1 ========================== 1 ==========================
2 Notes on Power-Saving Mode 2 Notes on Power-Saving Mode
3 ========================== 3 ==========================
4 4
5 AC97 and HD-audio drivers have the automatic p 5 AC97 and HD-audio drivers have the automatic power-saving mode.
6 This feature is enabled via Kconfig ``CONFIG_S 6 This feature is enabled via Kconfig ``CONFIG_SND_AC97_POWER_SAVE``
7 and ``CONFIG_SND_HDA_POWER_SAVE`` options, res 7 and ``CONFIG_SND_HDA_POWER_SAVE`` options, respectively.
8 8
9 With the automatic power-saving, the driver tu 9 With the automatic power-saving, the driver turns off the codec power
10 appropriately when no operation is required. 10 appropriately when no operation is required. When no applications use
11 the device and/or no analog loopback is set, t 11 the device and/or no analog loopback is set, the power disablement is
12 done fully or partially. It'll save a certain 12 done fully or partially. It'll save a certain power consumption, thus
13 good for laptops (even for desktops). 13 good for laptops (even for desktops).
14 14
15 The time-out for automatic power-off can be sp 15 The time-out for automatic power-off can be specified via ``power_save``
16 module option of snd-ac97-codec and snd-hda-in 16 module option of snd-ac97-codec and snd-hda-intel modules. Specify
17 the time-out value in seconds. 0 means to dis 17 the time-out value in seconds. 0 means to disable the automatic
18 power-saving. The default value of timeout is 18 power-saving. The default value of timeout is given via
19 ``CONFIG_SND_AC97_POWER_SAVE_DEFAULT`` and 19 ``CONFIG_SND_AC97_POWER_SAVE_DEFAULT`` and
20 ``CONFIG_SND_HDA_POWER_SAVE_DEFAULT`` Kconfig 20 ``CONFIG_SND_HDA_POWER_SAVE_DEFAULT`` Kconfig options. Setting this to 1
21 (the minimum value) isn't recommended because 21 (the minimum value) isn't recommended because many applications try to
22 reopen the device frequently. 10 would be a g 22 reopen the device frequently. 10 would be a good choice for normal
23 operations. 23 operations.
24 24
25 The ``power_save`` option is exported as writa 25 The ``power_save`` option is exported as writable. This means you can
26 adjust the value via sysfs on the fly. For ex 26 adjust the value via sysfs on the fly. For example, to turn on the
27 automatic power-save mode with 10 seconds, wri 27 automatic power-save mode with 10 seconds, write to
28 ``/sys/modules/snd_ac97_codec/parameters/power 28 ``/sys/modules/snd_ac97_codec/parameters/power_save`` (usually as root):
29 :: 29 ::
30 30
31 # echo 10 > /sys/modules/snd_ac97_code 31 # echo 10 > /sys/modules/snd_ac97_codec/parameters/power_save
32 32
33 33
34 Note that you might hear click noise/pop when 34 Note that you might hear click noise/pop when changing the power
35 state. Also, it often takes certain time to w 35 state. Also, it often takes certain time to wake up from the
36 power-down to the active state. These are oft 36 power-down to the active state. These are often hardly to fix, so
37 don't report extra bug reports unless you have 37 don't report extra bug reports unless you have a fix patch ;-)
38 38
39 For HD-audio interface, there is another modul 39 For HD-audio interface, there is another module option,
40 power_save_controller. This enables/disables 40 power_save_controller. This enables/disables the power-save mode of
41 the controller side. Setting this on may redu 41 the controller side. Setting this on may reduce a bit more power
42 consumption, but might result in longer wake-u 42 consumption, but might result in longer wake-up time and click noise.
43 Try to turn it off when you experience such a 43 Try to turn it off when you experience such a thing too often.
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