v4l2: v4l2_camera: Don't use libcamera::Semaphore for available buffers

In V4L2, a blocked dqbuf should not not also block a streamoff. This
means that on streamoff, the blocked dqbuf must return (with error). We
cannot do this with the libcamera semaphore, so pull out the necessary
components of a semaphore, and put them into V4L2Camera, so that dqbuf
from V4L2CameraProxy can wait on a disjunct condition of the
availability of the semaphore or the stopping of the stream.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/src/v4l2/v4l2_camera.h b/src/v4l2/v4l2_camera.h
index ee53c2b0..515e9060 100644
--- a/src/v4l2/v4l2_camera.h
+++ b/src/v4l2/v4l2_camera.h
@@ -57,9 +57,10 @@ public:
 
 	int qbuf(unsigned int index);
 
-	bool isRunning();
+	void waitForBufferAvailable();
+	bool isBufferAvailable();
 
-	Semaphore bufferSema_;
+	bool isRunning();
 
 private:
 	void requestComplete(Request *request);
@@ -76,6 +77,10 @@ private:
 	std::deque<std::unique_ptr<Buffer>> completedBuffers_;
 
 	int efd_;
+
+	Mutex bufferMutex_;
+	std::condition_variable bufferCV_;
+	unsigned int bufferAvailableCount_;
 };
 
 #endif /* __V4L2_CAMERA_H__ */