ubuntu-linux-kernel/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt

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* 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>;
};