1Notes on Power-Saving Mode 2========================== 3 4AC97 and HD-audio drivers have the automatic power-saving mode. 5This feature is enabled via Kconfig CONFIG_SND_AC97_POWER_SAVE 6and CONFIG_SND_HDA_POWER_SAVE options, respectively. 7 8With the automatic power-saving, the driver turns off the codec power 9appropriately when no operation is required. When no applications use 10the device and/or no analog loopback is set, the power disablement is 11done fully or partially. It'll save a certain power consumption, thus 12good for laptops (even for desktops). 13 14The time-out for automatic power-off can be specified via power_save 15module option of snd-ac97-codec and snd-hda-intel modules. Specify 16the time-out value in seconds. 0 means to disable the automatic 17power-saving. The default value of timeout is given via 18CONFIG_SND_AC97_POWER_SAVE_DEFAULT and 19CONFIG_SND_HDA_POWER_SAVE_DEFAULT Kconfig options. Setting this to 1 20(the minimum value) isn't recommended because many applications try to 21reopen the device frequently. 10 would be a good choice for normal 22operations. 23 24The power_save option is exported as writable. This means you can 25adjust the value via sysfs on the fly. For example, to turn on the 26automatic 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 32Note that you might hear click noise/pop when changing the power 33state. Also, it often takes certain time to wake up from the 34power-down to the active state. These are often hardly to fix, so 35don't report extra bug reports unless you have a fix patch ;-) 36 37For HD-audio interface, there is another module option, 38power_save_controller. This enables/disables the power-save mode of 39the controller side. Setting this on may reduce a bit more power 40consumption, but might result in longer wake-up time and click noise. 41Try to turn it off when you experience such a thing too often. 42