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3723e2d2 TI |
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. |