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+++ 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: