1========================== 2Notes on Power-Saving Mode 3========================== 4 5AC97 and HD-audio drivers have the automatic power-saving mode. 6This feature is enabled via Kconfig ``CONFIG_SND_AC97_POWER_SAVE`` 7and ``CONFIG_SND_HDA_POWER_SAVE`` options, respectively. 8 9With the automatic power-saving, the driver turns off the codec power 10appropriately when no operation is required. When no applications use 11the device and/or no analog loopback is set, the power disablement is 12done fully or partially. It'll save a certain power consumption, thus 13good for laptops (even for desktops). 14 15The time-out for automatic power-off can be specified via ``power_save`` 16module option of snd-ac97-codec and snd-hda-intel modules. Specify 17the time-out value in seconds. 0 means to disable the automatic 18power-saving. The default value of timeout is given via 19``CONFIG_SND_AC97_POWER_SAVE_DEFAULT`` and 20``CONFIG_SND_HDA_POWER_SAVE_DEFAULT`` Kconfig options. Setting this to 1 21(the minimum value) isn't recommended because many applications try to 22reopen the device frequently. 10 would be a good choice for normal 23operations. 24 25The ``power_save`` option is exported as writable. This means you can 26adjust the value via sysfs on the fly. For example, to turn on the 27automatic power-save mode with 10 seconds, write to 28``/sys/modules/snd_ac97_codec/parameters/power_save`` (usually as root): 29:: 30 31 # echo 10 > /sys/modules/snd_ac97_codec/parameters/power_save 32 33 34Note that you might hear click noise/pop when changing the power 35state. Also, it often takes certain time to wake up from the 36power-down to the active state. These are often hardly to fix, so 37don't report extra bug reports unless you have a fix patch ;-) 38 39For HD-audio interface, there is another module option, 40power_save_controller. This enables/disables the power-save mode of 41the controller side. Setting this on may reduce a bit more power 42consumption, but might result in longer wake-up time and click noise. 43Try to turn it off when you experience such a thing too often. 44