drm/sun4i: don't add components that are already in the queue

Even though the components framework can handle duplicate entries,
the extra entries cause a lot more debug messages to be generated,
which would be confusing to developers not familiar with our driver
and the framework in general.

Instead, we can scan the relatively small queue and check if the
component to be added is already queued up. Since the display
pipelines are symmetrical (not considering the third display
pipeline on the A80), and we add components level by level, when
we get to the second instance at the same level, any shared downstream
components would already be in the queue.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171014040252.9621-2-wens@csie.org

drivers/gpu/drm/sun4i/sun4i_drv.c

@@ -226,6 +226,18 @@ struct endpoint_list {
 	struct list_head list;
 };
 
+static bool node_is_in_list(struct list_head *endpoints,
+			    struct device_node *node)
+{
+	struct endpoint_list *endpoint;
+
+	list_for_each_entry(endpoint, endpoints, list)
+		if (endpoint->node == node)
+			return true;
+
+	return false;
+}
+
 static int sun4i_drv_add_endpoints(struct device *dev,
 				   struct list_head *endpoints,
 				   struct component_match **match,
@@ -292,6 +304,10 @@ static int sun4i_drv_add_endpoints(struct device *dev,
 			}
 		}
 
+		/* skip downstream node if it is already in the queue */
+		if (node_is_in_list(endpoints, remote))
+			continue;
+
 		/* Add downstream nodes to the queue */
 		endpoint = kzalloc(sizeof(*endpoint), GFP_KERNEL);
 		if (!endpoint) {