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

[Sowjanya Komatineni]

On 4/30/20 11:18 AM, Sowjanya Komatineni wrote:
> On 4/30/20 10:06 AM, Sowjanya Komatineni wrote:
> > On 4/30/20 9:29 AM, Sowjanya Komatineni wrote:
> > > On 4/30/20 9:04 AM, Sowjanya Komatineni wrote:
> > > > 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)
> > > > > > > > +{
> > > > > > > > +ÂÂÂ struct tegra_vi_channel *chan = data;
> > > > > > > > +ÂÂÂ struct tegra_channel_buffer *buf;
> > > > > > > > +
> > > > > > > > +ÂÂÂ set_freezable();
> > > > > > > > +
> > > > > > > > +ÂÂÂ while (1) {
> > > > > > > > +ÂÂÂÂÂÂÂ try_to_freeze();
> > > > > > > I guess it won't be great to freeze in the middle of a capture 
> > > > > > > process, so:
> > > > > > > ÂÂÂÂÂÂÂ if (list_empty(&chan->done))
> > > > > > > ÂÂÂÂÂÂÂÂÂÂÂ 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) &&
> > > > > ÂÂÂÂ list_empty(&chan->done))
> > > > > ÂÂÂÂtry_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.
> > > Also if we add check for both lists empty, freeze is not allowed as 
> > > long as streaming is going on and in case of continuous streaming 
> > > freeze will never happen.
> To allow freeze b/w frames (but not in middle of a frame),
>
> for capture_start thread, probably we can do unconditional 
> try_to_freeze()
>
> for capture_finish thread, at end of capture done we can do 
> try_to_freeze() only when done list is empty
My understanding is buffer updates/release should not happen after 
frozen state. So we should let frame capture of outstanding buffer to 
finish before freezing in capture_finish thread.

But for capture_start thread we can unconditionally freeze before 
dequeuing next buffer for capture.

With this when both threads are in frozen state and no buffer 
updates/captures will happen after frozen state.

I think its not required to finish streaming of all frames completely to 
let threads to enter frozen state as streaming can be continuous as well.

> > Hi Dmitry,
> >
> > Will update in v12 to not allow freeze in middle of a frame capture.
> >
> > Can you please confirm on above if you agree to allow freeze to 
> > happen in b/w frame captures?
> >
> > Also as most feedback has been received from you by now, appreciate 
> > if you can provide all in this v11 if you have anything else so we 
> > will not have any new changes after v12.
> >
> > Thanks
> >
> > Sowjanya