[pulseaudio-discuss] Soundcard's powersave mode

[Tanu Kaskinen]

On Sun, 2015-10-04 at 20:28 +0200, Mikhail Morfikov wrote:
> In the case of snd_hda_intel kernel module, there's two options called
> power_save and power_save_controller . I've set them to the following
> values:
> 
> # systool -v -m snd_hda_intel | grep power
>     power_save          = "10"
>     power_save_controller= "Y"
>     
> According to archlinux wiki (https://wiki.archlinux.org/index.php/Power_management#Audio),
> the power_save parameter is measured in seconds, and it should idle the
> audio card after 10s.
> 
> The question is how could I know whether this works or not? Is there
> any way to be sure that the powersave mode was activated? I've heard
> that there's could be some "clicking" when the state of the sound
> card changes, but I don't hear anything. Some people reported that the
> volume behaves really strange, but it seems that it works just fine on
> my machine.
> 
> Does the powersave mode in the kernel module is somehow related to the
> following output?
> 
> $ pacmd list-sinks | egrep -i "state|suspend"
>         state: SUSPENDED
>         suspend cause: IDLE
> 
> I noticed that when some app plays audio stream, the state becomes
> RUNNING. When the app stops playing, the state changes to IDLE, and
> about 5s later, it changes to the state that you can see above. This
> behavior is the same no matter what I set in the power_save option
> in the kernel module. I've tested 0, 1 and 10, and actually I didn't
> notice any difference.
> 
> So, is the powersave mode enabled or not?

I'm not familiar with the kenel module, so I can't answer most of your
questions. However, I can tell you that the PulseAudio sink state (IDLE
or SUSPENDED) is not the same thing as the kernel driver's power save
state. Based on your description, the driver enters the power save mode
10 seconds after the PulseAudio sink state has changed to SUSPENDED
(suspending means that PulseAudio closes the alsa device).

-- 
Tanu