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Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.

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