linux-libre/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt

* GPIO-controlled Watchdog

Required Properties:
- compatible: Should contain "linux,wdt-gpio".
- gpios: From common gpio binding; gpio connection to WDT reset pin.
- hw_algo: The algorithm used by the driver. Should be one of the
  following values:
  - toggle: Either a high-to-low or a low-to-high transition clears
    the WDT counter. The watchdog timer is disabled when GPIO is
    left floating or connected to a three-state buffer.
  - level: Low or high level starts counting WDT timeout,
    the opposite level disables the WDT. Active level is determined
    by the GPIO flags.
- hw_margin_ms: Maximum time to reset watchdog circuit (milliseconds).

Optional Properties:
- always-running: If the watchdog timer cannot be disabled, add this flag to
  have the driver keep toggling the signal without a client. It will only cease
  to toggle the signal when the device is open and the timeout elapsed.

Example:
	watchdog: watchdog {
		/* ADM706 */
		compatible = "linux,wdt-gpio";
		gpios = <&gpio3 9 GPIO_ACTIVE_LOW>;
		hw_algo = "toggle";
		hw_margin_ms = <1600>;
	};