watchdog: add support for adjusting last known HW keepalive time

Certain watchdogs require the watchdog only to be pinged within a
specific time window, pinging too early or too late cause the watchdog
to fire. In cases where this sort of watchdog has been started before
kernel comes up, we must adjust the watchdog keepalive window to match
the actually running timer, so add a new driver API for this purpose.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200717132958.14304-3-t-kristo@ti.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

Documentation/watchdog/watchdog-kernel-api.rst

@@ -336,3 +336,15 @@ an action is taken by a preconfigured pretimeout governor preassigned to
 the watchdog device. If watchdog pretimeout governor framework is not
 enabled, watchdog_notify_pretimeout() prints a notification message to
 the kernel log buffer.
+
+To set the last known HW keepalive time for a watchdog, the following function
+should be used::
+
+  int watchdog_set_last_hw_keepalive(struct watchdog_device *wdd,
+                                     unsigned int last_ping_ms)
+
+This function must be called immediately after watchdog registration. It
+sets the last known hardware heartbeat to have happened last_ping_ms before
+current time. Calling this is only needed if the watchdog is already running
+when probe is called, and the watchdog can only be pinged after the
+min_hw_heartbeat_ms time has passed from the last ping.

drivers/watchdog/watchdog_dev.c

@@ -1138,6 +1138,36 @@ void watchdog_dev_unregister(struct watchdog_device *wdd)
 	watchdog_cdev_unregister(wdd);
 }
 
+/*
+ *	watchdog_set_last_hw_keepalive: set last HW keepalive time for watchdog
+ *	@wdd: watchdog device
+ *	@last_ping_ms: time since last HW heartbeat
+ *
+ *	Adjusts the last known HW keepalive time for a watchdog timer.
+ *	This is needed if the watchdog is already running when the probe
+ *	function is called, and it can't be pinged immediately. This
+ *	function must be called immediately after watchdog registration,
+ *	and min_hw_heartbeat_ms must be set for this to be useful.
+ */
+int watchdog_set_last_hw_keepalive(struct watchdog_device *wdd,
+				   unsigned int last_ping_ms)
+{
+	struct watchdog_core_data *wd_data;
+	ktime_t now;
+
+	if (!wdd)
+		return -EINVAL;
+
+	wd_data = wdd->wd_data;
+
+	now = ktime_get();
+
+	wd_data->last_hw_keepalive = ktime_sub(now, ms_to_ktime(last_ping_ms));
+
+	return __watchdog_ping(wdd);
+}
+EXPORT_SYMBOL_GPL(watchdog_set_last_hw_keepalive);
+
 /*
  *	watchdog_dev_init: init dev part of watchdog core
  *

include/linux/watchdog.h

@@ -210,6 +210,8 @@ extern int watchdog_init_timeout(struct watchdog_device *wdd,
 extern int watchdog_register_device(struct watchdog_device *);
 extern void watchdog_unregister_device(struct watchdog_device *);
 
+int watchdog_set_last_hw_keepalive(struct watchdog_device *, unsigned int);
+
 /* devres register variant */
 int devm_watchdog_register_device(struct device *dev, struct watchdog_device *);