linux/Documentation/devicetree/bindings/leds/common.txt
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   1Common leds properties.
   2
   3Optional properties for child nodes:
   4- label : The label for this LED.  If omitted, the label is
   5  taken from the node name (excluding the unit address).
   6
   7- linux,default-trigger :  This parameter, if present, is a
   8    string defining the trigger assigned to the LED.  Current triggers are:
   9     "backlight" - LED will act as a back-light, controlled by the framebuffer
  10                   system
  11     "default-on" - LED will turn on (but for leds-gpio see "default-state"
  12                    property in Documentation/devicetree/bindings/gpio/led.txt)
  13     "heartbeat" - LED "double" flashes at a load average based rate
  14     "ide-disk" - LED indicates disk activity
  15     "timer" - LED flashes at a fixed, configurable rate
  16
  17Examples:
  18
  19system-status {
  20        label = "Status";
  21        linux,default-trigger = "heartbeat";
  22        ...
  23};
  24