libcamera: pipeline_handler: Split request queueing

In order to prepare to handle synchronization fences at Request
queueing time, split the PipelineHandler::queueRequest() function in
two, by creating a list of waiting requests and introducing the
doQueueRequest() function that queues requests to the device in the
order the pipeline has received them.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

include/libcamera/internal/pipeline_handler.h

@@ -8,6 +8,7 @@
 #pragma once
 
 #include <memory>
+#include <queue>
 #include <set>
 #include <string>
 #include <sys/types.h>
@@ -76,9 +77,14 @@ private:
 	void mediaDeviceDisconnected(MediaDevice *media);
 	virtual void disconnect();
 
+	void doQueueRequest(Request *request);
+	void doQueueRequests();
+
 	std::vector<std::shared_ptr<MediaDevice>> mediaDevices_;
 	std::vector<std::weak_ptr<Camera>> cameras_;
 
+	std::queue<Request *> waitingRequests_;
+
 	const char *name_;
 
 	friend class PipelineHandlerFactory;

include/libcamera/internal/tracepoints/request.tp

@@ -58,6 +58,15 @@ TRACEPOINT_EVENT_INSTANCE(
 	)
 )
 
+TRACEPOINT_EVENT_INSTANCE(
+	libcamera,
+	request,
+	request_device_queue,
+	TP_ARGS(
+		libcamera::Request *, req
+	)
+)
+
 TRACEPOINT_EVENT_INSTANCE(
 	libcamera,
 	request,