watchdog: introduce watchdog_dev_suspend/resume

The watchdog drivers often disable wdog clock during suspend and then
enable it again during resume. Nevertheless the ping worker is still
running and can issue low-level ping while the wdog clock is disabled
causing the system hang. To prevent such condition register pm notifier
in the watchdog core which will call watchdog_dev_suspend/resume and
actually cancel ping worker during suspend and restore it back, if
needed, during resume.

Signed-off-by: Grzegorz Jaszczyk <grzegorz.jaszczyk@linaro.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20210618195033.3209598-2-grzegorz.jaszczyk@linaro.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/watchdog_core.c

@@ -34,6 +34,7 @@
 #include <linux/idr.h>		/* For ida_* macros */
 #include <linux/err.h>		/* For IS_ERR macros */
 #include <linux/of.h>		/* For of_get_timeout_sec */
+#include <linux/suspend.h>
 
 #include "watchdog_core.h"	/* For watchdog_dev_register/... */
 
@@ -185,6 +186,33 @@ static int watchdog_restart_notifier(struct notifier_block *nb,
 	return NOTIFY_DONE;
 }
 
+static int watchdog_pm_notifier(struct notifier_block *nb, unsigned long mode,
+				void *data)
+{
+	struct watchdog_device *wdd;
+	int ret = 0;
+
+	wdd = container_of(nb, struct watchdog_device, pm_nb);
+
+	switch (mode) {
+	case PM_HIBERNATION_PREPARE:
+	case PM_RESTORE_PREPARE:
+	case PM_SUSPEND_PREPARE:
+		ret = watchdog_dev_suspend(wdd);
+		break;
+	case PM_POST_HIBERNATION:
+	case PM_POST_RESTORE:
+	case PM_POST_SUSPEND:
+		ret = watchdog_dev_resume(wdd);
+		break;
+	}
+
+	if (ret)
+		return NOTIFY_BAD;
+
+	return NOTIFY_DONE;
+}
+
 /**
  * watchdog_set_restart_priority - Change priority of restart handler
  * @wdd: watchdog device
@@ -292,6 +320,15 @@ static int __watchdog_register_device(struct watchdog_device *wdd)
 				wdd->id, ret);
 	}
 
+	if (test_bit(WDOG_NO_PING_ON_SUSPEND, &wdd->status)) {
+		wdd->pm_nb.notifier_call = watchdog_pm_notifier;
+
+		ret = register_pm_notifier(&wdd->pm_nb);
+		if (ret)
+			pr_warn("watchdog%d: Cannot register pm handler (%d)\n",
+				wdd->id, ret);
+	}
+
 	return 0;
 }
 

drivers/watchdog/watchdog_dev.c

@@ -1228,6 +1228,53 @@ void __exit watchdog_dev_exit(void)
 	kthread_destroy_worker(watchdog_kworker);
 }
 
+int watchdog_dev_suspend(struct watchdog_device *wdd)
+{
+	struct watchdog_core_data *wd_data = wdd->wd_data;
+	int ret = 0;
+
+	if (!wdd->wd_data)
+		return -ENODEV;
+
+	/* ping for the last time before suspend */
+	mutex_lock(&wd_data->lock);
+	if (watchdog_worker_should_ping(wd_data))
+		ret = __watchdog_ping(wd_data->wdd);
+	mutex_unlock(&wd_data->lock);
+
+	if (ret)
+		return ret;
+
+	/*
+	 * make sure that watchdog worker will not kick in when the wdog is
+	 * suspended
+	 */
+	hrtimer_cancel(&wd_data->timer);
+	kthread_cancel_work_sync(&wd_data->work);
+
+	return 0;
+}
+
+int watchdog_dev_resume(struct watchdog_device *wdd)
+{
+	struct watchdog_core_data *wd_data = wdd->wd_data;
+	int ret = 0;
+
+	if (!wdd->wd_data)
+		return -ENODEV;
+
+	/*
+	 * __watchdog_ping will also retrigger hrtimer and therefore restore the
+	 * ping worker if needed.
+	 */
+	mutex_lock(&wd_data->lock);
+	if (watchdog_worker_should_ping(wd_data))
+		ret = __watchdog_ping(wd_data->wdd);
+	mutex_unlock(&wd_data->lock);
+
+	return ret;
+}
+
 module_param(handle_boot_enabled, bool, 0444);
 MODULE_PARM_DESC(handle_boot_enabled,
 	"Watchdog core auto-updates boot enabled watchdogs before userspace takes over (default="

include/linux/watchdog.h

@@ -107,6 +107,7 @@ struct watchdog_device {
 	unsigned int max_hw_heartbeat_ms;
 	struct notifier_block reboot_nb;
 	struct notifier_block restart_nb;
+	struct notifier_block pm_nb;
 	void *driver_data;
 	struct watchdog_core_data *wd_data;
 	unsigned long status;
@@ -116,6 +117,7 @@ struct watchdog_device {
 #define WDOG_STOP_ON_REBOOT	2	/* Should be stopped on reboot */
 #define WDOG_HW_RUNNING		3	/* True if HW watchdog running */
 #define WDOG_STOP_ON_UNREGISTER	4	/* Should be stopped on unregister */
+#define WDOG_NO_PING_ON_SUSPEND	5	/* Ping worker should be stopped on suspend */
 	struct list_head deferred;
 };
 
@@ -156,6 +158,12 @@ static inline void watchdog_stop_on_unregister(struct watchdog_device *wdd)
 	set_bit(WDOG_STOP_ON_UNREGISTER, &wdd->status);
 }
 
+/* Use the following function to stop the wdog ping worker when suspending */
+static inline void watchdog_stop_ping_on_suspend(struct watchdog_device *wdd)
+{
+	set_bit(WDOG_NO_PING_ON_SUSPEND, &wdd->status);
+}
+
 /* Use the following function to check if a timeout value is invalid */
 static inline bool watchdog_timeout_invalid(struct watchdog_device *wdd, unsigned int t)
 {
@@ -209,6 +217,8 @@ extern int watchdog_init_timeout(struct watchdog_device *wdd,
 				  unsigned int timeout_parm, struct device *dev);
 extern int watchdog_register_device(struct watchdog_device *);
 extern void watchdog_unregister_device(struct watchdog_device *);
+int watchdog_dev_suspend(struct watchdog_device *wdd);
+int watchdog_dev_resume(struct watchdog_device *wdd);
 
 int watchdog_set_last_hw_keepalive(struct watchdog_device *, unsigned int);