ACPI: thinkpad-acpi: update brightness sysfs interface support
Update the brightness sysfs interface (done through the backlight class) to
be in line with the rest of the thinkpad-acpi driver.
This renames the incorrect, un-obvious, and clash-prone name of "ibm" for
the backlight device to a much more fitting and descriptive
"thinkpad_screen". This is something I wanted to do for quite a while...
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/Documentation/thinkpad-acpi.txt b/Documentation/thinkpad-acpi.txt
index 352e8ae..eab4997 100644
--- a/Documentation/thinkpad-acpi.txt
+++ b/Documentation/thinkpad-acpi.txt
@@ -611,19 +611,59 @@
with this, do send me your results (including some complete dumps with
a description of the conditions when they were taken.)
-LCD brightness control -- /proc/acpi/ibm/brightness
----------------------------------------------------
+LCD brightness control
+----------------------
+
+procfs: /proc/acpi/ibm/brightness
+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. The available
-commands are:
+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.
+
+Procfs notes:
+
+ The available commands are:
echo up >/proc/acpi/ibm/brightness
echo down >/proc/acpi/ibm/brightness
echo 'level <level>' >/proc/acpi/ibm/brightness
-The <level> number range is 0 to 7, although not all of them may be
-distinct. The current brightness level is shown in the file.
+Sysfs notes:
+
+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:
+
+ max_brightness:
+ Reads the maximum brightness the hardware can be set to.
+ The minimum is always zero.
+
+ actual_brightness:
+ 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.
+
+ 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.
+
Volume control -- /proc/acpi/ibm/volume
---------------------------------------