[libcamera-devel] [RFC PATCH v2 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 | 98 +++++++++++++++++++-
 1 file changed, 96 insertions(+), 2 deletions(-)

diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
index dbe0cc8c..c8d6633f 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"
@@ -51,6 +52,9 @@ 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_;
+
 	std::map<PixelFormat, std::vector<SizeRange>> formats_;
 
 private:
@@ -96,6 +100,10 @@ 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 +233,67 @@ 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);
+
+	if (data->metadata_)
+		data->metadata_->releaseBuffers();
+	data->metadataBuffers_.clear();
+	data->mappedMetadataBuffers_.clear();
+	data->metadata_ = nullptr;
 
+	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 MappedFrameBuffer::error()
+ */
+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, Warning)
+				<< "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)
 {
@@ -249,18 +314,47 @@ int PipelineHandlerUVC::start(Camera *camera, [[maybe_unused]] const ControlList
 
 	ret = data->video_->streamOn();
 	if (ret < 0) {
-		data->video_->releaseBuffers();
+		cleanup(camera);
 		return ret;
 	}
 
+	/*
+	 * If metadata allocation fails, exit this function but
+	 * do not return a failure as video started successfully.
+	 * Fall back on using driver timestamps.
+	 */
+	if (data->metadata_) {
+		if (createMetadataBuffers(camera, count) < 0 ||
+		    data->metadata_->streamOn()) {
+			LOG(UVC, Warning)
+				<< "Metadata stream unavailable.  Using driver timestamps.";
+			data->metadata_ = nullptr;
+			return 0;
+		}
+
+		for (std::unique_ptr<FrameBuffer> &buf : data->metadataBuffers_) {
+			ret = data->metadata_->queueBuffer(buf.get());
+			if (ret < 0) {
+				LOG(UVC, Warning)
+					<< "Metadata stream unavailable.  Using driver timestamps.";
+				cleanupMetadataBuffers(camera);
+				return 0;
+			}
+		}
+	}
 	return 0;
 }
 
 void PipelineHandlerUVC::stopDevice(Camera *camera)
 {
 	UVCCameraData *data = cameraData(camera);
+
 	data->video_->streamOff();
-	data->video_->releaseBuffers();
+
+	if (data->metadata_)
+		data->metadata_->streamOff();
+
+	cleanup(camera);
 }
 
 int PipelineHandlerUVC::processControl(ControlList *controls, unsigned int id,
-- 
2.34.1