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