media: entity: Add support for ancillary links

Add functions to create ancillary links, so that they don't need to
be manually created by users.

Reviewed-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Daniel Scally <[e-mail]>
Reviewed-by: Jean-Michel Hautbois <[e-mail]>
Signed-off-by: Sakari Ailus <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/mc/mc-entity.c

···
 	mutex_unlock(&mdev->graph_mutex);
 }
 EXPORT_SYMBOL_GPL(media_remove_intf_links);
+
+struct media_link *media_create_ancillary_link(struct media_entity *primary,
+					       struct media_entity *ancillary)
+{
+	struct media_link *link;
+
+	link = media_add_link(&primary->links);
+	if (!link)
+		return ERR_PTR(-ENOMEM);
+
+	link->gobj0 = &primary->graph_obj;
+	link->gobj1 = &ancillary->graph_obj;
+	link->flags = MEDIA_LNK_FL_IMMUTABLE | MEDIA_LNK_FL_ENABLED |
+		      MEDIA_LNK_FL_ANCILLARY_LINK;
+
+	/* Initialize graph object embedded in the new link */
+	media_gobj_create(primary->graph_obj.mdev, MEDIA_GRAPH_LINK,
+			  &link->graph_obj);
+
+	return link;
+}
+EXPORT_SYMBOL_GPL(media_create_ancillary_link);

include/media/media-entity.h

···
 	(((entity)->ops && (entity)->ops->operation) ?			\
 	 (entity)->ops->operation((entity) , ##args) : -ENOIOCTLCMD)
 
+/**
+ * media_create_ancillary_link() - create an ancillary link between two
+ *				   instances of &media_entity
+ *
+ * @primary:	pointer to the primary &media_entity
+ * @ancillary:	pointer to the ancillary &media_entity
+ *
+ * Create an ancillary link between two entities, indicating that they
+ * represent two connected pieces of hardware that form a single logical unit.
+ * A typical example is a camera lens controller being linked to the sensor that
+ * it is supporting.
+ *
+ * The function sets both MEDIA_LNK_FL_ENABLED and MEDIA_LNK_FL_IMMUTABLE for
+ * the new link.
+ */
+struct media_link *
+media_create_ancillary_link(struct media_entity *primary,
+			    struct media_entity *ancillary);
+
 #endif