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
 ---------------------------------