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Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/laptops/thinkpad-acpi.txt | 58 |
1 files changed, 50 insertions, 8 deletions
diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt index 169091f75e6..75afa1229fd 100644 --- a/Documentation/laptops/thinkpad-acpi.txt +++ b/Documentation/laptops/thinkpad-acpi.txt @@ -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, |