1 files changed, 6 insertions, 0 deletions

diff --git a/Documentation/thinkpad-acpi.txt b/Documentation/thinkpad-acpi.txt
index c670363cf5a4..c145bcce2339 100644
--- a/Documentation/thinkpad-acpi.txt
+++ b/Documentation/thinkpad-acpi.txt
@@ -860,6 +860,12 @@ cannot be controlled.
 The backlight control has eight levels, ranging from 0 to 7.  Some of the
 levels may not be distinct.
 
+There are two interfaces to the firmware for brightness control, EC and CMOS.
+To select which one should be used, use the brightness_mode module parameter:
+brightness_mode=1 selects EC mode, brightness_mode=2 selects CMOS mode,
+brightness_mode=3 selects both EC and CMOS.  The driver tries to autodetect
+which interface to use.
+
 Procfs notes:
 
         The available commands are: