[alsa-devel] [PATCH 14/31] HDA patch_via.c: Add Jack detect feature for VT1708.

[Takashi Iwai]

At Tue, 6 Oct 2009 23:27:35 +0800,
Li Bo wrote:
> 
> On Tue, Oct 6, 2009 at 8:38 PM, Takashi Iwai <tiwai at suse.de> wrote:
> > At Tue, 6 Oct 2009 14:17:40 +0200,
> > Harald Welte wrote:
> >>
> >> Hi all,
> >>
> >> On Tue, Oct 06, 2009 at 08:01:40AM +0200, Takashi Iwai wrote:
> >>
> >> > > As you describe, we implement it with self-reschedule workqueue, acting
> >> > > like a timer.
> >> > > Is there some advice to implement timer-like task, I tested  with timer and
> >> > > it will crash the driver.
> >> >
> >> > Right, you can't call it in a softirq.
> >> >
> >> > A few problems, however:
> >> > - present variable should be in struct via_spec, instead of a static
> >> >   variable in update_hp_jack_state().
> >>
> >> I agree
> >> > - This mechanism is unconditionally invoked on VT1708 although, in
> >> >   theory, you can have a hardware that doesn't need HP jack detection
> >>
> >> Yes, Logan/Li/Lydia: If we generate this kind of workaround with a timer,
> >> it should only be used on those particular chips that absolutely need it.
> >
> > As far as I see, the code is only for VT1708, so it's already specific
> > to the codec chip.  But, even with this chip, you might have a pin
> > configuration that doesn't need the HP jack detection.
> >
> 
> Yes, it's only for VT1708, and HP exists on most cases, and so HP jack detection
> are needed.
> And present will put into via_spec.

If it's restricted only during the opened (better running) PCM stream,
it's not too bad.  But, it'd be even better to check the availability
of HP jack.


> >> > - Waking up each 100ms for the *whole* time is really bad regarding
> >> >   the power-saving; can't it be optimized?
> >>
> >> I would personally actually suggest to simply not support headphone plug events
> >> in case you are using such a [buggy?] chipset that does not support them.
> >>
> >> I mean, what do you gain from that event? It's not something super-important.
> >>
> >> waking up unconditionally every 100ms is really a too high burden on the
> >> battery life.
> >>
> >> Another option might be to make it a module load time parameter, so people
> >> can choose if they actually want to pay the high power/batyery price for this
> >> small feature.
> >
> > Yes.
> >
> > Basically, if we can drop the analog-loopback feature, the HP jack
> > probing can be simplified very much.  The probing is needed only when
> > the PCM is opened/prepared and running.  It can be implemented in a
> > similar way for the volume-update procedure at PCM trigger.
> > And, during PCM running, (relatively) high-frequent polling isn't so
> > critical.
> >
> >
> > thanks,
> >
> > Takashi
> >
> 
> I know that jack detect on VT1708 that do not support unsolicited
> response is weird, but
>  it's for customer request (and so are some other patches:), we just
> have to do something.
> 
> I think it's good in open/close callback, I'll update.
> 
> About self-reschedule workqueue, maybe there are some other choices,
> or should we keep
> using it?

A delayed workqueue is OK.  But, it should check some flag before
rescheduling itself.  Also, don't forget about suspend/resume.


thanks,

Takashi