Documentation: Add entry for dell-laptop sysfs interface

Add the documentation for the new sysfs interface of dell-laptop
that allows to configure the keyboard illumination on Dell systems.

Signed-off-by: Gabriele Mazzotta <gabriele.mzt@gmail.com>
Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>

diff --git a/Documentation/ABI/testing/sysfs-platform-dell-laptop b/Documentation/ABI/testing/sysfs-platform-dell-laptop
new file mode 100644 (file)
index 0000000..7969443
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+++ b/Documentation/ABI/testing/sysfs-platform-dell-laptop
@@ -0,0 +1,60 @@
+What:          /sys/class/leds/dell::kbd_backlight/als_setting
+Date:          December 2014
+KernelVersion: 3.19
+Contact:       Gabriele Mazzotta <gabriele.mzt@gmail.com>,
+               Pali Rohár <pali.rohar@gmail.com>
+Description:
+               This file allows to control the automatic keyboard
+               illumination mode on some systems that have an ambient
+               light sensor. Write 1 to this file to enable the auto
+               mode, 0 to disable it.
+
+What:          /sys/class/leds/dell::kbd_backlight/start_triggers
+Date:          December 2014
+KernelVersion: 3.19
+Contact:       Gabriele Mazzotta <gabriele.mzt@gmail.com>,
+               Pali Rohár <pali.rohar@gmail.com>
+Description:
+               This file allows to control the input triggers that
+               turn on the keyboard backlight illumination that is
+               disabled because of inactivity.
+               Read the file to see the triggers available. The ones
+               enabled are preceded by '+', those disabled by '-'.
+
+               To enable a trigger, write its name preceded by '+' to
+               this file. To disable a trigger, write its name preceded
+               by '-' instead.
+
+               For example, to enable the keyboard as trigger run:
+                   echo +keyboard > /sys/class/leds/dell::kbd_backlight/start_triggers
+               To disable it:
+                   echo -keyboard > /sys/class/leds/dell::kbd_backlight/start_triggers
+
+               Note that not all the available triggers can be configured.
+
+What:          /sys/class/leds/dell::kbd_backlight/stop_timeout
+Date:          December 2014
+KernelVersion: 3.19
+Contact:       Gabriele Mazzotta <gabriele.mzt@gmail.com>,
+               Pali Rohár <pali.rohar@gmail.com>
+Description:
+               This file allows to specify the interval after which the
+               keyboard illumination is disabled because of inactivity.
+               The timeouts are expressed in seconds, minutes, hours and
+               days, for which the symbols are 's', 'm', 'h' and 'd'
+               respectively.
+
+               To configure the timeout, write to this file a value along
+               with any the above units. If no unit is specified, the value
+               is assumed to be expressed in seconds.
+
+               For example, to set the timeout to 10 minutes run:
+                   echo 10m > /sys/class/leds/dell::kbd_backlight/stop_timeout
+
+               Note that when this file is read, the returned value might be
+               expressed in a different unit than the one used when the timeout
+               was set.
+
+               Also note that only some timeouts are supported and that
+               some systems might fall back to a specific timeout in case
+               an invalid timeout is written to this file.