media: entity: Add iterator for entity data links

Iterating over the links for an entity is a somewhat common need
through the media subsystem, but generally the assumption is that
they will all be data links. To meet that assumption add a new macro
that iterates through an entity's links and skips non-data links.
Signed-off-by: Daniel Scally <djrscally@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/mc/mc-entity.c

@@ -9,6 +9,7 @@
  */
 
 #include <linux/bitmap.h>
+#include <linux/list.h>
 #include <linux/property.h>
 #include <linux/slab.h>
 #include <media/media-entity.h>
@@ -1051,3 +1052,18 @@ struct media_link *media_create_ancillary_link(struct media_entity *primary,
 	return link;
 }
 EXPORT_SYMBOL_GPL(media_create_ancillary_link);
+
+struct media_link *__media_entity_next_link(struct media_entity *entity,
+					    struct media_link *link,
+					    unsigned long link_type)
+{
+	link = link ? list_next_entry(link, list)
+		    : list_first_entry(&entity->links, typeof(*link), list);
+
+	list_for_each_entry_from(link, &entity->links, list)
+		if ((link->flags & MEDIA_LNK_FL_LINK_TYPE) == link_type)
+			return link;
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(__media_entity_next_link);

include/media/media-entity.h

@@ -1140,4 +1140,34 @@ struct media_link *
 media_create_ancillary_link(struct media_entity *primary,
 			    struct media_entity *ancillary);
 
+/**
+ * __media_entity_next_link() - Iterate through a &media_entity's links
+ *
+ * @entity:	pointer to the &media_entity
+ * @link:	pointer to a &media_link to hold the iterated values
+ * @link_type:	one of the MEDIA_LNK_FL_LINK_TYPE flags
+ *
+ * Return the next link against an entity matching a specific link type. This
+ * allows iteration through an entity's links whilst guaranteeing all of the
+ * returned links are of the given type.
+ */
+struct media_link *__media_entity_next_link(struct media_entity *entity,
+					    struct media_link *link,
+					    unsigned long link_type);
+
+/**
+ * for_each_media_entity_data_link() - Iterate through an entity's data links
+ *
+ * @entity:	pointer to the &media_entity
+ * @link:	pointer to a &media_link to hold the iterated values
+ *
+ * Iterate over a &media_entity's data links
+ */
+#define for_each_media_entity_data_link(entity, link)			\
+	for (link = __media_entity_next_link(entity, NULL,		\
+					     MEDIA_LNK_FL_DATA_LINK);	\
+	     link;							\
+	     link = __media_entity_next_link(entity, link,		\
+					     MEDIA_LNK_FL_DATA_LINK))
+
 #endif