libcamera: Add members to MediaEntity to support ancillary entities

With kernel support for ancillary links, we can describe the
relationship between two devices represented individually as instances
of MediaEntity. As the only property of that relationship is its
existence, describe those relationships in libcamera simply as a
vector of MediaEntity pointers to the ancillary devices.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Daniel Scally <djrscally@gmail.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
diff --git a/include/libcamera/internal/media_object.h b/include/libcamera/internal/media_object.h
index 90c6359..b157296 100644
--- a/include/libcamera/internal/media_object.h
+++ b/include/libcamera/internal/media_object.h
@@ -104,6 +104,7 @@
 	unsigned int deviceMinor() const { return minor_; }
 
 	const std::vector<MediaPad *> &pads() const { return pads_; }
+	const std::vector<MediaEntity *> ancillaryEntities() const { return ancillaryEntities_; }
 
 	const MediaPad *getPadByIndex(unsigned int index) const;
 	const MediaPad *getPadById(unsigned int id) const;
@@ -120,6 +121,8 @@
 
 	void addPad(MediaPad *pad);
 
+	void addAncillaryEntity(MediaEntity *ancillaryEntity);
+
 	std::string name_;
 	unsigned int function_;
 	unsigned int flags_;
@@ -129,6 +132,7 @@
 	unsigned int minor_;
 
 	std::vector<MediaPad *> pads_;
+	std::vector<MediaEntity *> ancillaryEntities_;
 };
 
 } /* namespace libcamera */
diff --git a/src/libcamera/media_object.cpp b/src/libcamera/media_object.cpp
index f425d04..c78f475 100644
--- a/src/libcamera/media_object.cpp
+++ b/src/libcamera/media_object.cpp
@@ -423,4 +423,19 @@
 	pads_.push_back(pad);
 }
 
+/**
+ * \brief Add a MediaEntity to the list of ancillary entities
+ * \param[in] ancillaryEntity The instance of MediaEntity to add
+ */
+void MediaEntity::addAncillaryEntity(MediaEntity *ancillaryEntity)
+{
+	ancillaryEntities_.push_back(ancillaryEntity);
+}
+
+/**
+ * \fn MediaEntity::ancillaryEntities()
+ * \brief Retrieve all ancillary entities of the entity
+ * \return The list of the entity's ancillary entities
+ */
+
 } /* namespace libcamera */