Re: [PATCHv3] media: venus: provide video device lock

[Sergey Senozhatsky <senozhatsky@chromium.org>]

On (23/05/25 09:22), Hans Verkuil wrote:
> >> Since these are m2m devices, I think this should set vfh->m2m_ctx->q_lock
> >> instead.
> >>
> >> The vb2_queue is per filehandle for such devices, so by just setting
> >> vdev->lock you will have all vb2_queues use the same mutex.
> >>
> >> Instead the struct v4l2_m2m_ctx q_lock pointer, if set, will use that
> >> mutex for all vb2 operations.
> >>
> >> I think you can set it to the 'lock' mutex in struct venus_inst.
> > 
> > IIUC, the suggestion is to use the 'lock' in struct venus_inst while
> > initializing the queue. This might lead to deadlock as the same lock is used
> > during vb2 operations in driver. Might be introducing a new lock for this
> > purpose in struct venus_inst would do, unless we are trying to serialize at
> > video device (or core) context.
> 
> For the record, I have not analyzed how that lock is used in the driver,
> so if a new mutex has to be added to venus_inst rather than reusing the
> existing one, then that's fine by me.
> 
> But it should be a instance-specific mutex, not one at the device level.

Thanks for your help Hans. I added a per-instance queue mutex [1], so if
no one sees any problems with it then I can send a formal patch later on.

[1] https://lore.kernel.org/linux-media/20230525005312.GC30543@google.com