[alsa-devel] hda-intel and runtime power-management

[Takashi Iwai]

At Wed, 10 Aug 2011 22:34:31 +0300,
Tatulea, Dragos wrote:
> 
> On Mon, Aug 8, 2011 at 9:11 AM, Takashi Iwai <tiwai at suse.de> wrote:
> 
> > At Sun, 7 Aug 2011 20:55:52 +0300,
> > Tatulea, Dragos wrote:
> >
> > > >> >> I'm in the process of enabling pm runtime pm for the hda_intel
> > driver,
> > > >> >> not being sure if this is a sane task :). Noticed that
> > > >> >> CONFIG_SND_HDA_POWER_SAVE disables codecs and chip when they are
> > not
> > > >> >> in use, but the power gain is not noticeable on my hw. On the other
> > > >> >> hand, a full suspend (azx_suspend) does save a few hundred mW's.
> > > >> >> I am aware that this is hw specific, but I would like to take
> > > >> >> advantage of the full suspend. Suspend/resume latency is below
> > jiffy
> > > >> >> resolution.
> > > >> >
> > > >> > Hm, it's strange.  Basically the current power-save does almost
> > > >> > equivalent with the normal suspend/resume, i.e. the codec is
> > > >> > suspended and azx_stop_chip() is called.  Make sure that the
> > > >> > power-saving is really kicked in during your test.
> > > >> >
> > > >> Indeed, I checked and a codec is stuck in a power transition for some
> > reason.
> > > >
> > > > You should check who accessing the device files via fuser, etc.
> > > >
> >
> Yes, there's a non-muted pcm around there that prevents the codec from
> sleeping. I have a patch that checks for all substream states and puts the
> chip to sleep when they are all paused/suspended. Is this a bad idea? It
> could be that resuming the chip takes too long, depending on hw...

The PCM state check would be good.


thanks,

Takashi