Re: [RFC PATCH v11 6/9] media: tegra: Add Tegra210 Video input driver

[Sowjanya Komatineni]

On 4/30/20 7:13 AM, Dmitry Osipenko wrote:
> 30.04.2020 17:02, Dmitry Osipenko ÐÐÑÐÑ:
> > 30.04.2020 16:56, Dmitry Osipenko ÐÐÑÐÑ:
> > > 30.04.2020 01:00, Sowjanya Komatineni ÐÐÑÐÑ:
> > > > +static int chan_capture_kthread_finish(void *data)
> > > > +{
> > > > +	struct tegra_vi_channel *chan = data;
> > > > +	struct tegra_channel_buffer *buf;
> > > > +
> > > > +	set_freezable();
> > > > +
> > > > +	while (1) {
> > > > +		try_to_freeze();
> > > I guess it won't be great to freeze in the middle of a capture process, so:
> > > 		if (list_empty(&chan->done))
> > > 			try_to_freeze();
> > And here should be some locking protection in order not race with the
> > chan_capture_kthread_start because kthread_finish could freeze before
> > kthread_start.
> Or maybe both start / finish threads should simply be allowed to freeze
> only when both capture and done lists are empty.
>
> if (list_empty(&chan->capture) &&
>      list_empty(&chan->done))
> 	try_to_freeze();

good to freeze when not in middle of the frame capture but why should we 
not allow freeze in between captures?

Other drivers do allow freeze in between frame captures.

I guess we can freeze before dequeue for capture and in finish thread we 
can freeze after capture done. This also don't need to check for 
list_empty with freeze to allow between frame captures.