[libcamera-devel] [RFC PATCH 4/5] libcamera: pipeline: uvcvideo: Allocate metadata buffers

[Gabby George]

Perform the allocation and mapping of metadata buffers into
libcamera's virtual address space.  UVC metadata buffers cannot be
exported as DMA buffer file descriptors, so use the MappedFrameBuffer
class to map them into memory directly.  This will give the UVC
pipeline access to buffer data to extract timestamp information.

Metadata buffers are internal to the UVC pipeline, so buffer memory
should not be exposed to the user.

Signed-off-by: Gabby George <gabbymg94 at gmail.com>
---
 src/libcamera/pipeline/uvcvideo/uvcvideo.cpp | 97 +++++++++++++++++++-
 1 file changed, 95 insertions(+), 2 deletions(-)

diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
index 4470d8a2..51f30187 100644
--- a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
+++ b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
@@ -24,6 +24,7 @@
 
 #include "libcamera/internal/camera.h"
 #include "libcamera/internal/device_enumerator.h"
+#include "libcamera/internal/mapped_framebuffer.h"
 #include "libcamera/internal/media_device.h"
 #include "libcamera/internal/pipeline_handler.h"
 #include "libcamera/internal/sysfs.h"
@@ -51,11 +52,17 @@ public:
 	std::unique_ptr<V4L2VideoDevice> video_;
 	std::unique_ptr<V4L2VideoDevice> metadata_;
 	Stream stream_;
+	std::vector<std::unique_ptr<FrameBuffer>> metadataBuffers_;
+	std::map<unsigned int, MappedFrameBuffer> mappedMetadataBuffers_;
+	bool useMetadataStream_;
+
 	std::map<PixelFormat, std::vector<SizeRange>> formats_;
 
 private:
 	int initMetadata(MediaDevice *media);
 
+	const unsigned int minLengthHeaderBuf_ = 10;
+
 	bool generateId();
 
 	std::string id_;
@@ -96,6 +103,10 @@ private:
 			   const ControlValue &value);
 	int processControls(UVCCameraData *data, Request *request);
 
+	int createMetadataBuffers(Camera *camera, unsigned int count);
+	int cleanupMetadataBuffers(Camera *camera);
+	int cleanup(Camera *camera);
+
 	UVCCameraData *cameraData(Camera *camera)
 	{
 		return static_cast<UVCCameraData *>(camera->_d());
@@ -225,10 +236,66 @@ int PipelineHandlerUVC::configure(Camera *camera, CameraConfiguration *config)
 		return -EINVAL;
 
 	cfg.setStream(&data->stream_);
+	return 0;
+}
 
+int PipelineHandlerUVC::cleanupMetadataBuffers(Camera *camera)
+{
+	int ret = 0;
+	UVCCameraData *data = cameraData(camera);
+
+	ret = data->metadata_->releaseBuffers();
+	data->metadataBuffers_.clear(); //call the destructor for the frame buffers
+	data->mappedMetadataBuffers_.clear();
+	data->useMetadataStream_ = false;
+
+	return ret;
+}
+
+int PipelineHandlerUVC::cleanup(Camera *camera)
+{
+	UVCCameraData *data = cameraData(camera);
+	cleanupMetadataBuffers(camera);
+	data->video_->releaseBuffers();
 	return 0;
 }
 
+/*
+ * UVC Metadata stream does not support exporting buffers via EXPBUF,
+ * so it is necessary to create and store mmap-ed addresses.
+ * Metadata buffers are internal to libcamera. They are not, and
+ * cannot be, exposed to the user.
+ *
+ * Returns the number of buffers allocated and mapped.
+ *
+ * \return The number of buffers allocated, or a negative error code if
+ * the number of buffers allocated was not equal to "count"
+ * \retval -EINVAL if "count" buffers were not successfully allocated.
+ * \retval -ENOMEM if mmap failed.
+ */
+int PipelineHandlerUVC::createMetadataBuffers(Camera *camera, unsigned int count)
+{
+	UVCCameraData *data = cameraData(camera);
+	int ret = data->metadata_->allocateBuffers(count, &data->metadataBuffers_);
+	if (ret < 0)
+		return -EINVAL;
+
+	for (unsigned int i = 0; i < count; i++) {
+		MappedFrameBuffer mappedBuffer(data->metadataBuffers_[i].get(),
+					       MappedFrameBuffer::MapFlag::Read, true);
+		if (!mappedBuffer.isValid()) {
+			LOG(UVC, Error)
+				<< "Failed to mmap metadata buffer: "
+				<< strerror(mappedBuffer.error());
+			return mappedBuffer.error();
+		}
+
+		data->mappedMetadataBuffers_.emplace(i, std::move(mappedBuffer));
+		data->metadataBuffers_[i]->setCookie(i);
+	}
+	return ret;
+}
+
 int PipelineHandlerUVC::exportFrameBuffers(Camera *camera, Stream *stream,
 					   std::vector<std::unique_ptr<FrameBuffer>> *buffers)
 {
@@ -247,20 +314,46 @@ int PipelineHandlerUVC::start(Camera *camera, [[maybe_unused]] const ControlList
 	if (ret < 0)
 		return ret;
 
+	if (data->useMetadataStream_) {
+		if (createMetadataBuffers(camera, count) < 0) {
+			LOG(UVC, Error) << "Unable to allocate buffers for UVC metadata stream.";
+			data->useMetadataStream_ = false;
+		}
+	}
+
 	ret = data->video_->streamOn();
 	if (ret < 0) {
-		data->video_->releaseBuffers();
+		cleanup(camera);
 		return ret;
 	}
 
+	if (data->useMetadataStream_) {
+		ret = data->metadata_->streamOn();
+		if (ret) {
+			LOG(UVC, Error) << "Failed to start metadata stream";
+			return ret;
+		}
+
+		for (std::unique_ptr<FrameBuffer> &buf : data->metadataBuffers_) {
+			ret = data->metadata_->queueBuffer(buf.get());
+			if (ret < 0) {
+				cleanupMetadataBuffers(camera);
+				return ret;
+			}
+		}
+	}
 	return 0;
 }
 
 void PipelineHandlerUVC::stopDevice(Camera *camera)
 {
 	UVCCameraData *data = cameraData(camera);
+
 	data->video_->streamOff();
-	data->video_->releaseBuffers();
+
+	data->metadata_->streamOff();
+
+	cleanup(camera);
 }
 
 int PipelineHandlerUVC::processControl(ControlList *controls, unsigned int id,
-- 
2.34.1