| ========================== | |
| Notes on Power-Saving Mode | |
| ========================== | |
| AC97 and HD-audio drivers have the automatic power-saving mode. | |
| This feature is enabled via Kconfig ``CONFIG_SND_AC97_POWER_SAVE`` | |
| and ``CONFIG_SND_HDA_POWER_SAVE`` options, respectively. | |
| With the automatic power-saving, the driver turns off the codec power | |
| appropriately when no operation is required. When no applications use | |
| the device and/or no analog loopback is set, the power disablement is | |
| done fully or partially. It'll save a certain power consumption, thus | |
| good for laptops (even for desktops). | |
| The time-out for automatic power-off can be specified via ``power_save`` | |
| module option of snd-ac97-codec and snd-hda-intel modules. Specify | |
| the time-out value in seconds. 0 means to disable the automatic | |
| power-saving. The default value of timeout is given via | |
| ``CONFIG_SND_AC97_POWER_SAVE_DEFAULT`` and | |
| ``CONFIG_SND_HDA_POWER_SAVE_DEFAULT`` Kconfig options. Setting this to 1 | |
| (the minimum value) isn't recommended because many applications try to | |
| reopen the device frequently. 10 would be a good choice for normal | |
| operations. | |
| The ``power_save`` option is exported as writable. This means you can | |
| adjust the value via sysfs on the fly. For example, to turn on the | |
| automatic power-save mode with 10 seconds, write to | |
| ``/sys/modules/snd_ac97_codec/parameters/power_save`` (usually as root): | |
| :: | |
| # echo 10 > /sys/modules/snd_ac97_codec/parameters/power_save | |
| Note that you might hear click noise/pop when changing the power | |
| state. Also, it often takes certain time to wake up from the | |
| power-down to the active state. These are often hardly to fix, so | |
| don't report extra bug reports unless you have a fix patch ;-) | |
| For HD-audio interface, there is another module option, | |
| power_save_controller. This enables/disables the power-save mode of | |
| the controller side. Setting this on may reduce a bit more power | |
| consumption, but might result in longer wake-up time and click noise. | |
| Try to turn it off when you experience such a thing too often. |