libcamera: pipeline_handler: Simplify request completion

libcamera guarantees that requests complete in sequence. This
requirement is currently pushed down to pipeline handlers. Three out of
four of our pipeline handlers implement that requirement based on the
sole assumption that buffers will always complete in sequeuence, while
the IPU3 pipeline handler implements a more complex logic.

It turns out that the logic can be moved to the base PipelineHandler
class with support from the Request class. Do so to simplify the
pipeline handlers.

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

src/libcamera/pipeline/vimc.cpp

@@ -376,7 +376,7 @@ int VimcCameraData::init(MediaDevice *media)
 
 void VimcCameraData::bufferReady(Buffer *buffer)
 {
-	Request *request = queuedRequests_.front();
+	Request *request = buffer->request();
 
 	pipe_->completeBuffer(camera_, request, buffer);
 	pipe_->completeRequest(camera_, request);