[libcamera-devel] [RFC PATCH] qcam: Fix IPU3 camera switching

[Kieran Bingham]

On the IPU3 we will disallow acquiring a second camera while one is
active.  This prevents us from doing a camera switch between the
available cameras.

Re-instate this facility by ensuring we release the current camera
before attempting to acquire the new camera.

Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
---

QCam is broken on IPU3 in that once one camera is running, we can't swap
to the other without closing qcam (or swapping to a non IPU3 camera).

This seems a bit of a pain - but here's a potential fix.

Since writing this patch (some time ago) I know think that trying to
reaquire the previous camera if the switch fails might be wrong.

I wonder if we should just leave the camera halted, with our 'no-image'
logo displayed, and wait. But the only way to 'fix' this would be for
the user to choose a new camera, there's no current option to retry
acquiring a camera...


 src/qcam/main_window.cpp | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/qcam/main_window.cpp b/src/qcam/main_window.cpp
index 7433d647e8a0..487f522748ca 100644
--- a/src/qcam/main_window.cpp
+++ b/src/qcam/main_window.cpp
@@ -269,11 +269,6 @@ void MainWindow::switchCamera(int index)
 
 	const std::shared_ptr<Camera> &cam = cameras[index];
 
-	if (cam->acquire()) {
-		qInfo() << "Failed to acquire camera" << cam->id().c_str();
-		return;
-	}
-
 	qInfo() << "Switching to camera" << cam->id().c_str();
 
 	/*
@@ -283,7 +278,26 @@ void MainWindow::switchCamera(int index)
 	startStopAction_->setChecked(false);
 
 	camera_->release();
-	camera_ = cam;
+
+	/*
+	 * Only attempt to acquire after releasing to ensure we support
+	 * pipelines which can only stream from one device at a time.
+	 *
+	 * Todo: Consider how we could acquire more than one camera
+	 *       but ensure only one could stream at a time.
+	 */
+	if (cam->acquire()) {
+		qInfo() << "Failed to acquire camera" << cam->id().c_str();
+		qInfo() << "Switching back to " << camera_->id().c_str();
+
+		if (camera_->acquire()) {
+			qInfo() << "Failed to reacquire " << camera_->id().c_str();
+			return;
+		}
+	} else {
+		/* Acquire was successful, Switch to this camera */
+		camera_ = cam;
+	}
 
 	startStopAction_->setChecked(true);
 }
-- 
2.34.1