Hi, This series is an attempt to scratch an old itch, it's problematic to support unbind and then a second call to complete in v4l2-async. When the second complete call happens a lot of things can go wrong. When v4l2-async complete callback is called multiple video devices are registered with video_register_device(). Then if a v4l2-async unbind happens they are unregistered with video_unregister_device(). Their are multiple problems with this, specially for R-Car VIN. 1. Depending on which subdevice is unbound parts of the video pipeline can still function. There are for example two CSI-2 receivers connected to two different CSI-2 buses in the pipeline. If one of the receivers are unbound the other can still function perfectly well. But with the current setup everything goes away, this is bad for operational safety. 2. The struct video_device contains a static struct device, which in turn contains a static struct kref. When the kref is release by calling video_unregister_device() and then later trying to re-register the video device video_register_device() the kref life time management kicks in and produces warnings in later kernels or OOPS in older ones. It has been discussed in the past at various conferences that it could be OK to not video_unregister_device() if a v4l2-async unbind happens. The argument against it was that user-space needed a way to check if a pipeline was completely probed or not. And this used to be that the video devices where only present if everything was available. It was agreed in principle that if an alternate way for media controller centric devices could be found to inform user-space of this fact could be found it would be OK to not unregister video devices in case of an unbind or even allow registering the video devices at probe time instead of at v4l2-async complete time. This series aims to provide such a mechanism using the media device itself to report if the media graph is complete or not. Niklas Söderlund (5): uapi/linux/media.h: add flags field to struct media_v2_topology media-device: Add a complete flag to struct media_device v4l2-async: Flag when media graph is complete mc-device.c: Report graph complete to user-space rcar-vin: Do not unregister video device when a subdevice is unbound drivers/media/mc/mc-device.c | 2 +- drivers/media/platform/rcar-vin/rcar-core.c | 5 ----- drivers/media/v4l2-core/v4l2-async.c | 5 +++++ include/media/media-device.h | 2 ++ include/uapi/linux/media.h | 4 +++- 5 files changed, 11 insertions(+), 7 deletions(-) -- 2.27.0
