[libcamera-devel] [PATCH v2] 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:
- Thanks to Jacopo:
  - Added missing call to cancelPendingRequests() in stop()

 src/libcamera/pipeline/uvcvideo/uvcvideo.cpp | 65 +++++++++++++++++---
 1 file changed, 55 insertions(+), 10 deletions(-)

diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
index 0f634b8da609..ee03b7ed7a7d 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>
@@ -45,6 +46,11 @@ public:
 			ControlInfoMap::Map *ctrls);
 	void bufferReady(FrameBuffer *buffer);
 
+	void queuePendingRequests();
+	void cancelPendingRequests();
+
+	std::queue<Request *> pendingRequests_;
+
 	std::unique_ptr<V4L2VideoDevice> video_;
 	Stream stream_;
 };
@@ -79,12 +85,13 @@ public:
 
 	bool match(DeviceEnumerator *enumerator) override;
 
+	int processControls(UVCCameraData *data, Request *request);
+
 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(const Camera *camera)
 	{
@@ -253,6 +260,7 @@ int PipelineHandlerUVC::start(Camera *camera, [[maybe_unused]] const ControlList
 void PipelineHandlerUVC::stop(Camera *camera)
 {
 	UVCCameraData *data = cameraData(camera);
+	data->cancelPendingRequests();
 	data->video_->streamOff();
 	data->video_->releaseBuffers();
 }
@@ -363,24 +371,59 @@ int PipelineHandlerUVC::processControls(UVCCameraData *data, Request *request)
 	return ret;
 }
 
+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();
+	}
+}
+
+void UVCCameraData::queuePendingRequests()
+{
+	PipelineHandlerUVC *pipe = static_cast<PipelineHandlerUVC *>(pipe_);
+
+	while (!pendingRequests_.empty()) {
+		Request *request = pendingRequests_.front();
+		FrameBuffer *buffer = request->findBuffer(&stream_);
+
+		int ret = pipe->processControls(this, request);
+		if (ret < 0) {
+			buffer->cancel();
+			pipe_->completeBuffer(request, buffer);
+			pipe_->completeRequest(request);
+			pendingRequests_.pop();
+			continue;
+		}
+
+		/* If we're missing v4l2 buffer slots, try again later */
+		ret = video_->queueBuffer(buffer);
+		if (ret < 0)
+			break;
+
+		pendingRequests_.pop();
+	}
+}
+
 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;
 }
@@ -668,6 +711,8 @@ void UVCCameraData::bufferReady(FrameBuffer *buffer)
 
 	pipe_->completeBuffer(request, buffer);
 	pipe_->completeRequest(request);
+
+	queuePendingRequests();
 }
 
 REGISTER_PIPELINE_HANDLER(PipelineHandlerUVC)
-- 
2.32.0