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

Cc: Richard Purdie <[email protected]>
Signed-off-by: Corentin Chary <[email protected]>
Signed-off-by: Len Brown <[email protected]>
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iksaif authored and lenb committed Aug 28, 2009
1 parent 243ca3e commit 5f634c6
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28 changes: 28 additions & 0 deletions Documentation/ABI/testing/sysfs-class-led
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What: /sys/class/leds/<led>/brightness
Date: March 2006
KernelVersion: 2.6.17
Contact: Richard Purdie <[email protected]>
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 <[email protected]>
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 <[email protected]>
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.

9 changes: 5 additions & 4 deletions Documentation/leds-class.txt
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LED handling under Linux
========================

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
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