[alsa-devel] [RFC PATCH 1/1] ALSA: hda - add a timer to find and suspend idle codecs

[Takashi Iwai]

At Tue, 14 Aug 2012 14:35:56 +0000,
Lin, Mengdong wrote:
> 
> > Is watching the codec power up/down the only purpose?
> > If so, the time for codec power on/off can be already checked in
> > /sys/class/sound/hwC*D*/power_{on|off}_acct files.
> > These are used by powertop, for example.
> 
> Hi Takashi,
> 
> My purpose is to enable runtime power management on HD audio. And I hope to base runtime PM on current power saving implementation.
> 
> The basic idea is:
> For the HD-A controller, runtime PM can be enabled on platforms than can provide acceptable latency on transition from D3 to D0.
> When both power saving and runtime PM are enabled by the user, and if all codec are suspended (in D3), the HD-A controller can also enter low-power state by triggering system runtime suspend. And on user operations or HW wakeup event, HD-A controller will be resumed before codecs.
> 
> In my test, I found the issue described in my patch. Such idle but unsuspended codecs prevent the controller from entering D3 at runtime. So I need a 
> method to detect such idle codecs and suspend them. Even if runtime PM is not enabled, I hope this method can improve current power saving.

Ah I see.  In that case, the better approach is reimplement the
power_save set ops to trigger the power-save evaluation.
As already others mentioned, it's bad to use a timer for such a
purpose.  You know exactly when it must be checked.  It's the time
when power_save option is changed.


Takashi