[PATCH 38/55] media: mc-entity: Add a new helper function to get a remote pad for a pad

[Paul Elder]

From: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

The newly added media_entity_remote_source_pad() helper function handles
use cases where the entity has a link enabled uniqueness constraint
covering all pads. There are use cases where the constraint covers a
specific pad only. Add a new media_pad_remote_pad() function to handle
this. It operates as media_entity_remote_source_pad(), but on a given
pad instead of on the entity.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 Documentation/driver-api/media/mc-core.rst |  4 +--
 drivers/media/mc/mc-entity.c               | 31 ++++++++++++++++++++++
 include/media/media-entity.h               | 18 +++++++++++++
 3 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/Documentation/driver-api/media/mc-core.rst b/Documentation/driver-api/media/mc-core.rst
index a2d1e32e3abb..83c3bdbf67be 100644
--- a/Documentation/driver-api/media/mc-core.rst
+++ b/Documentation/driver-api/media/mc-core.rst
@@ -186,8 +186,8 @@ is required and the graph structure can be freed normally.
 
 Helper functions can be used to find a link between two given pads, or a pad
 connected to another pad through an enabled link
-(:c:func:`media_entity_find_link()`, :c:func:`media_entity_remote_pad()` and
-:c:func:`media_entity_remote_source_pad()`).
+(:c:func:`media_entity_find_link()`, :c:func:`media_entity_remote_pad()`,
+:c:func:`media_entity_remote_source_pad()` and :c:func:`media_pad_remote_pad()`).
 
 Use count and power handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/drivers/media/mc/mc-entity.c b/drivers/media/mc/mc-entity.c
index 1febf5a86be6..6429b0510bfb 100644
--- a/drivers/media/mc/mc-entity.c
+++ b/drivers/media/mc/mc-entity.c
@@ -958,6 +958,37 @@ media_entity_remote_pad_unique(const struct media_entity *entity,
 }
 EXPORT_SYMBOL_GPL(media_entity_remote_pad_unique);
 
+struct media_pad *media_pad_remote_pad(const struct media_pad *pad)
+{
+	struct media_pad *found_pad = NULL;
+	struct media_link *link;
+
+	list_for_each_entry(link, &pad->entity->links, list) {
+		struct media_pad *remote_pad;
+
+		if (!(link->flags & MEDIA_LNK_FL_ENABLED))
+			continue;
+
+		if (link->sink == pad)
+			remote_pad = link->source;
+		else if (link->source == pad)
+			remote_pad = link->sink;
+		else
+			continue;
+
+		if (found_pad)
+			return ERR_PTR(-ENOTUNIQ);
+
+		found_pad = remote_pad;
+	}
+
+	if (!found_pad)
+		return ERR_PTR(-ENOLINK);
+
+	return found_pad;
+}
+EXPORT_SYMBOL_GPL(media_pad_remote_pad);
+
 static void media_interface_init(struct media_device *mdev,
 				 struct media_interface *intf,
 				 u32 gobj_type,
diff --git a/include/media/media-entity.h b/include/media/media-entity.h
index 33d5f52719a0..bfe6a7b10a68 100644
--- a/include/media/media-entity.h
+++ b/include/media/media-entity.h
@@ -904,6 +904,24 @@ media_entity_remote_source_pad(const struct media_entity *entity)
 	return media_entity_remote_pad_unique(entity, MEDIA_PAD_FL_SOURCE);
 }
 
+/**
+ * media_pad_remote_pad - Find a remote pad connected to a pad
+ * @pad: The pad
+ *
+ * Search for and return a remote pad connected to @pad through an enabled
+ * link. If multiple (or no) remote pads are found, an error is returned.
+ *
+ * The uniqueness constraint makes this helper function suitable for entities
+ * that support a single active source at a time on a given pad.
+ *
+ * Return: A pointer to the remote pad, or one of the following error pointers
+ * if an error occurs:
+ *
+ * * -ENOTUNIQ - Multiple links are enabled
+ * * -ENOLINK - No connected pad found
+ */
+struct media_pad *media_pad_remote_pad(const struct media_pad *pad);
+
 /**
  * media_entity_is_streaming - Test if an entity is part of a streaming pipeline
  * @entity: The entity
-- 
2.30.2