watchdog: add watchdog pretimeout governor framework

The change adds a simple watchdog pretimeout framework infrastructure,
its purpose is to allow users to select a desired handling of watchdog
pretimeout events, which may be generated by some watchdog devices.

A user selects a default watchdog pretimeout governor during
compilation stage.

Watchdogs with WDIOF_PRETIMEOUT capability now have one more device
attribute in sysfs, pretimeout_governor attribute is intended to display
the selected watchdog pretimeout governor.

The framework has no impact at runtime on watchdog devices with no
WDIOF_PRETIMEOUT capability set.

Signed-off-by: Vladimir Zapolskiy <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Reviewed-by: Wolfram Sang <[e-mail]>
Tested-by: Wolfram Sang <[e-mail]>
Signed-off-by: Guenter Roeck <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>

Documentation/watchdog/watchdog-kernel-api.txt

···
 	const struct attribute_group **groups;
 	const struct watchdog_info *info;
 	const struct watchdog_ops *ops;
+	const struct watchdog_governor *gov;
 	unsigned int bootstatus;
 	unsigned int timeout;
 	unsigned int pretimeout;
···
 * info: a pointer to a watchdog_info structure. This structure gives some
   additional information about the watchdog timer itself. (Like it's unique name)
 * ops: a pointer to the list of watchdog operations that the watchdog supports.
+* gov: a pointer to the assigned watchdog device pretimeout governor or NULL.
 * timeout: the watchdog timer's timeout value (in seconds).
   This is the time after which the system will reboot if user space does
   not send a heartbeat request if WDOG_ACTIVE is set.
···
 * 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
+
+To raise a pretimeout notification, the following function should be used:
+
+void watchdog_notify_pretimeout(struct watchdog_device *wdd)
+
+The function can be called in the interrupt context. If watchdog pretimeout
+governor framework (kbuild CONFIG_WATCHDOG_PRETIMEOUT_GOV symbol) is enabled,
+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.

drivers/watchdog/Kconfig

···
 
 	  Most people will say N.
 
+comment "Watchdog Pretimeout Governors"
+
+config WATCHDOG_PRETIMEOUT_GOV
+	bool "Enable watchdog pretimeout governors"
+	help
+	  The option allows to select watchdog pretimeout governors.
+
 endif # WATCHDOG

drivers/watchdog/Makefile

···
 #
 
 # The WatchDog Timer Driver Core.
-watchdog-objs	+= watchdog_core.o watchdog_dev.o
 obj-$(CONFIG_WATCHDOG_CORE)	+= watchdog.o
+
+watchdog-objs	+= watchdog_core.o watchdog_dev.o
+
+watchdog-$(CONFIG_WATCHDOG_PRETIMEOUT_GOV)	+= watchdog_pretimeout.o
 
 # Only one watchdog can succeed. We probe the ISA/PCI/USB based
 # watchdog-cards first, then the architecture specific watchdog

drivers/watchdog/watchdog_dev.c

···
 #include <linux/uaccess.h>	/* For copy_to_user/put_user/... */
 
 #include "watchdog_core.h"
+#include "watchdog_pretimeout.h"
 
 /*
  * struct watchdog_core_data - watchdog core internal data
···
 }
 static DEVICE_ATTR_RO(state);
 
+static ssize_t pretimeout_governor_show(struct device *dev,
+					struct device_attribute *attr,
+					char *buf)
+{
+	struct watchdog_device *wdd = dev_get_drvdata(dev);
+
+	return watchdog_pretimeout_governor_get(wdd, buf);
+}
+static DEVICE_ATTR_RO(pretimeout_governor);
+
 static umode_t wdt_is_visible(struct kobject *kobj, struct attribute *attr,
 				int n)
 {
···
 		mode = 0;
 	else if (attr == &dev_attr_pretimeout.attr &&
 		 !(wdd->info->options & WDIOF_PRETIMEOUT))
+		mode = 0;
+	else if (attr == &dev_attr_pretimeout_governor.attr &&
+		 (!(wdd->info->options & WDIOF_PRETIMEOUT) ||
+		  !IS_ENABLED(CONFIG_WATCHDOG_PRETIMEOUT_GOV)))
 		mode = 0;
 
 	return mode;
···
 	&dev_attr_bootstatus.attr,
 	&dev_attr_status.attr,
 	&dev_attr_nowayout.attr,
+	&dev_attr_pretimeout_governor.attr,
 	NULL,
 };
 
···
 		return PTR_ERR(dev);
 	}
 
+	ret = watchdog_register_pretimeout(wdd);
+	if (ret) {
+		device_destroy(&watchdog_class, devno);
+		watchdog_cdev_unregister(wdd);
+	}
+
 	return ret;
 }
 
···
 
 void watchdog_dev_unregister(struct watchdog_device *wdd)
 {
+	watchdog_unregister_pretimeout(wdd);
 	device_destroy(&watchdog_class, wdd->wd_data->cdev.dev);
 	watchdog_cdev_unregister(wdd);
 }

drivers/watchdog/watchdog_pretimeout.c

···
+/*
+ * Copyright (C) 2015-2016 Mentor Graphics
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ */
+
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/watchdog.h>
+
+#include "watchdog_pretimeout.h"
+
+/* Default watchdog pretimeout governor */
+static struct watchdog_governor *default_gov;
+
+/* The spinlock protects default_gov, wdd->gov and pretimeout_list */
+static DEFINE_SPINLOCK(pretimeout_lock);
+
+/* List of watchdog devices, which can generate a pretimeout event */
+static LIST_HEAD(pretimeout_list);
+
+struct watchdog_pretimeout {
+	struct watchdog_device		*wdd;
+	struct list_head		entry;
+};
+
+int watchdog_pretimeout_governor_get(struct watchdog_device *wdd, char *buf)
+{
+	int count = 0;
+
+	spin_lock_irq(&pretimeout_lock);
+	if (wdd->gov)
+		count = sprintf(buf, "%s\n", wdd->gov->name);
+	spin_unlock_irq(&pretimeout_lock);
+
+	return count;
+}
+
+void watchdog_notify_pretimeout(struct watchdog_device *wdd)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&pretimeout_lock, flags);
+	if (!wdd->gov) {
+		spin_unlock_irqrestore(&pretimeout_lock, flags);
+		return;
+	}
+
+	wdd->gov->pretimeout(wdd);
+	spin_unlock_irqrestore(&pretimeout_lock, flags);
+}
+EXPORT_SYMBOL_GPL(watchdog_notify_pretimeout);
+
+int watchdog_register_governor(struct watchdog_governor *gov)
+{
+	struct watchdog_pretimeout *p;
+
+	if (!default_gov) {
+		spin_lock_irq(&pretimeout_lock);
+		default_gov = gov;
+
+		list_for_each_entry(p, &pretimeout_list, entry)
+			if (!p->wdd->gov)
+				p->wdd->gov = default_gov;
+		spin_unlock_irq(&pretimeout_lock);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(watchdog_register_governor);
+
+void watchdog_unregister_governor(struct watchdog_governor *gov)
+{
+	struct watchdog_pretimeout *p;
+
+	spin_lock_irq(&pretimeout_lock);
+	if (gov == default_gov)
+		default_gov = NULL;
+
+	list_for_each_entry(p, &pretimeout_list, entry)
+		if (p->wdd->gov == gov)
+			p->wdd->gov = default_gov;
+	spin_unlock_irq(&pretimeout_lock);
+}
+EXPORT_SYMBOL(watchdog_unregister_governor);
+
+int watchdog_register_pretimeout(struct watchdog_device *wdd)
+{
+	struct watchdog_pretimeout *p;
+
+	if (!(wdd->info->options & WDIOF_PRETIMEOUT))
+		return 0;
+
+	p = kzalloc(sizeof(*p), GFP_KERNEL);
+	if (!p)
+		return -ENOMEM;
+
+	spin_lock_irq(&pretimeout_lock);
+	list_add(&p->entry, &pretimeout_list);
+	p->wdd = wdd;
+	wdd->gov = default_gov;
+	spin_unlock_irq(&pretimeout_lock);
+
+	return 0;
+}
+
+void watchdog_unregister_pretimeout(struct watchdog_device *wdd)
+{
+	struct watchdog_pretimeout *p, *t;
+
+	if (!(wdd->info->options & WDIOF_PRETIMEOUT))
+		return;
+
+	spin_lock_irq(&pretimeout_lock);
+	wdd->gov = NULL;
+
+	list_for_each_entry_safe(p, t, &pretimeout_list, entry) {
+		if (p->wdd == wdd) {
+			list_del(&p->entry);
+			break;
+		}
+	}
+	spin_unlock_irq(&pretimeout_lock);
+
+	kfree(p);
+}

drivers/watchdog/watchdog_pretimeout.h

···
+#ifndef __WATCHDOG_PRETIMEOUT_H
+#define __WATCHDOG_PRETIMEOUT_H
+
+#define WATCHDOG_GOV_NAME_MAXLEN	20
+
+struct watchdog_device;
+
+struct watchdog_governor {
+	const char	name[WATCHDOG_GOV_NAME_MAXLEN];
+	void		(*pretimeout)(struct watchdog_device *wdd);
+};
+
+#if IS_ENABLED(CONFIG_WATCHDOG_PRETIMEOUT_GOV)
+/* Interfaces to watchdog pretimeout governors */
+int watchdog_register_governor(struct watchdog_governor *gov);
+void watchdog_unregister_governor(struct watchdog_governor *gov);
+
+/* Interfaces to watchdog_dev.c */
+int watchdog_register_pretimeout(struct watchdog_device *wdd);
+void watchdog_unregister_pretimeout(struct watchdog_device *wdd);
+int watchdog_pretimeout_governor_get(struct watchdog_device *wdd, char *buf);
+
+#else
+static inline int watchdog_register_pretimeout(struct watchdog_device *wdd)
+{
+	return 0;
+}
+
+static inline void watchdog_unregister_pretimeout(struct watchdog_device *wdd)
+{
+}
+
+static inline int watchdog_pretimeout_governor_get(struct watchdog_device *wdd,
+						   char *buf)
+{
+	return -EINVAL;
+}
+#endif
+
+#endif

include/linux/watchdog.h

···
 struct watchdog_ops;
 struct watchdog_device;
 struct watchdog_core_data;
+struct watchdog_governor;
 
 /** struct watchdog_ops - The watchdog-devices operations
  *
···
  *		watchdog device.
  * @info:	Pointer to a watchdog_info structure.
  * @ops:	Pointer to the list of watchdog operations.
+ * @gov:	Pointer to watchdog pretimeout governor.
  * @bootstatus:	Status of the watchdog device at boot.
  * @timeout:	The watchdog devices timeout value (in seconds).
  * @pretimeout: The watchdog devices pre_timeout value.
···
 	const struct attribute_group **groups;
 	const struct watchdog_info *info;
 	const struct watchdog_ops *ops;
+	const struct watchdog_governor *gov;
 	unsigned int bootstatus;
 	unsigned int timeout;
 	unsigned int pretimeout;
···
 {
 	return wdd->driver_data;
 }
+
+/* Use the following functions to report watchdog pretimeout event */
+#if IS_ENABLED(CONFIG_WATCHDOG_PRETIMEOUT_GOV)
+void watchdog_notify_pretimeout(struct watchdog_device *wdd);
+#else
+static inline void watchdog_notify_pretimeout(struct watchdog_device *wdd)
+{
+	pr_alert("watchdog%d: pretimeout event\n", wdd->id);
+}
+#endif
 
 /* drivers/watchdog/watchdog_core.c */
 void watchdog_set_restart_priority(struct watchdog_device *wdd, int priority);