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, 31 insertions, 3 deletions

diff --git a/src/v4l2/v4l2_camera.cpp b/src/v4l2/v4l2_camera.cpp
index 177b1ea5..f7df9b85 100644
--- a/src/v4l2/v4l2_camera.cpp
+++ b/src/v4l2/v4l2_camera.cpp
@@ -18,7 +18,7 @@ LOG_DECLARE_CATEGORY(V4L2Compat);
 
 V4L2Camera::V4L2Camera(std::shared_ptr<Camera> camera)
 	: camera_(camera), isRunning_(false), bufferAllocator_(nullptr),
-	  efd_(-1)
+	  efd_(-1), bufferAvailableCount_(0)
 {
 	camera_->requestCompleted.connect(this, &V4L2Camera::requestComplete);
 }
@@ -100,7 +100,11 @@ void V4L2Camera::requestComplete(Request *request)
 	if (ret != sizeof(data))
 		LOG(V4L2Compat, Error) << "Failed to signal eventfd POLLIN";
 
-	bufferSema_.release();
+	{
+		MutexLocker locker(bufferMutex_);
+		bufferAvailableCount_++;
+	}
+	bufferCV_.notify_all();
 }
 
 int V4L2Camera::configure(StreamConfiguration *streamConfigOut,
@@ -192,7 +196,11 @@ int V4L2Camera::streamOff()
 	if (ret < 0)
 		return ret == -EACCES ? -EBUSY : ret;
 
-	isRunning_ = false;
+	{
+		MutexLocker locker(bufferMutex_);
+		isRunning_ = false;
+	}
+	bufferCV_.notify_all();
 
 	return 0;
 }
@@ -228,6 +236,26 @@ int V4L2Camera::qbuf(unsigned int index)
 	return 0;
 }
 
+void V4L2Camera::waitForBufferAvailable()
+{
+	MutexLocker locker(bufferMutex_);
+	bufferCV_.wait(locker, [&] {
+			       return bufferAvailableCount_ >= 1 || !isRunning_;
+		       });
+	if (isRunning_)
+		bufferAvailableCount_--;
+}
+
+bool V4L2Camera::isBufferAvailable()
+{
+	MutexLocker locker(bufferMutex_);
+	if (bufferAvailableCount_ < 1)
+		return false;
+
+	bufferAvailableCount_--;
+	return true;
+}
+
 bool V4L2Camera::isRunning()
 {
 	return isRunning_;