[alsa-devel] snd-hda-intel: Power management not enabled until audio is played

[Takashi Iwai]

At Mon, 13 Feb 2012 20:51:26 +0100,
Paul Menzel wrote:
> 
> Am Montag, den 13.02.2012, 15:16 +0100 schrieb Takashi Iwai:
> > At Sat, 11 Feb 2012 10:59:04 +0100,
> > Paul Menzel wrote:
> 
> > > playing with PowerTOP 1.97 I notice that it lists 100 % usage for the
> > > Audio device on several systems [1].
> > > 
> > > I made sure that power management is enabled.
> > > 
> > >         $ grep snd /etc/modprobe.d/*
> > >         …: options snd_hda_intel power_save=1
> > >         $ more /sys/module/snd_hda_intel/parameters/power_save_controller
> > >         Y
> > >         $ more /sys/module/snd_hda_intel/parameters/power_save
> > >         0
> > > 
> > > Since I was on AC power pm-utils seems to reset that parameter to not
> > > save power. :/
> > > 
> > >         $ sudo su
> > >         # echo "1" > /sys/module/snd_hda_intel/parameters/power_save
> > >         # exit
> > > 
> > > But enabling that does not change anything right away. Only after using
> > > the device by playing some audio – `speaker-test` in this case, the
> > > power management seems to kick in.
> > 
> > Right, it's a known issue.
> 
> Should I submit a bug report to track that issue?

No need for that.  It's a missing feature but no bug.

> > You don't have to play actually but just opening/closing a device
> > should suffice.
> 
> Is `touch /dev/dsp` enough? I am thinking about adding that command to
> some start script.

I'm not sure whether "touch" program actually works for a device
file.  Playing a sound like "echo -n | aplay" would work.


Takashi