dm: Simple Watchdog uclass

This is a simple uclass for Watchdog Timers. It has four operations:
start, restart, reset, stop. Drivers must implement start, restart and
stop operations, while implementing reset is optional: It's default
implementation expires watchdog timer in one clock tick.

Signed-off-by: Maxim Sloyko <maxims@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/dm/uclass-id.h

@@ -84,6 +84,7 @@ enum uclass_id {
 	UCLASS_VIDEO,		/* Video or LCD device */
 	UCLASS_VIDEO_BRIDGE,	/* Video bridge, e.g. DisplayPort to LVDS */
 	UCLASS_VIDEO_CONSOLE,	/* Text console driver for video device */
+	UCLASS_WDT,		/* Watchdot Timer driver */
 
 	UCLASS_COUNT,
 	UCLASS_INVALID = -1,

include/wdt.h

@@ -0,0 +1,107 @@
+/*
+ * Copyright 2017 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef _WDT_H_
+#define _WDT_H_
+
+/*
+ * Implement a simple watchdog uclass. Watchdog is basically a timer that
+ * is used to detect or recover from malfunction. During normal operation
+ * the watchdog would be regularly reset to prevent it from timing out.
+ * If, due to a hardware fault or program error, the computer fails to reset
+ * the watchdog, the timer will elapse and generate a timeout signal.
+ * The timeout signal is used to initiate corrective action or actions,
+ * which typically include placing the system in a safe, known state.
+ */
+
+/*
+ * Start the timer
+ *
+ * @dev: WDT Device
+ * @timeout: Number of ticks before timer expires
+ * @flags: Driver specific flags. This might be used to specify
+ * which action needs to be executed when the timer expires
+ * @return: 0 if OK, -ve on error
+ */
+int wdt_start(struct udevice *dev, u64 timeout, ulong flags);
+
+/*
+ * Stop the timer, thus disabling the Watchdog. Use wdt_start to start it again.
+ *
+ * @dev: WDT Device
+ * @return: 0 if OK, -ve on error
+ */
+int wdt_stop(struct udevice *dev);
+
+/*
+ * Reset the timer, typically restoring the counter to
+ * the value configured by start()
+ *
+ * @dev: WDT Device
+ * @return: 0 if OK, -ve on error
+ */
+int wdt_reset(struct udevice *dev);
+
+/*
+ * Expire the timer, thus executing its action immediately.
+ * This is typically used to reset the board or peripherals.
+ *
+ * @dev: WDT Device
+ * @flags: Driver specific flags
+ * @return 0 if OK -ve on error. If wdt action is system reset,
+ * this function may never return.
+ */
+int wdt_expire_now(struct udevice *dev, ulong flags);
+
+/*
+ * struct wdt_ops - Driver model wdt operations
+ *
+ * The uclass interface is implemented by all wdt devices which use
+ * driver model.
+ */
+struct wdt_ops {
+	/*
+	 * Start the timer
+	 *
+	 * @dev: WDT Device
+	 * @timeout: Number of ticks before the timer expires
+	 * @flags: Driver specific flags. This might be used to specify
+	 * which action needs to be executed when the timer expires
+	 * @return: 0 if OK, -ve on error
+	 */
+	int (*start)(struct udevice *dev, u64 timeout, ulong flags);
+	/*
+	 * Stop the timer
+	 *
+	 * @dev: WDT Device
+	 * @return: 0 if OK, -ve on error
+	 */
+	int (*stop)(struct udevice *dev);
+	/*
+	 * Reset the timer, typically restoring the counter to
+	 * the value configured by start()
+	 *
+	 * @dev: WDT Device
+	 * @return: 0 if OK, -ve on error
+	 */
+	int (*reset)(struct udevice *dev);
+	/*
+	 * Expire the timer, thus executing the action immediately (optional)
+	 *
+	 * If this function is not provided, a default implementation
+	 * will be used, which sets the counter to 1
+	 * and waits forever. This is good enough for system level
+	 * reset, where the function is not expected to return, but might not be
+	 * good enough for other use cases.
+	 *
+	 * @dev: WDT Device
+	 * @flags: Driver specific flags
+	 * @return 0 if OK -ve on error. May not return.
+	 */
+	int (*expire_now)(struct udevice *dev, ulong flags);
+};
+
+#endif  /* _WDT_H_ */