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-rw-r--r--Documentation/thinkpad-acpi.txt61
1 files changed, 35 insertions, 26 deletions
diff --git a/Documentation/thinkpad-acpi.txt b/Documentation/thinkpad-acpi.txt
index ec499265dec..a743bfa62b9 100644
--- a/Documentation/thinkpad-acpi.txt
+++ b/Documentation/thinkpad-acpi.txt
@@ -923,19 +923,26 @@ sysfs backlight device "thinkpad_screen"
This feature allows software control of the LCD brightness on ThinkPad
models which don't have a hardware brightness slider.
-It has some limitations: the LCD backlight cannot be actually turned on or off
-by this interface, and in many ThinkPad models, the "dim while on battery"
-functionality will be enabled by the BIOS when this interface is used, and
-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.
+It has some limitations: the LCD backlight cannot be actually turned on or
+off by this interface, and in many ThinkPad models, the "dim while on
+battery" functionality will be enabled by the BIOS when this interface is
+used, and cannot be controlled.
+
+On IBM (and some of the earlier Lenovo) ThinkPads, the backlight control
+has eight brightness levels, ranging from 0 to 7. Some of the levels
+may not be distinct. Later Lenovo models that implement the ACPI
+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
+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.
+
+When display backlight brightness controls are available through the
+standard ACPI interface, it is best to use it instead of this direct
+ThinkPad-specific interface.
Procfs notes:
@@ -947,11 +954,11 @@ Procfs notes:
Sysfs notes:
-The interface is implemented through the backlight sysfs class, which is poorly
-documented at this time.
+The interface is implemented through the backlight sysfs class, which is
+poorly documented at this time.
-Locate the thinkpad_screen device under /sys/class/backlight, and inside it
-there will be the following attributes:
+Locate the thinkpad_screen device under /sys/class/backlight, and inside
+it there will be the following attributes:
max_brightness:
Reads the maximum brightness the hardware can be set to.
@@ -961,17 +968,19 @@ there will be the following attributes:
Reads what brightness the screen is set to at this instant.
brightness:
- Writes request the driver to change brightness to the given
- value. Reads will tell you what brightness the driver is trying
- to set the display to when "power" is set to zero and the display
- has not been dimmed by a kernel power management event.
+ Writes request the driver to change brightness to the
+ given value. Reads will tell you what brightness the
+ driver is trying to set the display to when "power" is set
+ to zero and the display has not been dimmed by a kernel
+ power management event.
power:
- power management mode, where 0 is "display on", and 1 to 3 will
- dim the display backlight to brightness level 0 because
- thinkpad-acpi cannot really turn the backlight off. Kernel
- power management events can temporarily increase the current
- power management level, i.e. they can dim the display.
+ power management mode, where 0 is "display on", and 1 to 3
+ will dim the display backlight to brightness level 0
+ because thinkpad-acpi cannot really turn the backlight
+ off. Kernel power management events can temporarily
+ increase the current power management level, i.e. they can
+ dim the display.
Volume control -- /proc/acpi/ibm/volume