Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver

[Sowjanya Komatineni]

On 4/6/20 1:38 PM, Sowjanya Komatineni wrote:
> On 4/6/20 1:37 PM, Dmitry Osipenko wrote:
> > External email: Use caution opening links or attachments
> >
> >
> > 06.04.2020 23:20, Sowjanya Komatineni ÐÐÑÐÑ:
> > > On 4/6/20 1:02 PM, Dmitry Osipenko wrote:
> > > > External email: Use caution opening links or attachments
> > > >
> > > >
> > > > 04.04.2020 04:25, Sowjanya Komatineni ÐÐÑÐÑ:
> > > > ...
> > > > > +static int chan_capture_kthread_start(void *data)
> > > > > +{
> > > > > +ÂÂÂÂ struct tegra_vi_channel *chan = data;
> > > > > +ÂÂÂÂ struct tegra_channel_buffer *buf;
> > > > > +ÂÂÂÂ int err = 0;
> > > > > +ÂÂÂÂ int caps_inflight;
> > > > > +
> > > > > +ÂÂÂÂ set_freezable();
> > > > > +
> > > > > +ÂÂÂÂ while (1) {
> > > > > +ÂÂÂÂÂÂÂÂÂÂÂÂ try_to_freeze();
> > > > > +
> > > > > + wait_event_interruptible(chan->start_wait,
> > > > > + !list_empty(&chan->capture) ||
> > > > > + kthread_should_stop());
> > > > Is it really okay that list_empty() isn't protected with a lock?

wakeup on thread happens either when buffer is moved to capture list or 
on stop signaling event.

So in this specific case we may not need to check for lock on capture 
list as if wakeup happens from start wait queue, then buffer is already 
moved to capture list by then.

> > > > Why wait_event is "interruptible"?
> > > To allow it to sleep until wakeup on thread it to avoid constant
> > > checking for condition even when no buffers are ready, basically to
> > > prevent blocking.
> > So the "interrupt" is for getting event about kthread_should_stop(),
> > correct?
> also to prevent blocking and to let is sleep and wakeup based on wait 
> queue to evaluate condition to proceed with the task
> >