[alsa-devel] Shutdown() vector in ALSA

[Nobin Mathew]

In ubuntu this script mutes all mixer controls.

So there will be no noise (pop/clicks) during shutdown.

since I am writing an ASoC driver, it is better to provide shutdown
vector which will shutdown the system properly.

If SIGTERM is handled properly in the application then this is also
not needed, in this case closing the substream will take care of
proper shutdown (DAPM)

But we need to take care of applications which will not handle SIGTERM properly.

Nobin


On 6/12/07, Takashi Iwai <tiwai at suse.de> wrote:
> At Tue, 12 Jun 2007 10:15:56 +0100,
> James Courtier-Dutton wrote:
> >
> > Takashi Iwai wrote:
> > > At Tue, 12 Jun 2007 14:26:08 +0530,
> > > Nobin Mathew wrote:
> > >> why no ALSA driver has shutdown() vector implemented?
> > >
> > > Because no hardware required it, so far.
> > > The shutdown callback is called only when the device is powered off
> > > while the driver is still active.
> > >
> > >> Is this vector needed to ensure the proper shutdown of the system?
> > >>
> > >> What all needs to be taken care if i want to implement shutdown(),
> > >> except hardware shutdown.
> > >>
> > >>
> > >> struct snd_shutdown_f_ops {
> > >>    struct file_operations f_ops;
> > >>    struct snd_shutdown_f_ops *next;
> > >> };
> > >>
> > >> what this operations means? defined in sound/core/init.c
> > >
> > > This has nothing to do with the driver's shutdown callback.
> > >
> > >
> > >> Is there any need to call these functions?
> > >> snd_power_change_state(card, SNDRV_CTL_POWER_D3hot);
> > >> for (i = 0; i < chip->pcm_devs; i++)
> > >>    snd_pcm_suspend_all(chip->pcm[i]);
> > >
> > > At shutdown, the user processes will be terminated sooner or later.
> > > Thus no freezing is necessary at all.
> > >
> > > What I may be concerned would be a case like the hardware can be
> > > damaged by an accidental turn-off, or, some termination is required
> > > to make the device in a cold state (e.g. otherwise the firwmare won't
> > > be loaded at the next time).
> > > In other cases, usually the init script does necessary things at
> > > shutdown.
> > >
> > >
> > > Takashi
> >
> > It might be nice to implement it, purely to help prevent the click or
> > thump on the speakers at shutdown.
>
> It's already done in init script on SUSE distro since long time
> ago...
>
>
> Takashi
>