powersave.rst 2.0 KB

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