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