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