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authorTakashi Iwai <tiwai@suse.de>2016-11-09 17:54:47 +0300
committerTakashi Iwai <tiwai@suse.de>2016-11-10 20:09:23 +0300
commit48e92b488d3c419e11bbf03c56ceb43399ac1901 (patch)
tree4ade68681f3976ca44656e4138610f45dc0ff91d /Documentation/sound/designs
parentafb8fd3c72a9f00018f7335590c173ce4cc2a43d (diff)
downloadlinux-48e92b488d3c419e11bbf03c56ceb43399ac1901.tar.xz
ALSA: doc: ReSTize powersave document
A simple conversion from a text file. Put into designs subdirectory, although it's mostly relevant with HD-audio. Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'Documentation/sound/designs')
-rw-r--r--Documentation/sound/designs/index.rst1
-rw-r--r--Documentation/sound/designs/powersave.rst43
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diff --git a/Documentation/sound/designs/index.rst b/Documentation/sound/designs/index.rst
index 82d19fe3c380..362e1c23d51f 100644
--- a/Documentation/sound/designs/index.rst
+++ b/Documentation/sound/designs/index.rst
@@ -5,3 +5,4 @@ Designs and Implementations
:maxdepth: 2
procfile
+ powersave
diff --git a/Documentation/sound/designs/powersave.rst b/Documentation/sound/designs/powersave.rst
new file mode 100644
index 000000000000..138157452eb9
--- /dev/null
+++ b/Documentation/sound/designs/powersave.rst
@@ -0,0 +1,43 @@
+==========================
+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.