libcamera: camera: Extend with a Stopping state

When the camera is being stop()ped, active requests will complete. These
may trigger an application to re-queue those requests to the camera but
that is not permitted, and is an error in the application.

Extend the camera state to include a stopping state which is entered as
soon as a call to stop() is made. At this point, any request queued will
be rejected with a warning, while any pending requests are either
successfully completed or cancelled.

When the pipeline handler has finished stopping, the camera state will
transition to the CameraConfigured state where it can begin to accept
requests again, and be restarted.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/camera.cpp

@@ -339,6 +339,7 @@ public:
 		CameraAvailable,
 		CameraAcquired,
 		CameraConfigured,
+		CameraStopping,
 		CameraRunning,
 	};
 
@@ -383,6 +384,7 @@ static const char *const camera_state_names[] = {
 	"Available",
 	"Acquired",
 	"Configured",
+	"Stopping",
 	"Running",
 };
 
@@ -492,6 +494,7 @@ void Camera::Private::setState(State state)
  *   node [shape = doublecircle ]; Available;
  *   node [shape = circle ]; Acquired;
  *   node [shape = circle ]; Configured;
+ *   node [shape = circle ]; Stopping;
  *   node [shape = circle ]; Running;
  *
  *   Available -> Available [label = "release()"];
@@ -504,7 +507,8 @@ void Camera::Private::setState(State state)
  *   Configured -> Configured [label = "configure(), createRequest()"];
  *   Configured -> Running [label = "start()"];
  *
- *   Running -> Configured [label = "stop()"];
+ *   Running -> Stopping [label = "stop()"];
+ *   Stopping -> Configured;
  *   Running -> Running [label = "createRequest(), queueRequest()"];
  * }
  * \enddot
@@ -524,6 +528,12 @@ void Camera::Private::setState(State state)
  * release() the camera and to get back to the Available state or start()
  * it to progress to the Running state.
  *
+ * \subsubsection Stopping
+ * The camera has been asked to stop. Pending requests are being completed or
+ * cancelled, and no new requests are permitted to be queued. The camera will
+ * transition to the Configured state when all queued requests have been
+ * returned to the application.
+ *
  * \subsubsection Running
  * The camera is running and ready to process requests queued by the
  * application. The camera remains in this state until it is stopped and moved
@@ -1067,6 +1077,8 @@ int Camera::stop()
 
 	LOG(Camera, Debug) << "Stopping capture";
 
+	d->setState(Private::CameraStopping);
+
 	d->pipe_->invokeMethod(&PipelineHandler::stop, ConnectionTypeBlocking,
 			       this);
 
@@ -1087,7 +1099,8 @@ void Camera::requestComplete(Request *request)
 	Private *const d = LIBCAMERA_D_PTR();
 
 	/* Disconnected cameras are still able to complete requests. */
-	if (d->isAccessAllowed(Private::CameraRunning, true))
+	if (d->isAccessAllowed(Private::CameraStopping, Private::CameraRunning,
+			       true))
 		LOG(Camera, Fatal) << "Trying to complete a request when stopped";
 
 	requestCompleted.emit(request);