[Gta04-owner] Some more mA saved on A4 models

NeilBrown neilb at suse.de
Tue Jan 8 07:04:09 CET 2013

On Wed, 2 Jan 2013 20:56:29 +0100 Radek Polak <psonek2 at seznam.cz> wrote:

> Hi,
> i have played a little with alsamixer and i can get the current in suspend 
> equal to A3 models. I am getting max. 22mA in suspend now and i have even seen 
> 18mA.
> The patch and alsa state is here:
> https://github.com/radekp/qtmoko/commit/84fb56edbeeef54a12ce27d79cbceccbea144a1b
> Please read the commit comment if you have ideas.

Just a bit of background that might be helpful:

The sound subsystem in Linux includes "DAPM" - Dynamic Audio Power Management.
This "knows" how everything is connected and will turn things off when not in

The trick is that a loop-back or side channel can connect a source to a sink
even if the audio device is not open, so DAPM will keep the power turned on.

So to power down the audio it isn't sufficient to just close the audio
devices.  You need to mute enough components that there is no path from a
source to a sink.

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