Am Sonntag, den 12.02.2012, 00:22 +0100 schrieb Paul Menzel: > Am Freitag, den 10.02.2012, 06:08 -0800 schrieb Arjan van de Ven: > > On 2/10/2012 1:07 AM, Paul Menzel wrote: > > > Unfortunately neither `lsof` nor `fuser` returned any process using that > > > device. > > > > > > $ sudo lsof /dev/snd/hwC0D0 > > > $ sudo fuser -v /dev/snd/hwC0D0 > > > > also look for /dev/dsp or similar > > That was also to no avail. > > > >> > or you found a real kernel driver bug ;-) > > > Looks like it. I guess I will contact the ALSA list and asking what this > > > device is about and if they can fix it. > > > > > > Could you answer a last question, please? What is PowerTOP actually > > > checking to figure out the usage. > > > > the codec's directory in sysfs (say > > /sys/devices/pci0000.00/0000:00:1b.0/sound/card0/hwC0D3) has 2 files, > > power_on_acct and power_off_act > > these count time that the codec is on or off respectively. > > powertop calculates a delta of these two over the measurement interval > > (20 seconds), and then since it knows how long it was on and off, > > calculates the percentage. > > Thank you very much for that information. I brought that problem up to > the alsa-devel list [1].
According to Takashi Iwai this is a known missing feature nobody has yet implemented. To get the power management enabled the audio device has to be opened by for example `echo -n | aplay`. Unfortunately I do not have any numbers how much “wasted” power we are talking about here. Thanks, Paul > [1] > http://mailman.alsa-project.org/pipermail/alsa-devel/2012-February/049019.html [2] http://mailman.alsa-project.org/pipermail/alsa-devel/2012-February/049095.html
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