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

[Takashi Iwai]

At Sat, 11 Feb 2012 10:59:04 +0100,
Paul Menzel wrote:
> 
> Dear ALSA folks,
> 
> 
> 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.  You don't have to play actually but just
opening/closing a device should suffice.

The reason is that changing the sysfs parameter file would change only
the variable but doesn't trigger the event by itself.  It's possible
to add some triggering action, but it'd become fairly messy.  So I've 
postponed the implementation, so far.


Takashi