[libcamera-devel] [PATCH v2 2/5] libcamera: pipeline: uvcvideo: Add internal request queue

[Nícolas F. R. A. Prado]

Add an internal queue that stores requests until there are V4L2 buffer
slots available. This avoids the need to cancel requests when there is a
shortage of said buffers.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado at collabora.com>

---

Changes in v2:
- Added a counter to keep track of the number of available buffer slots
- Moved cancellation of pending requests to after video devices stop
- Added error log on failure to process controls

 src/libcamera/pipeline/uvcvideo/uvcvideo.cpp | 98 ++++++++++++++++----
 1 file changed, 81 insertions(+), 17 deletions(-)

diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
index 5977312a795d..5e73a8e682dd 100644
--- a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
+++ b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
@@ -10,6 +10,7 @@
 #include <iomanip>
 #include <math.h>
 #include <memory>
+#include <queue>
 #include <tuple>
 
 #include <libcamera/base/log.h>
@@ -46,8 +47,22 @@ public:
 			ControlInfoMap::Map *ctrls);
 	void bufferReady(FrameBuffer *buffer);
 
+	void queuePendingRequests();
+	void cancelPendingRequests();
+
+	void setAvailableBufferSlotCount(unsigned int count) { availableBufferSlotCount_ = count; }
+
 	std::unique_ptr<V4L2VideoDevice> video_;
 	Stream stream_;
+
+	std::queue<Request *> pendingRequests_;
+
+private:
+	int processControls(Request *request);
+	int processControl(ControlList *controls, unsigned int id,
+			   const ControlValue &value);
+
+	unsigned int availableBufferSlotCount_;
 };
 
 class UVCCameraConfiguration : public CameraConfiguration
@@ -83,10 +98,6 @@ public:
 private:
 	std::string generateId(const UVCCameraData *data);
 
-	int processControl(ControlList *controls, unsigned int id,
-			   const ControlValue &value);
-	int processControls(UVCCameraData *data, Request *request);
-
 	UVCCameraData *cameraData(Camera *camera)
 	{
 		return static_cast<UVCCameraData *>(camera->_d());
@@ -240,6 +251,8 @@ int PipelineHandlerUVC::start(Camera *camera, [[maybe_unused]] const ControlList
 	if (ret < 0)
 		return ret;
 
+	data->setAvailableBufferSlotCount(kUVCBufferSlotCount);
+
 	ret = data->video_->streamOn();
 	if (ret < 0) {
 		data->video_->releaseBuffers();
@@ -253,10 +266,11 @@ void PipelineHandlerUVC::stop(Camera *camera)
 {
 	UVCCameraData *data = cameraData(camera);
 	data->video_->streamOff();
+	data->cancelPendingRequests();
 	data->video_->releaseBuffers();
 }
 
-int PipelineHandlerUVC::processControl(ControlList *controls, unsigned int id,
+int UVCCameraData::processControl(ControlList *controls, unsigned int id,
 				       const ControlValue &value)
 {
 	uint32_t cid;
@@ -337,9 +351,9 @@ int PipelineHandlerUVC::processControl(ControlList *controls, unsigned int id,
 	return 0;
 }
 
-int PipelineHandlerUVC::processControls(UVCCameraData *data, Request *request)
+int UVCCameraData::processControls(Request *request)
 {
-	ControlList controls(data->video_->controls());
+	ControlList controls(video_->controls());
 
 	for (auto it : request->controls()) {
 		unsigned int id = it.first;
@@ -353,7 +367,7 @@ int PipelineHandlerUVC::processControls(UVCCameraData *data, Request *request)
 			<< "Setting control " << utils::hex(ctrl.first)
 			<< " to " << ctrl.second.toString();
 
-	int ret = data->video_->setControls(&controls);
+	int ret = video_->setControls(&controls);
 	if (ret) {
 		LOG(UVC, Error) << "Failed to set controls: " << ret;
 		return ret < 0 ? ret : -EINVAL;
@@ -365,21 +379,16 @@ int PipelineHandlerUVC::processControls(UVCCameraData *data, Request *request)
 int PipelineHandlerUVC::queueRequestDevice(Camera *camera, Request *request)
 {
 	UVCCameraData *data = cameraData(camera);
-	FrameBuffer *buffer = request->findBuffer(&data->stream_);
-	if (!buffer) {
+
+	if (!request->findBuffer(&data->stream_)) {
 		LOG(UVC, Error)
 			<< "Attempt to queue request with invalid stream";
 
 		return -ENOENT;
 	}
 
-	int ret = processControls(data, request);
-	if (ret < 0)
-		return ret;
-
-	ret = data->video_->queueBuffer(buffer);
-	if (ret < 0)
-		return ret;
+	data->pendingRequests_.push(request);
+	data->queuePendingRequests();
 
 	return 0;
 }
@@ -670,6 +679,61 @@ void UVCCameraData::bufferReady(FrameBuffer *buffer)
 
 	pipe()->completeBuffer(request, buffer);
 	pipe()->completeRequest(request);
+
+	availableBufferSlotCount_++;
+
+	queuePendingRequests();
+}
+
+void UVCCameraData::queuePendingRequests()
+{
+	while (!pendingRequests_.empty() && availableBufferSlotCount_) {
+		Request *request = pendingRequests_.front();
+		FrameBuffer *buffer = request->findBuffer(&stream_);
+
+		int ret = processControls(request);
+		if (ret < 0) {
+			LOG(UVC, Error) << "Failed to process controls with"
+					<< " error " << ret << ". Cancelling"
+					<< " buffer.";
+			buffer->cancel();
+			pipe()->completeBuffer(request, buffer);
+			pipe()->completeRequest(request);
+			pendingRequests_.pop();
+
+			continue;
+		}
+
+		ret = video_->queueBuffer(buffer);
+		if (ret < 0) {
+			LOG(UVC, Error) << "Failed to queue buffer with error "
+					<< ret << ". Cancelling buffer.";
+			buffer->cancel();
+			pipe()->completeBuffer(request, buffer);
+			pipe()->completeRequest(request);
+			pendingRequests_.pop();
+
+			continue;
+		}
+
+		availableBufferSlotCount_--;
+
+		pendingRequests_.pop();
+	}
+}
+
+void UVCCameraData::cancelPendingRequests()
+{
+	while (!pendingRequests_.empty()) {
+		Request *request = pendingRequests_.front();
+		FrameBuffer *buffer = request->findBuffer(&stream_);
+
+		buffer->cancel();
+		pipe()->completeBuffer(request, buffer);
+		pipe()->completeRequest(request);
+
+		pendingRequests_.pop();
+	}
 }
 
 REGISTER_PIPELINE_HANDLER(PipelineHandlerUVC)
-- 
2.33.0