watchdog: Add support for minimum time between heartbeats

Some watchdogs require a minimum time between heartbeats.
Examples are the watchdogs in DA9062 and AT91SAM9x.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

Documentation/watchdog/watchdog-kernel-api.txt

@@ -52,6 +52,7 @@ struct watchdog_device {
 	unsigned int timeout;
 	unsigned int min_timeout;
 	unsigned int max_timeout;
+	unsigned int min_hw_heartbeat_ms;
 	unsigned int max_hw_heartbeat_ms;
 	struct notifier_block reboot_nb;
 	struct notifier_block restart_nb;
@@ -81,6 +82,8 @@ It contains following fields:
 * max_timeout: the watchdog timer's maximum timeout value (in seconds),
   as seen from userspace. If set, the maximum configurable value for
   'timeout'. Not used if max_hw_heartbeat_ms is non-zero.
+* min_hw_heartbeat_ms: Minimum time between heartbeats sent to the chip,
+  in milli-seconds.
 * max_hw_heartbeat_ms: Maximum hardware heartbeat, in milli-seconds.
   If set, the infrastructure will send heartbeats to the watchdog driver
   if 'timeout' is larger than max_hw_heartbeat_ms, unless WDOG_ACTIVE

drivers/watchdog/watchdog_dev.c

@@ -64,6 +64,7 @@ struct watchdog_core_data {
 	struct watchdog_device *wdd;
 	struct mutex lock;
 	unsigned long last_keepalive;
+	unsigned long last_hw_keepalive;
 	struct delayed_work work;
 	unsigned long status;		/* Internal status bits */
 #define _WDOG_DEV_OPEN		0	/* Opened ? */
@@ -137,8 +138,19 @@ static inline void watchdog_update_worker(struct watchdog_device *wdd)
 
 static int __watchdog_ping(struct watchdog_device *wdd)
 {
+	struct watchdog_core_data *wd_data = wdd->wd_data;
+	unsigned long earliest_keepalive = wd_data->last_hw_keepalive +
+				msecs_to_jiffies(wdd->min_hw_heartbeat_ms);
 	int err;
 
+	if (time_is_after_jiffies(earliest_keepalive)) {
+		mod_delayed_work(watchdog_wq, &wd_data->work,
+				 earliest_keepalive - jiffies);
+		return 0;
+	}
+
+	wd_data->last_hw_keepalive = jiffies;
+
 	if (wdd->ops->ping)
 		err = wdd->ops->ping(wdd);  /* ping the watchdog */
 	else
@@ -819,6 +831,9 @@ static int watchdog_cdev_register(struct watchdog_device *wdd, dev_t devno)
 		return err;
 	}
 
+	/* Record time of most recent heartbeat as 'just before now'. */
+	wd_data->last_hw_keepalive = jiffies - 1;
+
 	/*
 	 * If the watchdog is running, prevent its driver from being unloaded,
 	 * and schedule an immediate ping.

include/linux/watchdog.h

@@ -65,6 +65,8 @@ struct watchdog_ops {
  * @max_timeout:The watchdog devices maximum timeout value (in seconds)
  *		as configurable from user space. Only relevant if
  *		max_hw_heartbeat_ms is not provided.
+ * @min_hw_heartbeat_ms:
+ *		Minimum time between heartbeats, in milli-seconds.
  * @max_hw_heartbeat_ms:
  *		Hardware limit for maximum timeout, in milli-seconds.
  *		Replaces max_timeout if specified.
@@ -95,6 +97,7 @@ struct watchdog_device {
 	unsigned int timeout;
 	unsigned int min_timeout;
 	unsigned int max_timeout;
+	unsigned int min_hw_heartbeat_ms;
 	unsigned int max_hw_heartbeat_ms;
 	struct notifier_block reboot_nb;
 	struct notifier_block restart_nb;