diff options
| -rw-r--r-- | Documentation/sound/alsa/ALSA-Configuration.txt | 9 | ||||
| -rw-r--r-- | Documentation/sound/alsa/powersave.txt | 41 |
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. 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) + disable) 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 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_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. |