[libcamera-devel] [RFC 6/8] libcamera: stream: Add operation to map buffers

[Jacopo Mondi]

Add and operation to map external buffers provided by applications in
a Request to the Stream's internal buffers used by the pipeline handlers
to interact with the video device.

For streams using internal memory allocation, the two buffers are the
same as applications effectively use Buffers from the Stream's pool
where the video device memory has been exported to.

Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
---
 include/libcamera/buffer.h |  1 +
 include/libcamera/stream.h |  5 +++
 src/libcamera/stream.cpp   | 66 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+)

diff --git a/include/libcamera/buffer.h b/include/libcamera/buffer.h
index 260a62e9e77e..d5d3dc90a096 100644
--- a/include/libcamera/buffer.h
+++ b/include/libcamera/buffer.h
@@ -59,6 +59,7 @@ private:
 	friend class BufferPool;
 	friend class PipelineHandler;
 	friend class Request;
+	friend class Stream;
 	friend class V4L2VideoDevice;
 
 	void cancel();
diff --git a/include/libcamera/stream.h b/include/libcamera/stream.h
index 796f1aff2602..4c034c113ddb 100644
--- a/include/libcamera/stream.h
+++ b/include/libcamera/stream.h
@@ -85,6 +85,8 @@ public:
 	const StreamConfiguration &configuration() const { return configuration_; }
 	MemoryType memoryType() const { return memoryType_; }
 
+	Buffer *mapBuffer(Buffer *requestBuffer);
+
 protected:
 	friend class Camera;
 
@@ -94,6 +96,9 @@ protected:
 	BufferPool bufferPool_;
 	StreamConfiguration configuration_;
 	MemoryType memoryType_;
+
+	std::vector<Buffer *> mappableBuffers_;
+	std::map<unsigned int, Buffer *> bufferMaps_;
 };
 
 } /* namespace libcamera */
diff --git a/src/libcamera/stream.cpp b/src/libcamera/stream.cpp
index b6292427d3a2..f36336857ad6 100644
--- a/src/libcamera/stream.cpp
+++ b/src/libcamera/stream.cpp
@@ -13,6 +13,8 @@
 #include <iomanip>
 #include <sstream>
 
+#include <libcamera/request.h>
+
 #include "log.h"
 
 /**
@@ -445,6 +447,26 @@ void Stream::createBuffers(unsigned int count)
 		return;
 
 	bufferPool_.createBuffers(count);
+
+	/* Streams with internal memory usage do not need buffer mapping. */
+	if (memoryType_ == InternalMemory)
+		return;
+
+	/*
+	 * Prepare for buffer mapping by queuing all buffers from the internal
+	 * pool. Each external buffer presented by application will be mapped
+	 * on an internal one.
+	 */
+	mappableBuffers_.clear();
+	for (Buffer &buffer : bufferPool_.buffers()) {
+		/* Reserve all planes to support mapping multiplanar buffers. */
+		buffer.planes().clear();
+		/* \todo: I would use VIDEO_MAX_PLANES but that's V4L2 stuff.. */
+		for (unsigned int i = 0; i < 3; ++i)
+			buffer.planes().emplace_back();
+
+		mappableBuffers_.push_back(&buffer);
+	}
 }
 
 /**
@@ -457,6 +479,50 @@ void Stream::destroyBuffers()
 	createBuffers(0);
 }
 
+/**
+ * \brief Map the buffer an application has associated with a Request to an
+ * internl one
+ *
+ * \todo Rewrite documentation
+ * If the Stream uses external memory, we need to map the externally
+ * provided buffer to an internal one, trying to keep a best effort
+ * association based on the Buffer's last usage time.
+ * External and internal buffers are associated by using the dmabuf
+ * fds as key.
+ */
+Buffer *Stream::mapBuffer(Buffer *requestBuffer)
+{
+	/*
+	 * \todo Multiplane APIs have one fd per plane, the key should be
+	 * hashed using all the planes fds.
+	 */
+	unsigned int key = requestBuffer->planes()[0].dmabuf();
+
+	/* If the buffer has already been mapped, just return it. */
+	auto mapped = bufferMaps_.find(key);
+	if (mapped != bufferMaps_.end())
+		return mapped->second;
+
+	/*
+	 * Remove the last recently used buffer from the circular list and
+	 * use it for mapping.
+	 */
+	auto mappable = mappableBuffers_.begin();
+	Buffer *buffer = *mappable;
+	mappableBuffers_.erase(mappable);
+	mappableBuffers_.push_back(buffer);
+
+	/* \todo: Support multiplanar external buffers. */
+	buffer->planes()[0].setDmabuf(key, 0);
+
+	/* Pipeline handlers use request_ at buffer completion time. */
+	buffer->request_ = requestBuffer->request();
+
+	bufferMaps_[key] = buffer;
+
+	return buffer;
+}
+
 /**
  * \var Stream::bufferPool_
  * \brief The pool of buffers associated with the stream
-- 
2.21.0