watchdog: pretimeout: add noop pretimeout governor

The change adds noop watchdog pretimeout governor, only an
informational message is printed to the kernel log buffer when a
watchdog triggers a pretimeout event.

While introducing the first pretimeout governor the selected design
assumes that the default pretimeout governor is selected by its name
and it is always built-in, thus the default pretimeout governor can
not be unregistered and the correspondent check can be removed from
the watchdog_unregister_governor() function.

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]>

drivers/watchdog/Kconfig

···
 	help
 	  The option allows to select watchdog pretimeout governors.
 
+if WATCHDOG_PRETIMEOUT_GOV
+
+choice
+	prompt "Default Watchdog Pretimeout Governor"
+	default WATCHDOG_PRETIMEOUT_DEFAULT_GOV_PANIC
+	help
+	  This option selects a default watchdog pretimeout governor.
+	  The governor takes its action, if a watchdog is capable
+	  to report a pretimeout event.
+
+config WATCHDOG_PRETIMEOUT_DEFAULT_GOV_NOOP
+	bool "noop"
+	select WATCHDOG_PRETIMEOUT_GOV_NOOP
+	help
+	  Use noop watchdog pretimeout governor by default. If noop
+	  governor is selected by a user, write a short message to
+	  the kernel log buffer and don't do any system changes.
+
+endchoice
+
+config WATCHDOG_PRETIMEOUT_GOV_NOOP
+	tristate "Noop watchdog pretimeout governor"
+	help
+	  Noop watchdog pretimeout governor, only an informational
+	  message is added to kernel log buffer.
+
+endif # WATCHDOG_PRETIMEOUT_GOV
+
 endif # WATCHDOG

drivers/watchdog/Makefile

···
 
 watchdog-$(CONFIG_WATCHDOG_PRETIMEOUT_GOV)	+= watchdog_pretimeout.o
 
+obj-$(CONFIG_WATCHDOG_PRETIMEOUT_GOV_NOOP)	+= pretimeout_noop.o
+
 # Only one watchdog can succeed. We probe the ISA/PCI/USB based
 # watchdog-cards first, then the architecture specific watchdog
 # drivers and then the architecture independent "softdog" driver.

drivers/watchdog/pretimeout_noop.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/module.h>
+#include <linux/printk.h>
+#include <linux/watchdog.h>
+
+#include "watchdog_pretimeout.h"
+
+/**
+ * pretimeout_noop - No operation on watchdog pretimeout event
+ * @wdd - watchdog_device
+ *
+ * This function prints a message about pretimeout to kernel log.
+ */
+static void pretimeout_noop(struct watchdog_device *wdd)
+{
+	pr_alert("watchdog%d: pretimeout event\n", wdd->id);
+}
+
+static struct watchdog_governor watchdog_gov_noop = {
+	.name		= "noop",
+	.pretimeout	= pretimeout_noop,
+};
+
+static int __init watchdog_gov_noop_register(void)
+{
+	return watchdog_register_governor(&watchdog_gov_noop);
+}
+
+static void __exit watchdog_gov_noop_unregister(void)
+{
+	watchdog_unregister_governor(&watchdog_gov_noop);
+}
+module_init(watchdog_gov_noop_register);
+module_exit(watchdog_gov_noop_unregister);
+
+MODULE_AUTHOR("Vladimir Zapolskiy <[e-mail]>");
+MODULE_DESCRIPTION("Panic watchdog pretimeout governor");
+MODULE_LICENSE("GPL");

drivers/watchdog/watchdog_pretimeout.h

···
 void watchdog_unregister_pretimeout(struct watchdog_device *wdd);
 int watchdog_pretimeout_governor_get(struct watchdog_device *wdd, char *buf);
 
+#if IS_ENABLED(CONFIG_WATCHDOG_PRETIMEOUT_DEFAULT_GOV_NOOP)
+#define WATCHDOG_PRETIMEOUT_DEFAULT_GOV		"noop"
+#endif
+
 #else
 static inline int watchdog_register_pretimeout(struct watchdog_device *wdd)
 {