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authorTakashi Iwai <tiwai@suse.de>2007-09-17 13:08:32 -0400
committerJaroslav Kysela <perex@perex.cz>2007-10-16 10:50:52 -0400
commit3723e2d25151f919e55da98f89a2787802ad5494 (patch)
treedbec4e33ebef38af1e94930d8490fb8ffd9b1e17 /Documentation
parent7a5a27cfaedf8589600b7ae585f3ca42b2d3c78a (diff)
[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 <tiwai@suse.de> Signed-off-by: Jaroslav Kysela <perex@suse.cz>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/sound/alsa/ALSA-Configuration.txt9
-rw-r--r--Documentation/sound/alsa/powersave.txt41
2 files changed, 44 insertions, 6 deletions
diff --git a/Documentation/sound/alsa/ALSA-Configuration.txt b/Documentation/sound/alsa/ALSA-Configuration.txt
index ef330715c6d6..9268925f8e42 100644
--- a/Documentation/sound/alsa/ALSA-Configuration.txt
+++ b/Documentation/sound/alsa/ALSA-Configuration.txt
@@ -770,7 +770,7 @@ Prior to version 0.9.0rc4 options had a 'snd_' prefix. This was removed.
770 codecs (for debugging only) 770 codecs (for debugging only)
771 enable_msi - Enable Message Signaled Interrupt (MSI) (default = off) 771 enable_msi - Enable Message Signaled Interrupt (MSI) (default = off)
772 power_save - Automatic power-saving timtout (in second, 0 = 772 power_save - Automatic power-saving timtout (in second, 0 =
773 disable, default = 10) 773 disable)
774 power_save_controller - Reset HD-audio controller in power-saving mode 774 power_save_controller - Reset HD-audio controller in power-saving mode
775 (default = on) 775 (default = on)
776 776
@@ -1024,11 +1024,8 @@ Prior to version 0.9.0rc4 options had a 'snd_' prefix. This was removed.
1024 subsystem ID (output of "lspci -nv") to ALSA BTS or alsa-devel 1024 subsystem ID (output of "lspci -nv") to ALSA BTS or alsa-devel
1025 ML (see the section "Links and Addresses"). 1025 ML (see the section "Links and Addresses").
1026 1026
1027 When CONFIG_SND_HDA_POWER_SAVE is set, two options, power_save and 1027 power_save and power_save_controller options are for power-saving
1028 power_save_controller become available. power_save specifies the 1028 mode. See powersave.txt for details.
1029 time to turn off the power automatically at idle status. When
1030 power_save_controller is true, the controller is also turned off.
1031 This might result in more obvious click noise at turning on/off.
1032 1029
1033 Note 2: If you get click noises on output, try the module option 1030 Note 2: If you get click noises on output, try the module option
1034 position_fix=1 or 2. position_fix=1 will use the SD_LPIB 1031 position_fix=1 or 2. position_fix=1 will use the SD_LPIB
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 @@
1Notes on Power-Saving Mode
2==========================
3
4AC97 and HD-audio drivers have the automatic power-saving mode.
5This feature is enabled via Kconfig CONFIG_SND_AC97_POWER_SAVE
6and CONFIG_SND_HDA_POWER_SAVE options, respectively.
7
8With the automatic power-saving, the driver turns off the codec power
9appropriately when no operation is required. When no applications use
10the device and/or no analog loopback is set, the power disablement is
11done fully or partially. It'll save a certain power consumption, thus
12good for laptops (even for desktops).
13
14The time-out for automatic power-off can be specified via power_save
15module option of snd-ac97-codec and snd-hda-intel modules. Specify
16the time-out value in seconds. 0 means to disable the automatic
17power-saving. The default value of timeout is given via
18CONFIG_SND_AC97_POWER_SAVE_DEFAULT and
19CONFIG_SND_HDA_POWER_SAVE_DEFAULT Kconfig options. Setting this to 1
20(the minimum value) isn't recommended because many applications try to
21reopen the device frequently. 10 would be a good choice for normal
22operations.
23
24The power_save option is exported as writable. This means you can
25adjust the value via sysfs on the fly. For example, to turn on the
26automatic power-save mode with 10 seconds, write to
27/sys/modules/snd_ac97_codec/parameters/power_save (usually as root):
28
29 # echo 10 > /sys/modules/snd_ac97_codec/parameters/power_save
30
31
32Note that you might hear click noise/pop when changing the power
33state. Also, it often takes certain time to wake up from the
34power-down to the active state. These are often hardly to fix, so
35don't report extra bug reports unless you have a fix patch ;-)
36
37For HD-audio interface, there is another module option,
38power_save_controller. This enables/disables the power-save mode of
39the controller side. Setting this on may reduce a bit more power
40consumption, but might result in longer wake-up time and click noise.
41Try to turn it off when you experience such a thing too often.