Based on kernel version 3.15.4. Page generated on 2014-07-07 09:04 EST.
1 Notes on Power-Saving Mode 2 ========================== 3 4 AC97 and HD-audio drivers have the automatic power-saving mode. 5 This feature is enabled via Kconfig CONFIG_SND_AC97_POWER_SAVE 6 and CONFIG_SND_HDA_POWER_SAVE options, respectively. 7 8 With the automatic power-saving, the driver turns off the codec power 9 appropriately when no operation is required. When no applications use 10 the device and/or no analog loopback is set, the power disablement is 11 done fully or partially. It'll save a certain power consumption, thus 12 good for laptops (even for desktops). 13 14 The time-out for automatic power-off can be specified via power_save 15 module option of snd-ac97-codec and snd-hda-intel modules. Specify 16 the time-out value in seconds. 0 means to disable the automatic 17 power-saving. The default value of timeout is given via 18 CONFIG_SND_AC97_POWER_SAVE_DEFAULT and 19 CONFIG_SND_HDA_POWER_SAVE_DEFAULT Kconfig options. Setting this to 1 20 (the minimum value) isn't recommended because many applications try to 21 reopen the device frequently. 10 would be a good choice for normal 22 operations. 23 24 The power_save option is exported as writable. This means you can 25 adjust the value via sysfs on the fly. For example, to turn on the 26 automatic power-save mode with 10 seconds, write to 27 /sys/modules/snd_ac97_codec/parameters/power_save (usually as root): 28 29 # echo 10 > /sys/modules/snd_ac97_codec/parameters/power_save 30 31 32 Note that you might hear click noise/pop when changing the power 33 state. Also, it often takes certain time to wake up from the 34 power-down to the active state. These are often hardly to fix, so 35 don't report extra bug reports unless you have a fix patch ;-) 36 37 For HD-audio interface, there is another module option, 38 power_save_controller. This enables/disables the power-save mode of 39 the controller side. Setting this on may reduce a bit more power 40 consumption, but might result in longer wake-up time and click noise. 41 Try to turn it off when you experience such a thing too often.