PM / watchdog: iTCO: stop watchdog during system suspend

If the target sleep state of the system is not an ACPI sleep state
(S1, S2 or S3), the TCO watchdog needs to be stopped during system
suspend, because it may not be possible to ping it any more after
timekeeping has been suspended (suspend-to-idle does that for
one example).

For this reason, provide ->suspend_noirq and ->resume_noirq
callbacks for the iTCO watchdog driver and use them to stop
and restart the watchdog during system suspend and resume,
respectively, if the system is not going to enter an ACPI
sleep state (in which case the watchdog will be stopped
by the platform firmware before the state is entered).

Reported-and-tested-by: Borun Fu <borun.fu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>

drivers/watchdog/iTCO_wdt.c

@@ -51,6 +51,7 @@
 #define DRV_VERSION	"1.11"
 
 /* Includes */
+#include <linux/acpi.h>			/* For ACPI support */
 #include <linux/module.h>		/* For module specific items */
 #include <linux/moduleparam.h>		/* For new moduleparam's */
 #include <linux/types.h>		/* For standard types (like size_t) */
@@ -103,6 +104,8 @@ static struct {		/* this is private data for the iTCO_wdt device */
 	struct platform_device *dev;
 	/* the PCI-device */
 	struct pci_dev *pdev;
+	/* whether or not the watchdog has been suspended */
+	bool suspended;
 } iTCO_wdt_private;
 
 /* module parameters */
@@ -571,12 +574,60 @@ static void iTCO_wdt_shutdown(struct platform_device *dev)
 	iTCO_wdt_stop(NULL);
 }
 
+#ifdef CONFIG_PM_SLEEP
+/*
+ * Suspend-to-idle requires this, because it stops the ticks and timekeeping, so
+ * the watchdog cannot be pinged while in that state.  In ACPI sleep states the
+ * watchdog is stopped by the platform firmware.
+ */
+
+#ifdef CONFIG_ACPI
+static inline bool need_suspend(void)
+{
+	return acpi_target_system_state() == ACPI_STATE_S0;
+}
+#else
+static inline bool need_suspend(void) { return true; }
+#endif
+
+static int iTCO_wdt_suspend_noirq(struct device *dev)
+{
+	int ret = 0;
+
+	iTCO_wdt_private.suspended = false;
+	if (watchdog_active(&iTCO_wdt_watchdog_dev) && need_suspend()) {
+		ret = iTCO_wdt_stop(&iTCO_wdt_watchdog_dev);
+		if (!ret)
+			iTCO_wdt_private.suspended = true;
+	}
+	return ret;
+}
+
+static int iTCO_wdt_resume_noirq(struct device *dev)
+{
+	if (iTCO_wdt_private.suspended)
+		iTCO_wdt_start(&iTCO_wdt_watchdog_dev);
+
+	return 0;
+}
+
+static struct dev_pm_ops iTCO_wdt_pm = {
+	.suspend_noirq = iTCO_wdt_suspend_noirq,
+	.resume_noirq = iTCO_wdt_resume_noirq,
+};
+
+#define ITCO_WDT_PM_OPS	(&iTCO_wdt_pm)
+#else
+#define ITCO_WDT_PM_OPS	NULL
+#endif /* CONFIG_PM_SLEEP */
+
 static struct platform_driver iTCO_wdt_driver = {
 	.probe          = iTCO_wdt_probe,
 	.remove         = iTCO_wdt_remove,
 	.shutdown       = iTCO_wdt_shutdown,
 	.driver         = {
 		.name   = DRV_NAME,
+		.pm     = ITCO_WDT_PM_OPS,
 	},
 };