drm-backend: reduce number of drmModeGetConnector() calls

Instead of calling drmModeGetConnector() in drm_head_create()
and drm_head_update_info(), it is better to call it in
drm_backend_create_heads() and drm_backend_update_heads().
Then we can pass the drmModeConnector object as parameter.
This does not change the behavior of the code, but help us
to avoid unnecessarily calling drmModeGetConnector().

Besides that, in the future we will have support for writeback
connectors. And so drm_backend_create_heads() will be reworked
to also populate a list of writeback connectors. To make this
work, we are going to need to know if a connector is of the
writeback type or not, to know if we should call drm_head_create()
or drm_writeback_create(). We can only tell the type of connector
if we have the drmModeConnector object.

Signed-off-by: Leandro Ribeiro <leandro.ribeiro@collabora.com>

libweston/backend-drm/drm.c

@@ -2025,12 +2025,13 @@ static int
 drm_connector_assign_connector_info(struct drm_connector *connector,
 				    drmModeConnector *conn)
 {
+	assert(connector->conn != conn);
 	assert(connector->connector_id == conn->connector_id);
 
 	if (drm_connector_update_properties(connector) < 0)
 		return -1;
 
-	if (connector->conn && connector->conn != conn)
+	if (connector->conn)
 		drmModeFreeConnector(connector->conn);
 	connector->conn = conn;
 
@@ -2048,22 +2049,15 @@ drm_connector_assign_connector_info(struct drm_connector *connector,
 	return 0;
 }
 
-static int
+static void
 drm_connector_init(struct drm_backend *b, struct drm_connector *connector,
 		   uint32_t connector_id)
 {
 	connector->backend = b;
 	connector->connector_id = connector_id;
+	connector->conn = NULL;
 	connector->head = NULL;
 	connector->props_drm = NULL;
-
-	connector->conn = drmModeGetConnector(b->drm.fd, connector_id);
-	if (!connector->conn) {
-		weston_log("DRM: Could not retrieve connector.\n");
-		return -1;
-	}
-
-	return 0;
 }
 
 static void
@@ -2092,29 +2086,23 @@ drm_head_log_info(struct drm_head *head, const char *msg)
 /** Update connector and monitor information
  *
  * @param head The head to update.
+ * @param conn The DRM connector object.
+ * @returns 0 on success, -1 on failure.
  *
- * Re-reads the DRM property lists for the connector and updates monitor
+ * Updates monitor information and connection status. This may schedule a
- * information and connection status. This may schedule a heads changed call
+ * heads changed call to the user.
- * to the user.
  */
-static void
+static int
-drm_head_update_info(struct drm_head *head)
+drm_head_update_info(struct drm_head *head, drmModeConnector *conn)
 {
-	drmModeConnector *conn;
+	int ret;
-
-	conn = drmModeGetConnector(head->backend->drm.fd,
-				   head->connector.connector_id);
-	if (!conn) {
-		weston_log("DRM: getting connector info for '%s' failed.\n",
-			   head->base.name);
-		return;
-	}
 
-	if (drm_connector_assign_connector_info(&head->connector, conn) < 0)
+	ret = drm_connector_assign_connector_info(&head->connector, conn);
-		drmModeFreeConnector(conn);
 
 	if (head->base.device_changed)
 		drm_head_log_info(head, "updated");
+
+	return ret;
 }
 
 /**
@@ -2124,34 +2112,30 @@ drm_head_update_info(struct drm_head *head)
  * to Weston's head list.
  *
  * @param backend Weston backend structure
- * @param connector_id DRM connector ID for the head
+ * @param conn DRM connector object
  * @param drm_device udev device pointer
- * @returns The new head, or NULL on failure.
+ * @returns 0 on success, -1 on failure
  */
-static struct drm_head *
+static int
-drm_head_create(struct drm_backend *backend, uint32_t connector_id,
+drm_head_create(struct drm_backend *backend, drmModeConnector *conn,
 		struct udev_device *drm_device)
 {
 	struct drm_head *head;
-	drmModeConnector *conn;
 	char *name;
 	int ret;
 
 	head = zalloc(sizeof *head);
 	if (!head)
-		return NULL;
+		return -1;
 
 	head->backend = backend;
 
-	ret = drm_connector_init(backend, &head->connector, connector_id);
+	drm_connector_init(backend, &head->connector, conn->connector_id);
-	if (ret < 0)
-		goto err;
 	head->connector.head = head;
-	conn = head->connector.conn;
 
 	name = make_connector_name(conn);
 	if (!name)
-		goto err_name;
+		goto err;
 
 	weston_head_init(&head->base, name);
 	free(name);
@@ -2175,15 +2159,14 @@ drm_head_create(struct drm_backend *backend, uint32_t connector_id,
 	weston_compositor_add_head(backend->compositor, &head->base);
 	drm_head_log_info(head, "found");
 
-	return head;
+	return 0;
 
 err_assign:
 	weston_head_release(&head->base);
-err_name:
-	drm_connector_fini(&head->connector);
 err:
+	drm_connector_fini(&head->connector);
 	free(head);
-	return NULL;
+	return -1;
 }
 
 static void
@@ -2250,9 +2233,9 @@ drm_output_create(struct weston_compositor *compositor, const char *name)
 static int
 drm_backend_create_heads(struct drm_backend *b, struct udev_device *drm_device)
 {
-	struct drm_head *head;
 	drmModeRes *resources;
-	int i;
+	drmModeConnector *conn;
+	int i, ret;
 
 	resources = drmModeGetResources(b->drm.fd);
 	if (!resources) {
@@ -2268,10 +2251,15 @@ drm_backend_create_heads(struct drm_backend *b, struct udev_device *drm_device)
 	for (i = 0; i < resources->count_connectors; i++) {
 		uint32_t connector_id = resources->connectors[i];
 
-		head = drm_head_create(b, connector_id, drm_device);
+		conn = drmModeGetConnector(b->drm.fd, connector_id);
-		if (!head) {
+		if (!conn)
+			continue;
+
+		ret = drm_head_create(b, conn, drm_device);
+		if (ret < 0) {
 			weston_log("DRM: failed to create head for connector %d.\n",
 				   connector_id);
+			drmModeFreeConnector(conn);
 		}
 	}
 
@@ -2284,10 +2272,11 @@ static void
 drm_backend_update_heads(struct drm_backend *b, struct udev_device *drm_device)
 {
 	drmModeRes *resources;
+	drmModeConnector *conn;
 	struct weston_head *base, *next;
 	struct drm_head *head;
 	uint32_t connector_id;
-	int i;
+	int i, ret;
 
 	resources = drmModeGetResources(b->drm.fd);
 	if (!resources) {
@@ -2299,14 +2288,22 @@ drm_backend_update_heads(struct drm_backend *b, struct udev_device *drm_device)
 	for (i = 0; i < resources->count_connectors; i++) {
 		connector_id = resources->connectors[i];
 
+		conn = drmModeGetConnector(b->drm.fd, connector_id);
+		if (!conn)
+			continue;
+
 		head = drm_head_find_by_connector(b, connector_id);
 		if (head) {
-			drm_head_update_info(head);
+			ret = drm_head_update_info(head, conn);
+			if (ret < 0)
+				drmModeFreeConnector(conn);
 		} else {
-			head = drm_head_create(b, connector_id, drm_device);
+			ret = drm_head_create(b, conn, drm_device);
-			if (!head)
+			if (ret < 0) {
 				weston_log("DRM: failed to create head for hot-added connector %d.\n",
 					   connector_id);
+				drmModeFreeConnector(conn);
+			}
 		}
 	}