[media] media-device: supress backlinks at G_TOPOLOGY ioctl

Due to the graph traversal algorithm currently in usage, we
need a copy of all data links. Those backlinks should not be
send to userspace, as otherwise, all links there will be
duplicated.
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/media-device.c

@@ -333,6 +333,9 @@ static long __media_device_get_topology(struct media_device *mdev,
 	/* Get links and number of links */
 	i = 0;
 	media_device_for_each_link(link, mdev) {
+		if (link->is_backlink)
+			continue;
+
 		i++;
 
 		if (ret || !topo->links)

drivers/media/media-entity.c

@@ -625,6 +625,7 @@ media_create_pad_link(struct media_entity *source, u16 source_pad,
 	backlink->source = &source->pads[source_pad];
 	backlink->sink = &sink->pads[sink_pad];
 	backlink->flags = flags;
+	backlink->is_backlink = true;
 
 	/* Initialize graph object embedded at the new link */
 	media_gobj_init(sink->graph_obj.mdev, MEDIA_GRAPH_LINK,

include/media/media-entity.h

@@ -96,6 +96,7 @@ struct media_pipeline {
  * @reverse:	Pointer to the link for the reverse direction of a pad to pad
  *		link.
  * @flags:	Link flags, as defined in uapi/media.h (MEDIA_LNK_FL_*)
+ * @is_backlink: Indicate if the link is a backlink.
  */
 struct media_link {
 	struct media_gobj graph_obj;
@@ -112,6 +113,7 @@ struct media_link {
 	};
 	struct media_link *reverse;
 	unsigned long flags;
+	bool is_backlink;
 };
 
 /**