led: document sysfs interface

Also fix Documentation/led-class.txt, the acceptable
range of values for brightness is 0-max_brightness, not 0-255.

Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Len Brown <len.brown@intel.com>

2 files changed, 33 insertions, 4 deletions

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/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