| ========================== |
| 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. |