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

[Sowjanya Komatineni]

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)
> > +{
> > +     struct tegra_vi_channel *chan = data;
> > +     struct tegra_channel_buffer *buf;
> > +     int err = 0;
> > +     int caps_inflight;
> > +
> > +     set_freezable();
> > +
> > +     while (1) {
> > +             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?
>
> 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.

> > +             /*
> > +              * Frame start and MW_ACK_DONE syncpoint condition FIFOs are
> > +              * of max depth 2. So make sure max 2 capture requests are
> > +              * in process by the hardware at a time.
> > +              */
> > +             while (!(kthread_should_stop() || list_empty(&chan->capture))) {
> > +                     caps_inflight = chan->capture_reqs - chan->sequence;
> > +                     /*
> > +                      * Source is not streaming if error is non-zero.
> > +                      * So, do not dequeue buffers on capture error or when
> > +                      * syncpoint requests in FIFO are full.
> > +                      */
> > +                     if (err || caps_inflight >= SYNCPT_FIFO_DEPTH)
> > +                             break;
> > +
> > +                     /* dequeue the buffer and start capture */
> > +                     spin_lock(&chan->start_lock);
> > +                     if (list_empty(&chan->capture))
> > +                             break;
> > +                     buf = list_entry(chan->capture.next,
> > +                                      struct tegra_channel_buffer, queue);
> list_first_entry()
>
> > +                     list_del_init(&buf->queue);
> > +                     spin_unlock(&chan->start_lock);
> > +
> > +                     err = tegra_channel_capture_frame(chan, buf);
> > +                     if (err)
> > +                             vb2_queue_error(&chan->queue);
> > +             }
> > +
> > +             if (kthread_should_stop())
> > +                     break;
> > +     }
> > +
> > +     return 0;
> > +}