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Diffstat (limited to 'Documentation/thinkpad-acpi.txt')
| -rw-r--r-- | Documentation/thinkpad-acpi.txt | 35 |
1 files changed, 21 insertions, 14 deletions
diff --git a/Documentation/thinkpad-acpi.txt b/Documentation/thinkpad-acpi.txt index 7a06a27ee37b..bd00d14538c6 100644 --- a/Documentation/thinkpad-acpi.txt +++ b/Documentation/thinkpad-acpi.txt @@ -464,27 +464,34 @@ CMOS control procfs: /proc/acpi/ibm/cmos sysfs device attribute: cmos_command -This feature is used internally by the ACPI firmware to control the -ThinkLight on most newer ThinkPad models. It may also control LCD -brightness, sounds volume and more, but only on some models. +This feature is mostly used internally by the ACPI firmware to keep the legacy +CMOS NVRAM bits in sync with the current machine state, and to record this +state so that the ThinkPad will retain such settings across reboots. + +Some of these commands actually perform actions in some ThinkPad models, but +this is expected to disappear more and more in newer models. As an example, in +a T43 and in a X40, commands 12 and 13 still control the ThinkLight state for +real, but commands 0 to 2 don't control the mixer anymore (they have been +phased out) and just update the NVRAM. The range of valid cmos command numbers is 0 to 21, but not all have an effect and the behavior varies from model to model. Here is the behavior on the X40 (tpb is the ThinkPad Buttons utility): - 0 - no effect but tpb reports "Volume down" - 1 - no effect but tpb reports "Volume up" - 2 - no effect but tpb reports "Mute on" - 3 - simulate pressing the "Access IBM" button - 4 - LCD brightness up - 5 - LCD brightness down - 11 - toggle screen expansion - 12 - ThinkLight on - 13 - ThinkLight off - 14 - no effect but tpb reports ThinkLight status change + 0 - Related to "Volume down" key press + 1 - Related to "Volume up" key press + 2 - Related to "Mute on" key press + 3 - Related to "Access IBM" key press + 4 - Related to "LCD brightness up" key pess + 5 - Related to "LCD brightness down" key press + 11 - Related to "toggle screen expansion" key press/function + 12 - Related to "ThinkLight on" + 13 - Related to "ThinkLight off" + 14 - Related to "ThinkLight" key press (toggle thinklight) The cmos command interface is prone to firmware split-brain problems, as -in newer ThinkPads it is just a compatibility layer. +in newer ThinkPads it is just a compatibility layer. Do not use it, it is +exported just as a debug tool. LED control -- /proc/acpi/ibm/led --------------------------------- |