[alsa-devel] Shutdown() vector in ALSA

[Takashi Iwai]

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