1*48e92b48STakashi Iwai========================== 2*48e92b48STakashi IwaiNotes on Power-Saving Mode 3*48e92b48STakashi Iwai========================== 4*48e92b48STakashi Iwai 5*48e92b48STakashi IwaiAC97 and HD-audio drivers have the automatic power-saving mode. 6*48e92b48STakashi IwaiThis feature is enabled via Kconfig ``CONFIG_SND_AC97_POWER_SAVE`` 7*48e92b48STakashi Iwaiand ``CONFIG_SND_HDA_POWER_SAVE`` options, respectively. 8*48e92b48STakashi Iwai 9*48e92b48STakashi IwaiWith the automatic power-saving, the driver turns off the codec power 10*48e92b48STakashi Iwaiappropriately when no operation is required. When no applications use 11*48e92b48STakashi Iwaithe device and/or no analog loopback is set, the power disablement is 12*48e92b48STakashi Iwaidone fully or partially. It'll save a certain power consumption, thus 13*48e92b48STakashi Iwaigood for laptops (even for desktops). 14*48e92b48STakashi Iwai 15*48e92b48STakashi IwaiThe time-out for automatic power-off can be specified via ``power_save`` 16*48e92b48STakashi Iwaimodule option of snd-ac97-codec and snd-hda-intel modules. Specify 17*48e92b48STakashi Iwaithe time-out value in seconds. 0 means to disable the automatic 18*48e92b48STakashi Iwaipower-saving. The default value of timeout is given via 19*48e92b48STakashi Iwai``CONFIG_SND_AC97_POWER_SAVE_DEFAULT`` and 20*48e92b48STakashi Iwai``CONFIG_SND_HDA_POWER_SAVE_DEFAULT`` Kconfig options. Setting this to 1 21*48e92b48STakashi Iwai(the minimum value) isn't recommended because many applications try to 22*48e92b48STakashi Iwaireopen the device frequently. 10 would be a good choice for normal 23*48e92b48STakashi Iwaioperations. 24*48e92b48STakashi Iwai 25*48e92b48STakashi IwaiThe ``power_save`` option is exported as writable. This means you can 26*48e92b48STakashi Iwaiadjust the value via sysfs on the fly. For example, to turn on the 27*48e92b48STakashi Iwaiautomatic power-save mode with 10 seconds, write to 28*48e92b48STakashi Iwai``/sys/modules/snd_ac97_codec/parameters/power_save`` (usually as root): 29*48e92b48STakashi Iwai:: 30*48e92b48STakashi Iwai 31*48e92b48STakashi Iwai # echo 10 > /sys/modules/snd_ac97_codec/parameters/power_save 32*48e92b48STakashi Iwai 33*48e92b48STakashi Iwai 34*48e92b48STakashi IwaiNote that you might hear click noise/pop when changing the power 35*48e92b48STakashi Iwaistate. Also, it often takes certain time to wake up from the 36*48e92b48STakashi Iwaipower-down to the active state. These are often hardly to fix, so 37*48e92b48STakashi Iwaidon't report extra bug reports unless you have a fix patch ;-) 38*48e92b48STakashi Iwai 39*48e92b48STakashi IwaiFor HD-audio interface, there is another module option, 40*48e92b48STakashi Iwaipower_save_controller. This enables/disables the power-save mode of 41*48e92b48STakashi Iwaithe controller side. Setting this on may reduce a bit more power 42*48e92b48STakashi Iwaiconsumption, but might result in longer wake-up time and click noise. 43*48e92b48STakashi IwaiTry to turn it off when you experience such a thing too often. 44