libcamera: media_device: Add helper to return matching entities

Provide a helper on the MediaDevice to return a list of all
available entities which match a given function in the graph.

As a drive by, also fix a whitespace error in the documentation of
MediaDevice::setupLink.

Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Stefan Klug <stefan.klug@ideasonboard.com>

include/libcamera/internal/media_device.h

@@ -55,6 +55,8 @@ public:
 
 	Signal<> disconnected;
 
+	std::vector<MediaEntity *> locateEntities(unsigned int function);
+
 protected:
 	std::string logPrefix() const override;
 

src/libcamera/media_device.cpp

@@ -794,7 +794,7 @@ void MediaDevice::fixupEntityFlags(struct media_v2_entity *entity)
  * low-level link setup as it performs no checks on the validity of the \a
  * flags, and assumes that the supplied \a flags are valid for the link (e.g.
  * immutable links cannot be disabled).
-*
+ *
  * \sa MediaLink::setEnabled(bool enable)
  *
  * \return 0 on success or a negative error code otherwise
@@ -829,4 +829,26 @@ int MediaDevice::setupLink(const MediaLink *link, unsigned int flags)
 	return 0;
 }
 
+/**
+ * \brief Identify all entities of a common function in the MediaDevice
+ * \param[in] function The entity function to search for
+ *
+ * Search all entities within the graph of the MediaDevice and return
+ * a vector of those which match the given function.
+ *
+ * \return A vector of matching entities
+ */
+std::vector<MediaEntity *> MediaDevice::locateEntities(unsigned int function)
+{
+	std::vector<MediaEntity *> found;
+
+	/* Gather all the entities matching the function they expose. */
+	for (MediaEntity *entity : entities()) {
+		if (entity->function() == function)
+			found.push_back(entity);
+	}
+
+	return found;
+}
+
 } /* namespace libcamera */