FreeBSD/Linux Kernel Cross Reference
sys/contrib/device-tree/Bindings/power/reset/gpio-restart.txt

     Drive a GPIO line that can be used to restart the system from a restart
     handler.
     
     This binding supports level and edge triggered reset.  At driver load
     time, the driver will request the given gpio line and install a restart
     handler. If the optional properties 'open-source' is not found, the GPIO line
     will be driven in the inactive state.  Otherwise its not driven until
     the restart is initiated.
     
    When the system is restarted, the restart handler will be invoked in
    priority order.  The gpio is configured as an output, and driven active,
    triggering a level triggered reset condition. This will also cause an
    inactive->active edge condition, triggering positive edge triggered
    reset. After a delay specified by active-delay, the GPIO is set to
    inactive, thus causing an active->inactive edge, triggering negative edge
    triggered reset. After a delay specified by inactive-delay, the GPIO
    is driven active again.  After a delay specified by wait-delay, the
    restart handler completes allowing other restart handlers to be attempted.
    
    Required properties:
    - compatible : should be "gpio-restart".
    - gpios : The GPIO to set high/low, see "gpios property" in
      Documentation/devicetree/bindings/gpio/gpio.txt. If the pin should be
      low to reset the board set it to "Active Low", otherwise set
      gpio to "Active High".
    
    Optional properties:
    - open-source : Treat the GPIO as being open source and defer driving
      it to when the restart is initiated.  If this optional property is not
      specified, the GPIO is initialized as an output in its inactive state.
    - priority : A priority ranging from 0 to 255 (default 128) according to
      the following guidelines:
            0:      Restart handler of last resort, with limited restart
                    capabilities
            128:    Default restart handler; use if no other restart handler is
                    expected to be available, and/or if restart functionality is
                    sufficient to restart the entire system
            255:    Highest priority restart handler, will preempt all other
                    restart handlers
    - active-delay: Delay (default 100) to wait after driving gpio active [ms]
    - inactive-delay: Delay (default 100) to wait after driving gpio inactive [ms]
    - wait-delay: Delay (default 3000) to wait after completing restart
      sequence [ms]
    
    Examples:
    
    gpio-restart {
            compatible = "gpio-restart";
            gpios = <&gpio 4 0>;
            priority = <128>;
            active-delay = <100>;
            inactive-delay = <100>;
            wait-delay = <3000>;
    };

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