Author: Takashi Iwai <[EMAIL PROTECTED]>
AuthorDate: Mon Sep 17 19:08:32 2007 +0200
Committer: Jaroslav Kysela <[EMAIL PROTECTED]>
CommitDate: Tue Oct 16 16:50:52 2007 +0200
[ALSA] Add description about power-saving mode
Added the description about power-saving mode on AC97 and HD-audio drivers.
Signed-off-by: Takashi Iwai <[EMAIL PROTECTED]>
Signed-off-by: Jaroslav Kysela <[EMAIL PROTECTED]>
Documentation/sound/alsa/ALSA-Configuration.txt | 9 ++---
Documentation/sound/alsa/powersave.txt | 41 +++++++++++++++++++++++
2 files changed, 44 insertions(+), 6 deletions(-)
diff --git a/Documentation/sound/alsa/ALSA-Configuration.txt
index ef33071..9268925 100644
@@ -770,7 +770,7 @@ Prior to version 0.9.0rc4 options had a 'snd_' prefix. This
codecs (for debugging only)
enable_msi - Enable Message Signaled Interrupt (MSI) (default = off)
power_save - Automatic power-saving timtout (in second, 0 =
- disable, default = 10)
power_save_controller - Reset HD-audio controller in power-saving mode
(default = on)
@@ -1024,11 +1024,8 @@ Prior to version 0.9.0rc4 options had a 'snd_' prefix.
This was removed.
subsystem ID (output of "lspci -nv") to ALSA BTS or alsa-devel
ML (see the section "Links and Addresses").
- When CONFIG_SND_HDA_POWER_SAVE is set, two options, power_save and
- power_save_controller become available. power_save specifies the
- time to turn off the power automatically at idle status. When
- power_save_controller is true, the controller is also turned off.
- This might result in more obvious click noise at turning on/off.
+ power_save and power_save_controller options are for power-saving
+ mode. See powersave.txt for details.
Note 2: If you get click noises on output, try the module option
position_fix=1 or 2. position_fix=1 will use the SD_LPIB
diff --git a/Documentation/sound/alsa/powersave.txt
new file mode 100644
@@ -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.
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