backend/drm: add support for the link-status property

backend/drm/atomic.c

@@ -104,7 +104,8 @@ static bool atomic_crtc_pageflip(struct wlr_drm_backend *drm,
 			drmModeDestroyPropertyBlob(drm->fd, crtc->mode_id);
 		}
 
-		if (drmModeCreatePropertyBlob(drm->fd, mode, sizeof(*mode), &crtc->mode_id)) {
+		if (drmModeCreatePropertyBlob(drm->fd, mode, sizeof(*mode),
+				&crtc->mode_id)) {
 			wlr_log_errno(WLR_ERROR, "Unable to create property blob");
 			return false;
 		}
@@ -120,6 +121,10 @@ static bool atomic_crtc_pageflip(struct wlr_drm_backend *drm,
 	struct atomic atom;
 	atomic_begin(crtc, &atom);
 	atomic_add(&atom, conn->id, conn->props.crtc_id, crtc->id);
+	if (mode != NULL && conn->props.link_status != 0) {
+		atomic_add(&atom, conn->id, conn->props.link_status,
+			DRM_MODE_LINK_STATUS_GOOD);
+	}
 	atomic_add(&atom, crtc->id, crtc->props.mode_id, crtc->mode_id);
 	atomic_add(&atom, crtc->id, crtc->props.active, 1);
 	set_plane_props(&atom, crtc->primary, crtc->id, fb_id, true);

backend/drm/drm.c

@@ -1034,6 +1034,24 @@ void scan_drm_connectors(struct wlr_drm_backend *drm) {
 			wlr_conn->crtc = NULL;
 		}
 
+		// This can only happen *after* hotplug, since we haven't read the
+		// connector properties yet
+		if (wlr_conn->props.link_status != 0) {
+			uint64_t link_status;
+			if (!get_drm_prop(drm->fd, wlr_conn->id,
+					wlr_conn->props.link_status, &link_status)) {
+				wlr_log(WLR_ERROR, "Failed to get link status for '%s'",
+					wlr_conn->output.name);
+				continue;
+			}
+
+			if (link_status == DRM_MODE_LINK_STATUS_BAD) {
+				// We need to reload our list of modes and force a modeset
+				wlr_log(WLR_INFO, "Bad link for '%s'", wlr_conn->output.name);
+				drm_connector_cleanup(wlr_conn);
+			}
+		}
+
 		if (wlr_conn->state == WLR_DRM_CONN_DISCONNECTED &&
 				drm_conn->connection == DRM_MODE_CONNECTED) {
 			wlr_log(WLR_INFO, "'%s' connected", wlr_conn->output.name);

backend/drm/properties.c

@@ -22,6 +22,7 @@ static const struct prop_info connector_info[] = {
 	{ "CRTC_ID",     INDEX(crtc_id) },
 	{ "DPMS",        INDEX(dpms) },
 	{ "EDID",        INDEX(edid) },
+	{ "link-status", INDEX(link_status) },
 #undef INDEX
 };
 
@@ -87,7 +88,8 @@ static bool scan_properties(int fd, uint32_t id, uint32_t type, uint32_t *result
 	return true;
 }
 
-bool get_drm_connector_props(int fd, uint32_t id, union wlr_drm_connector_props *out) {
+bool get_drm_connector_props(int fd, uint32_t id,
+		union wlr_drm_connector_props *out) {
 	return scan_properties(fd, id, DRM_MODE_OBJECT_CONNECTOR, out->props,
 		connector_info, sizeof(connector_info) / sizeof(connector_info[0]));
 }
@@ -103,7 +105,8 @@ bool get_drm_plane_props(int fd, uint32_t id, union wlr_drm_plane_props *out) {
 }
 
 bool get_drm_prop(int fd, uint32_t obj, uint32_t prop, uint64_t *ret) {
-	drmModeObjectProperties *props = drmModeObjectGetProperties(fd, obj, DRM_MODE_OBJECT_ANY);
+	drmModeObjectProperties *props =
+		drmModeObjectGetProperties(fd, obj, DRM_MODE_OBJECT_ANY);
 	if (!props) {
 		return false;
 	}

include/backend/drm/properties.h

@@ -14,12 +14,13 @@ union wlr_drm_connector_props {
 	struct {
 		uint32_t edid;
 		uint32_t dpms;
+		uint32_t link_status; // not guaranteed to exist
 
 		// atomic-modesetting only
 
 		uint32_t crtc_id;
 	};
-	uint32_t props[3];
+	uint32_t props[4];
 };
 
 union wlr_drm_crtc_props {