[alsa-devel] Restore state around suspend/resume

[Takashi Iwai]

At Sun, 30 Nov 2008 12:54:15 -0800,
Dan Nicholson wrote:
> 
> On Sun, Nov 30, 2008 at 12:27 PM, Takashi Iwai <tiwai at suse.de> wrote:
> > At Sun, 30 Nov 2008 10:38:27 -0800,
> > Dan Nicholson wrote:
> >>
> >> On Sun, Nov 30, 2008 at 10:28 AM, Takashi Iwai <tiwai at suse.de> wrote:
> >> > At Sun, 30 Nov 2008 09:30:37 -0800,
> >> > Dan Nicholson wrote:
> >> >>
> >> >> On Sun, Nov 30, 2008 at 9:22 AM, Takashi Iwai <tiwai at suse.de> wrote:
> >> >> > At Sun, 30 Nov 2008 09:10:32 -0800,
> >> >> > Dan Nicholson wrote:
> >> >> >>
> >> >> >> On Sun, Nov 30, 2008 at 9:06 AM, Takashi Iwai <tiwai at suse.de> wrote:
> >> >> >> > At Sun, 30 Nov 2008 08:22:49 -0800,
> >> >> >> > Dan Nicholson wrote:
> >> >> >> >>
> >> >> >> >> On Sun, Nov 30, 2008 at 1:01 AM, Takashi Iwai <tiwai at suse.de> wrote:
> >> >> >> >> > I don't know who introduced it, but maybe it was a workaround...
> >> >> >> >>
> >> >> >> >> Yeah, I'm sure it was a workaround, but we're trying to get rid of the
> >> >> >> >> unnecessary ones now.
> >> >> >> >
> >> >> >> > Even for drivers without PM support, alsactl alone is useless.
> >> >> >> > So I suggest you to remove it.
> >> >> >>
> >> >> >> I'm sorry, but why useless? It seems that it would be useful to
> >> >> >> restore state from userspace if the driver isn't doing that on its
> >> >> >> own.
> >> >> >
> >> >> > Read alsactl "alone".  Without the combination of module unloading and
> >> >> > reloading, it's useless.
> >> >>
> >> >> So, are you saying that all drivers will maintain their state until
> >> >> they are unloaded?
> >> >
> >> > The drivers supporting PM do it, yes.
> >>
> >> Then, for drivers that don't support PM, won't they lose their state
> >> across suspend? Shouldn't we save and restore it from userspace for
> >> those drivers?
> >
> > They may lose the state.  They need anyway unloading and reloading the
> > driver at suspend/resume.  That's why I wrote alsactl "alone" doesn't
> > help.  It must be always coupled with unloading/reloading if it's
> > really needed.  Putting only alsactl is thus useless and misleading.
> 
> Ah, thank you. Then we can drop the alsactl hook and suggest that
> anyone who has a non-PM-aware sound driver needs to add it to
> SUSPEND_MODULES, which unloads and reloads the driver at suspend time.
> Then, hopefully, udev or modprobe is setup to save/restore the state.

Yes.  Or you can comment out about it, too.
Anyway, a definitely better fix is to support PM in the driver.  So,
please don't put such a workaround in the common pm hook in the first
place, anyway...

Most reasons why PM isn't supported are the lack of test hardware (and
the second place is lack of developers).  If the reporter can help
debugging, it'd be much better than sticking with the ugly
workaround.


thanks,

Takashi
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