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Takashi Iwai3723e2d2007-09-17 19:08:32 +02001Notes on Power-Saving Mode
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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.