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thinkpad-acpi: update volume subdriver documentation 

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>
This commit is contained in:
Henrique de Moraes Holschuh 2009-12-26 22:52:16 -02:00 committed by Len Brown
parent ff850c339a
commit 169220f88f
1 changed files with 50 additions and 8 deletions
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58
Documentation/laptops/thinkpad-acpi.txt
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@ -1092,8 +1092,8 @@ WARNING:
its level up and down at every change.
Volume control
--------------
Volume control (Console Audio control)
--------------------------------------
procfs: /proc/acpi/ibm/volume
ALSA: "ThinkPad Console Audio Control", default ID: "ThinkPadEC"
@ -1110,9 +1110,53 @@ the desktop environment to just provide on-screen-display feedback.
Software volume control should be done only in the main AC97/HDA
mixer.
This feature allows volume control on ThinkPad models with a digital
volume knob (when available, not all models have it), as well as
mute/unmute control. The available commands are:
About the ThinkPad Console Audio control:
ThinkPads have a built-in amplifier and muting circuit that drives the
console headphone and speakers. This circuit is after the main AC97
or HDA mixer in the audio path, and under exclusive control of the
firmware.
ThinkPads have three special hotkeys to interact with the console
audio control: volume up, volume down and mute.
It is worth noting that the normal way the mute function works (on
ThinkPads that do not have a "mute LED") is:
1. Press mute to mute. It will *always* mute, you can press it as
many times as you want, and the sound will remain mute.
2. Press either volume key to unmute the ThinkPad (it will _not_
change the volume, it will just unmute).
This is a very superior design when compared to the cheap software-only
mute-toggle solution found on normal consumer laptops: you can be
absolutely sure the ThinkPad will not make noise if you press the mute
button, no matter the previous state.
The IBM ThinkPads, and the earlier Lenovo ThinkPads have variable-gain
amplifiers driving the speakers and headphone output, and the firmware
also handles volume control for the headphone and speakers on these
ThinkPads without any help from the operating system (this volume
control stage exists after the main AC97 or HDA mixer in the audio
path).
The newer Lenovo models only have firmware mute control, and depend on
the main HDA mixer to do volume control (which is done by the operating
system). In this case, the volume keys are filtered out for unmute
key press (there are some firmware bugs in this area) and delivered as
normal key presses to the operating system (thinkpad-acpi is not
involved).
The ThinkPad-ACPI volume control:
The preferred way to interact with the Console Audio control is the
ALSA interface.
The legacy procfs interface allows one to read the current state,
and if volume control is enabled, accepts the following commands:
echo up >/proc/acpi/ibm/volume
echo down >/proc/acpi/ibm/volume
@ -1121,12 +1165,10 @@ mute/unmute control. The available commands are:
echo 'level <level>' >/proc/acpi/ibm/volume
The <level> number range is 0 to 14 although not all of them may be
distinct. The unmute the volume after the mute command, use either the
distinct. To unmute the volume after the mute command, use either the
up or down command (the level command will not unmute the volume), or
the unmute command.
The current volume level and mute state is shown in the file.
You can use the volume_capabilities parameter to tell the driver
whether your thinkpad has volume control or mute-only control:
volume_capabilities=1 for mixers with mute and volume control,