RASPBERRYPI ONLY: libcamera: v4l2_videodevice: Limit number of queued buffers

V4L2 only allows upto VIDEO_MAX_FRAME frames to be queued at a time, so
if we reach this limit, store the framebuffers in a pending queue, and
try to enqueue once a buffer has been dequeued.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>

Author: naushir

include/libcamera/internal/v4l2_videodevice.h

@@ -12,6 +12,7 @@
 #include <memory>
 #include <optional>
 #include <ostream>
+#include <queue>
 #include <stdint.h>
 #include <string>
 #include <unordered_set>
@@ -267,6 +268,8 @@ class V4L2VideoDevice : public V4L2Device
 	void bufferAvailable();
 	FrameBuffer *dequeueBuffer();
 
+	int queueToDevice(FrameBuffer *buffer);
+
 	void watchdogExpired();
 
 	template<typename T>
@@ -282,6 +285,7 @@ class V4L2VideoDevice : public V4L2Device
 
 	V4L2BufferCache *cache_;
 	std::map<unsigned int, FrameBuffer *> queuedBuffers_;
+	std::queue<FrameBuffer *> pendingBuffersToQueue_;
 
 	EventNotifier *fdBufferNotifier_;