libcamera: stream: Map external buffers to indexes

Add and use an operation to assign to Buffer representing external
memory locations an index at queueRequest() time. The index is used to
identify the memory buffer to be queued to the video device once the
buffer will be queued in a Request.

In order to minimize relocations in the V4L2 backend, this method
provides a best-effort caching mechanisms that attempts to reuse
BufferMemory previously mapped to the buffer's dmabuf file descriptors,
if any.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/camera.cpp

@@ -800,6 +800,7 @@ Request *Camera::createRequest(uint64_t cookie)
  * \retval -ENODEV The camera has been disconnected from the system
  * \retval -EACCES The camera is not running so requests can't be queued
  * \retval -EINVAL The request is invalid
+ * \retval -ENOMEM No buffer memory was available to handle the request
  */
 int Camera::queueRequest(Request *request)
 {
@@ -818,6 +819,16 @@ int Camera::queueRequest(Request *request)
 			return -EINVAL;
 		}
 
+		if (stream->memoryType() == ExternalMemory) {
+			int index = stream->mapBuffer(buffer);
+			if (index < 0) {
+				LOG(Camera, Error) << "No buffer memory available";
+				return -ENOMEM;
+			}
+
+			buffer->index_ = index;
+		}
+
 		buffer->mem_ = &stream->buffers()[buffer->index_];
 	}
 
@@ -901,7 +912,14 @@ int Camera::stop()
  */
 void Camera::requestComplete(Request *request)
 {
-	requestCompleted.emit(request, request->bufferMap_);
+	for (auto it : request->buffers()) {
+		Stream *stream = it.first;
+		Buffer *buffer = it.second;
+		if (stream->memoryType() == ExternalMemory)
+			stream->unmapBuffer(buffer);
+	}
+
+	requestCompleted.emit(request, request->buffers());
 	delete request;
 }