watchdog: core: add restart handler support

Many watchdog drivers implement the same code to register a restart
handler. This patch provides a generic way to set such a function.

The patch adds a new restart watchdog operation. If a restart priority
greater than 0 is needed, the driver can call
watchdog_set_restart_priority to set it.
Suggested-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Damien Riegel <damien.riegel@savoirfairelinux.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

Documentation/watchdog/watchdog-kernel-api.txt

@@ -53,6 +53,7 @@ struct watchdog_device {
 	unsigned int timeout;
 	unsigned int min_timeout;
 	unsigned int max_timeout;
+	struct notifier_block restart_nb;
 	void *driver_data;
 	struct mutex lock;
 	unsigned long status;
@@ -75,6 +76,10 @@ It contains following fields:
 * timeout: the watchdog timer's timeout value (in seconds).
 * min_timeout: the watchdog timer's minimum timeout value (in seconds).
 * max_timeout: the watchdog timer's maximum timeout value (in seconds).
+* restart_nb: notifier block that is registered for machine restart, for
+  internal use only. If a watchdog is capable of restarting the machine, it
+  should define ops->restart. Priority can be changed through
+  watchdog_set_restart_priority.
 * bootstatus: status of the device after booting (reported with watchdog
   WDIOF_* status bits).
 * driver_data: a pointer to the drivers private data of a watchdog device.
@@ -100,6 +105,7 @@ struct watchdog_ops {
 	unsigned int (*status)(struct watchdog_device *);
 	int (*set_timeout)(struct watchdog_device *, unsigned int);
 	unsigned int (*get_timeleft)(struct watchdog_device *);
+	int (*restart)(struct watchdog_device *);
 	void (*ref)(struct watchdog_device *);
 	void (*unref)(struct watchdog_device *);
 	long (*ioctl)(struct watchdog_device *, unsigned int, unsigned long);
@@ -164,6 +170,8 @@ they are supported. These optional routines/operations are:
   (Note: the WDIOF_SETTIMEOUT needs to be set in the options field of the
   watchdog's info structure).
 * get_timeleft: this routines returns the time that's left before a reset.
+* restart: this routine restarts the machine. It returns 0 on success or a
+  negative errno code for failure.
 * ref: the operation that calls kref_get on the kref of a dynamically
   allocated watchdog_device struct.
 * unref: the operation that calls kref_put on the kref of a dynamically
@@ -231,3 +239,14 @@ the device tree (if the module timeout parameter is invalid). Best practice is
 to set the default timeout value as timeout value in the watchdog_device and
 then use this function to set the user "preferred" timeout value.
 This routine returns zero on success and a negative errno code for failure.
+
+To change the priority of the restart handler the following helper should be
+used:
+
+void watchdog_set_restart_priority(struct watchdog_device *wdd, int priority);
+
+User should follow the following guidelines for setting the priority:
+* 0: should be called in last resort, has limited restart capabilities
+* 128: default restart handler, use if no other handler is expected to be
+  available, and/or if restart is sufficient to restart the entire system
+* 255: highest priority, will preempt all other restart handlers

drivers/watchdog/watchdog_core.c

@@ -32,6 +32,7 @@
 #include <linux/types.h>	/* For standard types */
 #include <linux/errno.h>	/* For the -ENODEV/... values */
 #include <linux/kernel.h>	/* For printk/panic/... */
+#include <linux/reboot.h>	/* For restart handler */
 #include <linux/watchdog.h>	/* For watchdog specific items */
 #include <linux/init.h>		/* For __init/__exit/... */
 #include <linux/idr.h>		/* For ida_* macros */
@@ -137,6 +138,41 @@ int watchdog_init_timeout(struct watchdog_device *wdd,
 }
 EXPORT_SYMBOL_GPL(watchdog_init_timeout);
 
+static int watchdog_restart_notifier(struct notifier_block *nb,
+				     unsigned long action, void *data)
+{
+	struct watchdog_device *wdd = container_of(nb, struct watchdog_device,
+						   restart_nb);
+
+	int ret;
+
+	ret = wdd->ops->restart(wdd);
+	if (ret)
+		return NOTIFY_BAD;
+
+	return NOTIFY_DONE;
+}
+
+/**
+ * watchdog_set_restart_priority - Change priority of restart handler
+ * @wdd: watchdog device
+ * @priority: priority of the restart handler, should follow these guidelines:
+ *   0:   use watchdog's restart function as last resort, has limited restart
+ *        capabilies
+ *   128: default restart handler, use if no other handler is expected to be
+ *        available and/or if restart is sufficient to restart the entire system
+ *   255: preempt all other handlers
+ *
+ * If a wdd->ops->restart function is provided when watchdog_register_device is
+ * called, it will be registered as a restart handler with the priority given
+ * here.
+ */
+void watchdog_set_restart_priority(struct watchdog_device *wdd, int priority)
+{
+	wdd->restart_nb.priority = priority;
+}
+EXPORT_SYMBOL_GPL(watchdog_set_restart_priority);
+
 static int __watchdog_register_device(struct watchdog_device *wdd)
 {
 	int ret, id = -1, devno;
@@ -202,6 +238,15 @@ static int __watchdog_register_device(struct watchdog_device *wdd)
 		return ret;
 	}
 
+	if (wdd->ops->restart) {
+		wdd->restart_nb.notifier_call = watchdog_restart_notifier;
+
+		ret = register_restart_handler(&wdd->restart_nb);
+		if (ret)
+			dev_warn(wdd->dev, "Cannot register restart handler (%d)\n",
+				 ret);
+	}
+
 	return 0;
 }
 
@@ -238,6 +283,9 @@ static void __watchdog_unregister_device(struct watchdog_device *wdd)
 	if (wdd == NULL)
 		return;
 
+	if (wdd->ops->restart)
+		unregister_restart_handler(&wdd->restart_nb);
+
 	devno = wdd->cdev.dev;
 	ret = watchdog_dev_unregister(wdd);
 	if (ret)

include/linux/watchdog.h

@@ -12,6 +12,7 @@
 #include <linux/bitops.h>
 #include <linux/device.h>
 #include <linux/cdev.h>
+#include <linux/notifier.h>
 #include <uapi/linux/watchdog.h>
 
 struct watchdog_ops;
@@ -26,6 +27,7 @@ struct watchdog_device;
  * @status:	The routine that shows the status of the watchdog device.
  * @set_timeout:The routine for setting the watchdog devices timeout value (in seconds).
  * @get_timeleft:The routine that gets the time left before a reset (in seconds).
+ * @restart:	The routine for restarting the machine.
  * @ref:	The ref operation for dyn. allocated watchdog_device structs
  * @unref:	The unref operation for dyn. allocated watchdog_device structs
  * @ioctl:	The routines that handles extra ioctl calls.
@@ -45,6 +47,7 @@ struct watchdog_ops {
 	unsigned int (*status)(struct watchdog_device *);
 	int (*set_timeout)(struct watchdog_device *, unsigned int);
 	unsigned int (*get_timeleft)(struct watchdog_device *);
+	int (*restart)(struct watchdog_device *);
 	void (*ref)(struct watchdog_device *);
 	void (*unref)(struct watchdog_device *);
 	long (*ioctl)(struct watchdog_device *, unsigned int, unsigned long);
@@ -62,6 +65,7 @@ struct watchdog_ops {
  * @timeout:	The watchdog devices timeout value (in seconds).
  * @min_timeout:The watchdog devices minimum timeout value (in seconds).
  * @max_timeout:The watchdog devices maximum timeout value (in seconds).
+ * @restart_nb:	The notifier block to register a restart function.
  * @driver-data:Pointer to the drivers private data.
  * @lock:	Lock for watchdog core internal use only.
  * @status:	Field that contains the devices internal status bits.
@@ -88,6 +92,7 @@ struct watchdog_device {
 	unsigned int timeout;
 	unsigned int min_timeout;
 	unsigned int max_timeout;
+	struct notifier_block restart_nb;
 	void *driver_data;
 	struct mutex lock;
 	unsigned long status;
@@ -142,6 +147,7 @@ static inline void *watchdog_get_drvdata(struct watchdog_device *wdd)
 }
 
 /* drivers/watchdog/watchdog_core.c */
+void watchdog_set_restart_priority(struct watchdog_device *wdd, int priority);
 extern int watchdog_init_timeout(struct watchdog_device *wdd,
 				  unsigned int timeout_parm, struct device *dev);
 extern int watchdog_register_device(struct watchdog_device *);