libcamera: v4l2_device: Create device from entity name

Add a static method to V4L2Device class to create a V4L2Device instance
from a media entity name.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>

src/libcamera/include/v4l2_device.h

@@ -22,6 +22,7 @@ namespace libcamera {
 class Buffer;
 class BufferPool;
 class EventNotifier;
+class MediaDevice;
 class MediaEntity;
 
 struct V4L2Capability final : v4l2_capability {
@@ -136,6 +137,9 @@ public:
 	int streamOn();
 	int streamOff();
 
+	static V4L2Device *fromEntityName(const MediaDevice *media,
+					  const std::string &entity);
+
 protected:
 	std::string logPrefix() const;
 

src/libcamera/v4l2_device.cpp

@@ -19,6 +19,7 @@
 #include <libcamera/event_notifier.h>
 
 #include "log.h"
+#include "media_device.h"
 #include "media_object.h"
 #include "v4l2_device.h"
 
@@ -928,4 +929,25 @@ int V4L2Device::streamOff()
 	return 0;
 }
 
+/**
+ * \brief Create a new video device instance from \a entity in media device
+ * \a media
+ * \param[in] media The media device where the entity is registered
+ * \param[in] entity The media entity name
+ *
+ * Releasing memory of the newly created instance is responsibility of the
+ * caller of this function.
+ *
+ * \return A newly created V4L2Device on success, nullptr otherwise
+ */
+V4L2Device *V4L2Device::fromEntityName(const MediaDevice *media,
+				       const std::string &entity)
+{
+	MediaEntity *mediaEntity = media->getEntityByName(entity);
+	if (!mediaEntity)
+		return nullptr;
+
+	return new V4L2Device(mediaEntity);
+}
+
 } /* namespace libcamera */