop;
 		uint32_t panel_orientation; // not guaranteed to exist
+		uint32_t content_type; // not guaranteed to exist
 
 		// atomic-modesetting only