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>

1 files changed, 19 insertions, 0 deletions

diff --git a/Documentation/watchdog/watchdog-kernel-api.txt b/Documentation/watchdog/watchdog-kernel-api.txt
index d8b0d33..dbc6a65 100644
--- a/Documentation/watchdog/watchdog-kernel-api.txt
+++ b/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