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authorLinus Torvalds <torvalds@linux-foundation.org>2009-09-23 09:32:11 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-23 09:32:11 -0700
commitc11f6c82581e8be4e1829c677db54e7f55cebece (patch)
tree1a116241b0831ded998aabe800bdc24104cbd826 /Documentation
parent40aba218969914d1b225e742617adb921cf94eae (diff)
parent193a6dec1c0246a80b6d0101e4f351ccf877bcac (diff)
downloadlinux-c11f6c82581e8be4e1829c677db54e7f55cebece.tar.gz
Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6
* 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6: (119 commits)
  ACPI: don't pass handle for fixed hardware notifications
  ACPI: remove null pointer checks in deferred execution path
  ACPI: simplify deferred execution path
  acerhdf: additional BIOS versions
  acerhdf: convert to dev_pm_ops
  acerhdf: fix fan control for AOA150 model
  thermal: add missing Kconfig dependency
  acpi: switch /proc/acpi/{debug_layer,debug_level} to seq_file
  hp-wmi: fix rfkill memory leak on unload
  ACPI: remove unnecessary #ifdef CONFIG_DMI
  ACPI: linux/acpi.h should not include linux/dmi.h
  hwmon driver for ACPI 4.0 power meters
  topstar-laptop: add new driver for hotkeys support on Topstar N01
  thinkpad_acpi: fix rfkill memory leak on unload
  thinkpad-acpi: report brightness events when required
  thinkpad-acpi: don't poll by default any of the reserved hotkeys
  thinkpad-acpi: Fix procfs hotkey reset command
  thinkpad-acpi: deprecate hotkey_bios_mask
  thinkpad-acpi: hotkey poll fixes
  thinkpad-acpi: be more strict when detecting a ThinkPad
  ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/ABI/stable/sysfs-class-backlight36
-rw-r--r--Documentation/ABI/testing/sysfs-class-lcd23
-rw-r--r--Documentation/ABI/testing/sysfs-class-led28
-rw-r--r--Documentation/ABI/testing/sysfs-platform-asus-laptop52
-rw-r--r--Documentation/ABI/testing/sysfs-platform-eeepc-laptop50
-rw-r--r--Documentation/hwmon/acpi_power_meter51
-rw-r--r--Documentation/laptops/asus-laptop.txt258
-rw-r--r--Documentation/laptops/thinkpad-acpi.txt8
-rw-r--r--Documentation/leds-class.txt9
9 files changed, 509 insertions, 6 deletions
diff --git a/Documentation/ABI/stable/sysfs-class-backlight b/Documentation/ABI/stable/sysfs-class-backlight
new file mode 100644
index 000000000000..4d637e1c4ff7
--- /dev/null
+++ b/Documentation/ABI/stable/sysfs-class-backlight
@@ -0,0 +1,36 @@
+What:		/sys/class/backlight/<backlight>/bl_power
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	Richard Purdie <rpurdie@rpsys.net>
+Description:
+		Control BACKLIGHT power, values are FB_BLANK_* from fb.h
+		 - FB_BLANK_UNBLANK (0)   : power on.
+		 - FB_BLANK_POWERDOWN (4) : power off
+Users:		HAL
+
+What:		/sys/class/backlight/<backlight>/brightness
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	Richard Purdie <rpurdie@rpsys.net>
+Description:
+		Control the brightness for this <backlight>. Values
+		are between 0 and max_brightness. This file will also
+		show the brightness level stored in the driver, which
+		may not be the actual brightness (see actual_brightness).
+Users:		HAL
+
+What:		/sys/class/backlight/<backlight>/actual_brightness
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	Richard Purdie <rpurdie@rpsys.net>
+Description:
+		Show the actual brightness by querying the hardware.
+Users:		HAL
+
+What:		/sys/class/backlight/<backlight>/max_brightness
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	Richard Purdie <rpurdie@rpsys.net>
+Description:
+		Maximum brightness for <backlight>.
+Users:		HAL
diff --git a/Documentation/ABI/testing/sysfs-class-lcd b/Documentation/ABI/testing/sysfs-class-lcd
new file mode 100644
index 000000000000..35906bf7aa70
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-lcd
@@ -0,0 +1,23 @@
+What:		/sys/class/lcd/<lcd>/lcd_power
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	Richard Purdie <rpurdie@rpsys.net>
+Description:
+		Control LCD power, values are FB_BLANK_* from fb.h
+		 - FB_BLANK_UNBLANK (0)   : power on.
+		 - FB_BLANK_POWERDOWN (4) : power off
+
+What:		/sys/class/lcd/<lcd>/contrast
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	Richard Purdie <rpurdie@rpsys.net>
+Description:
+		Current contrast of this LCD device. Value is between 0 and
+		/sys/class/lcd/<lcd>/max_contrast.
+
+What:		/sys/class/lcd/<lcd>/max_contrast
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	Richard Purdie <rpurdie@rpsys.net>
+Description:
+		Maximum contrast for this LCD device.
diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
new file mode 100644
index 000000000000..9e4541d71cb6
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-led
@@ -0,0 +1,28 @@
+What:		/sys/class/leds/<led>/brightness
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	Richard Purdie <rpurdie@rpsys.net>
+Description:
+		Set the brightness of the LED. Most LEDs don't
+		have hardware brightness support so will just be turned on for
+		non-zero brightness settings. The value is between 0 and
+		/sys/class/leds/<led>/max_brightness.
+
+What:		/sys/class/leds/<led>/max_brightness
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	Richard Purdie <rpurdie@rpsys.net>
+Description:
+		Maximum brightness level for this led, default is 255 (LED_FULL).
+
+What:		/sys/class/leds/<led>/trigger
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	Richard Purdie <rpurdie@rpsys.net>
+Description:
+		Set the trigger for this LED. A trigger is a kernel based source
+		of led events.
+		You can change triggers in a similar manner to the way an IO
+		scheduler is chosen. Trigger specific parameters can appear in
+		/sys/class/leds/<led> once a given trigger is selected.
+
diff --git a/Documentation/ABI/testing/sysfs-platform-asus-laptop b/Documentation/ABI/testing/sysfs-platform-asus-laptop
new file mode 100644
index 000000000000..a1cb660c50cf
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-platform-asus-laptop
@@ -0,0 +1,52 @@
+What:		/sys/devices/platform/asus-laptop/display
+Date:		January 2007
+KernelVersion:	2.6.20
+Contact:	"Corentin Chary" <corentincj@iksaif.net>
+Description:
+		This file allows display switching. The value
+		is composed by 4 bits and defined as follow:
+		4321
+		|||`- LCD
+		||`-- CRT
+		|`--- TV
+		`---- DVI
+		Ex: - 0 (0000b) means no display
+		    - 3 (0011b) CRT+LCD.
+
+What:		/sys/devices/platform/asus-laptop/gps
+Date:		January 2007
+KernelVersion:	2.6.20
+Contact:	"Corentin Chary" <corentincj@iksaif.net>
+Description:
+		Control the gps device. 1 means on, 0 means off.
+Users:		Lapsus
+
+What:		/sys/devices/platform/asus-laptop/ledd
+Date:		January 2007
+KernelVersion:	2.6.20
+Contact:	"Corentin Chary" <corentincj@iksaif.net>
+Description:
+		Some models like the W1N have a LED display that can be
+		used to display several informations.
+		To control the LED display, use the following :
+		    echo 0x0T000DDD > /sys/devices/platform/asus-laptop/
+		where T control the 3 letters display, and DDD the 3 digits display.
+		The DDD table can be found in Documentation/laptops/asus-laptop.txt
+
+What:		/sys/devices/platform/asus-laptop/bluetooth
+Date:		January 2007
+KernelVersion:	2.6.20
+Contact:	"Corentin Chary" <corentincj@iksaif.net>
+Description:
+		Control the bluetooth device. 1 means on, 0 means off.
+		This may control the led, the device or both.
+Users:		Lapsus
+
+What:		/sys/devices/platform/asus-laptop/wlan
+Date:		January 2007
+KernelVersion:	2.6.20
+Contact:	"Corentin Chary" <corentincj@iksaif.net>
+Description:
+		Control the bluetooth device. 1 means on, 0 means off.
+		This may control the led, the device or both.
+Users:		Lapsus
diff --git a/Documentation/ABI/testing/sysfs-platform-eeepc-laptop b/Documentation/ABI/testing/sysfs-platform-eeepc-laptop
new file mode 100644
index 000000000000..7445dfb321b5
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-platform-eeepc-laptop
@@ -0,0 +1,50 @@
+What:		/sys/devices/platform/eeepc-laptop/disp
+Date:		May 2008
+KernelVersion:	2.6.26
+Contact:	"Corentin Chary" <corentincj@iksaif.net>
+Description:
+		This file allows display switching.
+		- 1 = LCD
+		- 2 = CRT
+		- 3 = LCD+CRT
+		If you run X11, you should use xrandr instead.
+
+What:		/sys/devices/platform/eeepc-laptop/camera
+Date:		May 2008
+KernelVersion:	2.6.26
+Contact:	"Corentin Chary" <corentincj@iksaif.net>
+Description:
+		Control the camera. 1 means on, 0 means off.
+
+What:		/sys/devices/platform/eeepc-laptop/cardr
+Date:		May 2008
+KernelVersion:	2.6.26
+Contact:	"Corentin Chary" <corentincj@iksaif.net>
+Description:
+		Control the card reader. 1 means on, 0 means off.
+
+What:		/sys/devices/platform/eeepc-laptop/cpufv
+Date:		Jun 2009
+KernelVersion:	2.6.31
+Contact:	"Corentin Chary" <corentincj@iksaif.net>
+Description:
+		Change CPU clock configuration.
+		On the Eee PC 1000H there are three available clock configuration:
+		    * 0 -> Super Performance Mode
+		    * 1 -> High Performance Mode
+		    * 2 -> Power Saving Mode
+		On Eee PC 701 there is only 2 available clock configurations.
+		Available configuration are listed in available_cpufv file.
+		Reading this file will show the raw hexadecimal value which
+		is defined as follow:
+		| 8 bit | 8 bit |
+		    |       `---- Current mode
+		    `------------ Availables modes
+		For example, 0x301 means: mode 1 selected, 3 available modes.
+
+What:		/sys/devices/platform/eeepc-laptop/available_cpufv
+Date:		Jun 2009
+KernelVersion:	2.6.31
+Contact:	"Corentin Chary" <corentincj@iksaif.net>
+Description:
+		List available cpufv modes.
diff --git a/Documentation/hwmon/acpi_power_meter b/Documentation/hwmon/acpi_power_meter
new file mode 100644
index 000000000000..c80399a00c50
--- /dev/null
+++ b/Documentation/hwmon/acpi_power_meter
@@ -0,0 +1,51 @@
+Kernel driver power_meter
+=========================
+
+This driver talks to ACPI 4.0 power meters.
+
+Supported systems:
+  * Any recent system with ACPI 4.0.
+    Prefix: 'power_meter'
+    Datasheet: http://acpi.info/, section 10.4.
+
+Author: Darrick J. Wong
+
+Description
+-----------
+
+This driver implements sensor reading support for the power meters exposed in
+the ACPI 4.0 spec (Chapter 10.4).  These devices have a simple set of
+features--a power meter that returns average power use over a configurable
+interval, an optional capping mechanism, and a couple of trip points.  The
+sysfs interface conforms with the specification outlined in the "Power" section
+of Documentation/hwmon/sysfs-interface.
+
+Special Features
+----------------
+
+The power[1-*]_is_battery knob indicates if the power supply is a battery.
+Both power[1-*]_average_{min,max} must be set before the trip points will work.
+When both of them are set, an ACPI event will be broadcast on the ACPI netlink
+socket and a poll notification will be sent to the appropriate
+power[1-*]_average sysfs file.
+
+The power[1-*]_{model_number, serial_number, oem_info} fields display arbitrary
+strings that ACPI provides with the meter.  The measures/ directory contains
+symlinks to the devices that this meter measures.
+
+Some computers have the ability to enforce a power cap in hardware.  If this is
+the case, the power[1-*]_cap and related sysfs files will appear.  When the
+average power consumption exceeds the cap, an ACPI event will be broadcast on
+the netlink event socket and a poll notification will be sent to the
+appropriate power[1-*]_alarm file to indicate that capping has begun, and the
+hardware has taken action to reduce power consumption.  Most likely this will
+result in reduced performance.
+
+There are a few other ACPI notifications that can be sent by the firmware.  In
+all cases the ACPI event will be broadcast on the ACPI netlink event socket as
+well as sent as a poll notification to a sysfs file.  The events are as
+follows:
+
+power[1-*]_cap will be notified if the firmware changes the power cap.
+power[1-*]_interval will be notified if the firmware changes the averaging
+interval.
diff --git a/Documentation/laptops/asus-laptop.txt b/Documentation/laptops/asus-laptop.txt
new file mode 100644
index 000000000000..c1c5be84e4b1
--- /dev/null
+++ b/Documentation/laptops/asus-laptop.txt
@@ -0,0 +1,258 @@
+Asus Laptop Extras
+
+Version 0.1
+August 6, 2009
+
+Corentin Chary <corentincj@iksaif.net>
+http://acpi4asus.sf.net/
+
+ This driver provides support for extra features of ACPI-compatible ASUS laptops.
+ It may also support some MEDION, JVC or VICTOR laptops (such as MEDION 9675 or
+ VICTOR XP7210 for example). It makes all the extra buttons generate standard
+ ACPI events that go through /proc/acpi/events and input events (like keyboards).
+ On some models adds support for changing the display brightness and output,
+ switching the LCD backlight on and off, and most importantly, allows you to
+ blink those fancy LEDs intended for reporting mail and wireless status.
+
+This driver supercedes the old asus_acpi driver.
+
+Requirements
+------------
+
+  Kernel 2.6.X sources, configured for your computer, with ACPI support.
+  You also need CONFIG_INPUT and CONFIG_ACPI.
+
+Status
+------
+
+ The features currently supported are the following (see below for
+ detailed description):
+
+ - Fn key combinations
+ - Bluetooth enable and disable
+ - Wlan enable and disable
+ - GPS enable and disable
+ - Video output switching
+ - Ambient Light Sensor on and off
+ - LED control
+ - LED Display control
+ - LCD brightness control
+ - LCD on and off
+
+ A compatibility table by model and feature is maintained on the web
+ site, http://acpi4asus.sf.net/.
+
+Usage
+-----
+
+  Try "modprobe asus_acpi". Check your dmesg (simply type dmesg). You should
+  see some lines like this :
+
+      Asus Laptop Extras version 0.42
+        L2D model detected.
+
+  If it is not the output you have on your laptop, send it (and the laptop's
+  DSDT) to me.
+
+  That's all, now, all the events generated by the hotkeys of your laptop
+  should be reported in your /proc/acpi/event entry. You can check with
+  "acpi_listen".
+
+  Hotkeys are also reported as input keys (like keyboards) you can check
+  which key are supported using "xev" under X11.
+
+  You can get informations on the version of your DSDT table by reading the
+  /sys/devices/platform/asus-laptop/infos entry. If you have a question or a
+  bug report to do, please include the output of this entry.
+
+LEDs
+----
+
+  You can modify LEDs be echoing values to /sys/class/leds/asus::*/brightness :
+    echo 1 >  /sys/class/leds/asus::mail/brightness
+  will switch the mail LED on.
+  You can also know if they are on/off by reading their content and use
+  kernel triggers like ide-disk or heartbeat.
+
+Backlight
+---------
+
+  You can control lcd backlight power and brightness with
+  /sys/class/backlight/asus-laptop/. Brightness Values are between 0 and 15.
+
+Wireless devices
+---------------
+
+  You can turn the internal Bluetooth adapter on/off with the bluetooth entry
+  (only on models with Bluetooth). This usually controls the associated LED.
+  Same for Wlan adapter.
+
+Display switching
+-----------------
+
+  Note: the display switching code is currently considered EXPERIMENTAL.
+
+  Switching works for the following models:
+    L3800C
+    A2500H
+    L5800C
+    M5200N
+    W1000N (albeit with some glitches)
+    M6700R
+    A6JC
+    F3J
+
+  Switching doesn't work for the following:
+    M3700N
+    L2X00D (locks the laptop under certain conditions)
+
+  To switch the displays, echo values from 0 to 15 to
+  /sys/devices/platform/asus-laptop/display. The significance of those values
+  is as follows:
+
+  +-------+-----+-----+-----+-----+-----+
+  | Bin   | Val | DVI | TV  | CRT | LCD |
+  +-------+-----+-----+-----+-----+-----+
+  + 0000  +   0 +     +     +     +     +
+  +-------+-----+-----+-----+-----+-----+
+  + 0001  +   1 +     +     +     +  X  +
+  +-------+-----+-----+-----+-----+-----+
+  + 0010  +   2 +     +     +  X  +     +
+  +-------+-----+-----+-----+-----+-----+
+  + 0011  +   3 +     +     +  X  +  X  +
+  +-------+-----+-----+-----+-----+-----+
+  + 0100  +   4 +     +  X  +     +     +
+  +-------+-----+-----+-----+-----+-----+
+  + 0101  +   5 +     +  X  +     + X   +
+  +-------+-----+-----+-----+-----+-----+
+  + 0110  +   6 +     +  X  +  X  +     +
+  +-------+-----+-----+-----+-----+-----+
+  + 0111  +   7 +     +  X  +  X  +  X  +
+  +-------+-----+-----+-----+-----+-----+
+  + 1000  +   8 +  X  +     +     +     +
+  +-------+-----+-----+-----+-----+-----+
+  + 1001  +   9 +  X  +     +     +  X  +
+  +-------+-----+-----+-----+-----+-----+
+  + 1010  +  10 +  X  +     +  X  +     +
+  +-------+-----+-----+-----+-----+-----+
+  + 1011  +  11 +  X  +     +  X  +  X  +
+  +-------+-----+-----+-----+-----+-----+
+  + 1100  +  12 +  X  +  X  +     +     +
+  +-------+-----+-----+-----+-----+-----+
+  + 1101  +  13 +  X  +  X  +     +  X  +
+  +-------+-----+-----+-----+-----+-----+
+  + 1110  +  14 +  X  +  X  +  X  +     +
+  +-------+-----+-----+-----+-----+-----+
+  + 1111  +  15 +  X  +  X  +  X  +  X  +
+  +-------+-----+-----+-----+-----+-----+
+
+  In most cases, the appropriate displays must be plugged in for the above
+  combinations to work. TV-Out may need to be initialized at boot time.
+
+  Debugging:
+  1) Check whether the Fn+F8 key:
+     a) does not lock the laptop (try disabling CONFIG_X86_UP_APIC or boot with
+        noapic / nolapic if it does)
+     b) generates events (0x6n, where n is the value corresponding to the
+        configuration above)
+     c) actually works
+     Record the disp value at every configuration.
+  2) Echo values from 0 to 15 to /sys/devices/platform/asus-laptop/display.
+     Record its value, note any change. If nothing changes, try a broader range,
+     up to 65535.
+  3) Send ANY output (both positive and negative reports are needed, unless your
+     machine is already listed above) to the acpi4asus-user mailing list.
+
+  Note: on some machines (e.g. L3C), after the module has been loaded, only 0x6n
+  events are generated and no actual switching occurs. In such a case, a line
+  like:
+
+    echo $((10#$arg-60)) > /sys/devices/platform/asus-laptop/display
+
+  will usually do the trick ($arg is the 0000006n-like event passed to acpid).
+
+  Note: there is currently no reliable way to read display status on xxN
+  (Centrino) models.
+
+LED display
+-----------
+
+  Some models like the W1N have a LED display that can be used to display
+  several informations.
+
+  LED display works for the following models:
+    W1000N
+    W1J
+
+  To control the LED display, use the following :
+
+    echo 0x0T000DDD > /sys/devices/platform/asus-laptop/
+
+  where T control the 3 letters display, and DDD the 3 digits display,
+  according to the tables below.
+
+         DDD (digits)
+         000 to 999 = display digits
+         AAA        = ---
+         BBB to FFF = turn-off
+
+         T  (type)
+         0 = off
+         1 = dvd
+         2 = vcd
+         3 = mp3
+         4 = cd
+         5 = tv
+         6 = cpu
+         7 = vol
+
+  For example "echo 0x01000001 >/sys/devices/platform/asus-laptop/ledd"
+  would display "DVD001".
+
+Driver options:
+---------------
+
+ Options can be passed to the asus-laptop driver using the standard
+ module argument syntax (<param>=<value> when passing the option to the
+ module or asus-laptop.<param>=<value> on the kernel boot line when
+ asus-laptop is statically linked into the kernel).
+
+	     wapf: WAPF defines the behavior of the Fn+Fx wlan key
+		   The significance of values is yet to be found, but
+		   most of the time:
+		   - 0x0 should do nothing
+		   - 0x1 should allow to control the device with Fn+Fx key.
+		   - 0x4 should send an ACPI event (0x88) while pressing the Fn+Fx key
+		   - 0x5 like 0x1 or 0x4
+
+ The default value is 0x1.
+
+Unsupported models
+------------------
+
+ These models will never be supported by this module, as they use a completely
+ different mechanism to handle LEDs and extra stuff (meaning we have no clue
+ how it works):
+
+ - ASUS A1300 (A1B), A1370D
+ - ASUS L7300G
+ - ASUS L8400
+
+Patches, Errors, Questions:
+--------------------------
+
+ I appreciate any success or failure
+ reports, especially if they add to or correct the compatibility table.
+ Please include the following information in your report:
+
+ - Asus model name
+ - a copy of your ACPI tables, using the "acpidump" utility
+ - a copy of /sys/devices/platform/asus-laptop/infos
+ - which driver features work and which don't
+ - the observed behavior of non-working features
+
+ Any other comments or patches are also more than welcome.
+
+ acpi4asus-user@lists.sourceforge.net
+ http://sourceforge.net/projects/acpi4asus
+
diff --git a/Documentation/laptops/thinkpad-acpi.txt b/Documentation/laptops/thinkpad-acpi.txt
index e2ddcdeb61b6..6d03487ef1c7 100644
--- a/Documentation/laptops/thinkpad-acpi.txt
+++ b/Documentation/laptops/thinkpad-acpi.txt
@@ -219,7 +219,7 @@ The following commands can be written to the /proc/acpi/ibm/hotkey file:
 	echo 0xffffffff > /proc/acpi/ibm/hotkey -- enable all hot keys
 	echo 0 > /proc/acpi/ibm/hotkey -- disable all possible hot keys
 	... any other 8-hex-digit mask ...
-	echo reset > /proc/acpi/ibm/hotkey -- restore the original mask
+	echo reset > /proc/acpi/ibm/hotkey -- restore the recommended mask
 
 The following commands have been deprecated and will cause the kernel
 to log a warning:
@@ -240,9 +240,13 @@ sysfs notes:
 		Returns 0.
 
 	hotkey_bios_mask:
+		DEPRECATED, DON'T USE, WILL BE REMOVED IN THE FUTURE.
+
 		Returns the hot keys mask when thinkpad-acpi was loaded.
 		Upon module unload, the hot keys mask will be restored
-		to this value.
+		to this value.   This is always 0x80c, because those are
+		the hotkeys that were supported by ancient firmware
+		without mask support.
 
 	hotkey_enable:
 		DEPRECATED, WILL BE REMOVED SOON.
diff --git a/Documentation/leds-class.txt b/Documentation/leds-class.txt
index 6399557cdab3..8fd5ca2ae32d 100644
--- a/Documentation/leds-class.txt
+++ b/Documentation/leds-class.txt
@@ -1,3 +1,4 @@
+
 LED handling under Linux
 ========================
 
@@ -5,10 +6,10 @@ If you're reading this and thinking about keyboard leds, these are
 handled by the input subsystem and the led class is *not* needed.
 
 In its simplest form, the LED class just allows control of LEDs from
-userspace. LEDs appear in /sys/class/leds/. The brightness file will
-set the brightness of the LED (taking a value 0-255). Most LEDs don't
-have hardware brightness support so will just be turned on for non-zero
-brightness settings.
+userspace. LEDs appear in /sys/class/leds/. The maximum brightness of the
+LED is defined in max_brightness file. The brightness file will set the brightness
+of the LED (taking a value 0-max_brightness). Most LEDs don't have hardware
+brightness support so will just be turned on for non-zero brightness settings.
 
 The class also introduces the optional concept of an LED trigger. A trigger
 is a kernel based source of led events. Triggers can either be simple or