Commit d54b7d7f authored by Henrique de Moraes Holschuh's avatar Henrique de Moraes Holschuh Committed by Len Brown
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ACPI: thinkpad-acpi: update CMOS commands documentation 



The CMOS set of commands is often just used to keep the CMOS NVRAM in sync
with whatever the ACPI BIOS has been doing in modern ThinkPads.  In older
ThinkPads, it actually carried out real actions.  Document this.

Signed-off-by: default avatarHenrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: default avatarLen Brown <len.brown@intel.com>
parent 94b08713

Documentation/thinkpad-acpi.txt

+21 −14
Original line number Diff line number Diff line
@@ -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

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