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-rw-r--r--Documentation/laptops/thinkpad-acpi.txt12
1 files changed, 9 insertions, 3 deletions
diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt
index 25ed43d0a21f..3d7650768bb5 100644
--- a/Documentation/laptops/thinkpad-acpi.txt
+++ b/Documentation/laptops/thinkpad-acpi.txt
@@ -1157,10 +1157,15 @@ display backlight brightness control methods have 16 levels, ranging
from 0 to 15.
There are two interfaces to the firmware for direct brightness control,
-EC and CMOS. To select which one should be used, use the
+EC and UCMS (or 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 auto-detect which interface to use.
+brightness_mode=2 selects UCMS mode, brightness_mode=3 selects EC
+mode with NVRAM backing (so that brightness changes are remembered
+across shutdown/reboot).
+
+The driver tries to select which interface to use from a table of
+defaults for each ThinkPad model. If it makes a wrong choice, please
+report this as a bug, so that we can fix it.
When display backlight brightness controls are available through the
standard ACPI interface, it is best to use it instead of this direct
@@ -1498,6 +1503,7 @@ to enable more than one output class, just add their values.
(bluetooth, WWAN, UWB...)
0x0008 HKEY event interface, hotkeys
0x0010 Fan control
+ 0x0020 Backlight brightness
There is also a kernel build option to enable more debugging
information, which may be necessary to debug driver problems.