path: root/Documentation/sound/alsa/powersave.txt
diff options
authorLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-16 10:13:38 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-16 10:13:38 -0700
commitfc8a327db6c46de783b1a4276d846841b9abc24c (patch)
treebee512c142cccea93511debd98ef954581693727 /Documentation/sound/alsa/powersave.txt
parent92d15c2ccbb3e31a3fc71ad28fdb55e1319383c0 (diff)
parent24837e6f249a2c83667552e6871c1543b4a6b934 (diff)
Merge branch 'linus' of master.kernel.org:/pub/scm/linux/kernel/git/perex/alsa
* 'linus' of master.kernel.org:/pub/scm/linux/kernel/git/perex/alsa: (264 commits) [ALSA] version 1.0.15 [ALSA] Fix thinko in cs4231 mce down check [ALSA] sun-cs4231: improved waiting after MCE down [ALSA] sun-cs4231: use cs4231-regs.h [ALSA] This simplifies and fixes waiting loops of the mce_down() [ALSA] This patch adds support for a wavetable chip on [ALSA] This patch removes open_mutex from the ad1848-lib as [ALSA] fix bootup crash in snd_gus_interrupt() [ALSA] hda-codec - Fix SKU ID function for realtek codecs [ALSA] Support ASUS P701 eeepc [0x1043 0x82a1] support [ALSA] hda-codec - Add array terminator for dmic in STAC codec [ALSA] hdsp - Fix zero division [ALSA] usb-audio - Fix double comment [ALSA] hda-codec - Fix STAC922x volume knob control [ALSA] Changed Jaroslav Kysela's e-mail from perex@suse.cz to perex@perex.cz [ALSA] hda-codec - Fix for Fujitsu Lifebook C1410 [ALSA] mpu-401: remove MPU401_INFO_UART_ONLY flag [ALSA] mpu-401: do not require an ACK byte for the ENTER_UART command [ALSA] via82xx - Add DXS quirk for Shuttle AK31v2 [ALSA] hda-codec - Fix input_mux numbers for vaio stac92xx ...
Diffstat (limited to 'Documentation/sound/alsa/powersave.txt')
1 files changed, 41 insertions, 0 deletions
diff --git a/Documentation/sound/alsa/powersave.txt b/Documentation/sound/alsa/powersave.txt
new file mode 100644
index 000000000000..9657e8099228
--- /dev/null
+++ b/Documentation/sound/alsa/powersave.txt
@@ -0,0 +1,41 @@
+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_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
+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.