watchdog: WatchDog Timer Driver Core - Add basic framework

The WatchDog Timer Driver Core is a framework
that contains the common code for all watchdog-driver's.
It also introduces a watchdog device structure and the
operations that go with it.

This is the introduction of this framework. This part
supports the minimal watchdog userspace API (or with
other words: the functionality to use /dev/watchdog's
open, release and write functionality as defined in
the simplest watchdog API). Extra functionality will
follow in the next set of patches.

Signed-off-by: Alan Cox <[e-mail]>
Signed-off-by: Wim Van Sebroeck <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
Acked-by: Wolfram Sang <[e-mail]>

Documentation/watchdog/00-INDEX

···
 	- directory holding watchdog related example programs.
 watchdog-api.txt
 	- description of the Linux Watchdog driver API.
+watchdog-kernel-api.txt
+	- description of the Linux WatchDog Timer Driver Core kernel API.
 watchdog-parameters.txt
 	- information on driver parameters (for drivers other than
 	  the ones that have driver-specific files here)

Documentation/watchdog/watchdog-kernel-api.txt

···
+The Linux WatchDog Timer Driver Core kernel API.
+===============================================
+Last reviewed: 22-Jul-2011
+
+Wim Van Sebroeck <[e-mail]>
+
+Introduction
+------------
+This document does not describe what a WatchDog Timer (WDT) Driver or Device is.
+It also does not describe the API which can be used by user space to communicate
+with a WatchDog Timer. If you want to know this then please read the following
+file: Documentation/watchdog/watchdog-api.txt .
+
+So what does this document describe? It describes the API that can be used by
+WatchDog Timer Drivers that want to use the WatchDog Timer Driver Core
+Framework. This framework provides all interfacing towards user space so that
+the same code does not have to be reproduced each time. This also means that
+a watchdog timer driver then only needs to provide the different routines
+(operations) that control the watchdog timer (WDT).
+
+The API
+-------
+Each watchdog timer driver that wants to use the WatchDog Timer Driver Core
+must #include <linux/watchdog.h> (you would have to do this anyway when
+writing a watchdog device driver). This include file contains following
+register/unregister routines:
+
+extern int watchdog_register_device(struct watchdog_device *);
+extern void watchdog_unregister_device(struct watchdog_device *);
+
+The watchdog_register_device routine registers a watchdog timer device.
+The parameter of this routine is a pointer to a watchdog_device structure.
+This routine returns zero on success and a negative errno code for failure.
+
+The watchdog_unregister_device routine deregisters a registered watchdog timer
+device. The parameter of this routine is the pointer to the registered
+watchdog_device structure.
+
+The watchdog device structure looks like this:
+
+struct watchdog_device {
+	const struct watchdog_info *info;
+	const struct watchdog_ops *ops;
+	void *driver_data;
+	unsigned long status;
+};
+
+It contains following fields:
+* 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.
+* driver_data: a pointer to the drivers private data of a watchdog device.
+  This data should only be accessed via the watchdog_set_drvadata and
+  watchdog_get_drvdata routines.
+* status: this field contains a number of status bits that give extra
+  information about the status of the device (Like: is the device opened via
+  the /dev/watchdog interface or not, ...).
+
+The list of watchdog operations is defined as:
+
+struct watchdog_ops {
+	struct module *owner;
+	/* mandatory operations */
+	int (*start)(struct watchdog_device *);
+	int (*stop)(struct watchdog_device *);
+	/* optional operations */
+	int (*ping)(struct watchdog_device *);
+};
+
+It is important that you first define the module owner of the watchdog timer
+driver's operations. This module owner will be used to lock the module when
+the watchdog is active. (This to avoid a system crash when you unload the
+module and /dev/watchdog is still open).
+Some operations are mandatory and some are optional. The mandatory operations
+are:
+* start: this is a pointer to the routine that starts the watchdog timer
+  device.
+  The routine needs a pointer to the watchdog timer device structure as a
+  parameter. It returns zero on success or a negative errno code for failure.
+* stop: with this routine the watchdog timer device is being stopped.
+  The routine needs a pointer to the watchdog timer device structure as a
+  parameter. It returns zero on success or a negative errno code for failure.
+  Some watchdog timer hardware can only be started and not be stopped. The
+  driver supporting this hardware needs to make sure that a start and stop
+  routine is being provided. This can be done by using a timer in the driver
+  that regularly sends a keepalive ping to the watchdog timer hardware.
+
+Not all watchdog timer hardware supports the same functionality. That's why
+all other routines/operations are optional. They only need to be provided if
+they are supported. These optional routines/operations are:
+* ping: this is the routine that sends a keepalive ping to the watchdog timer
+  hardware.
+  The routine needs a pointer to the watchdog timer device structure as a
+  parameter. It returns zero on success or a negative errno code for failure.
+  Most hardware that does not support this as a separate function uses the
+  start function to restart the watchdog timer hardware. And that's also what
+  the watchdog timer driver core does: to send a keepalive ping to the watchdog
+  timer hardware it will either use the ping operation (when available) or the
+  start operation (when the ping operation is not available).
+
+The status bits should (preferably) be set with the set_bit and clear_bit alike
+bit-operations. The status bits that are defined are:
+* WDOG_DEV_OPEN: this status bit shows whether or not the watchdog device
+  was opened via /dev/watchdog.
+  (This bit should only be used by the WatchDog Timer Driver Core).
+
+To get or set driver specific data the following two helper functions should be
+used:
+
+static inline void watchdog_set_drvdata(struct watchdog_device *wdd, void *data)
+static inline void *watchdog_get_drvdata(struct watchdog_device *wdd)
+
+The watchdog_set_drvdata function allows you to add driver specific data. The
+arguments of this function are the watchdog device where you want to add the
+driver specific data to and a pointer to the data itself.
+
+The watchdog_get_drvdata function allows you to retrieve driver specific data.
+The argument of this function is the watchdog device where you want to retrieve
+data from. The function retruns the pointer to the driver specific data.

drivers/watchdog/Kconfig

···
 
 if WATCHDOG
 
+config WATCHDOG_CORE
+	bool "WatchDog Timer Driver Core"
+	---help---
+	  Say Y here if you want to use the new watchdog timer driver core.
+	  This driver provides a framework for all watchdog timer drivers
+	  and gives them the /dev/watchdog interface (and later also the
+	  sysfs interface).
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called watchdog.
+
 config WATCHDOG_NOWAYOUT
 	bool "Disable watchdog shutdown on close"
 	help

drivers/watchdog/Makefile

···
 # Makefile for the WatchDog device drivers.
 #
 
+# The WatchDog Timer Driver Core.
+watchdog-objs	+= watchdog_core.o watchdog_dev.o
+obj-$(CONFIG_WATCHDOG_CORE)	+= watchdog.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/watchdog_core.c

···
+/*
+ *	watchdog_core.c
+ *
+ *	(c) Copyright 2008-2011 Alan Cox <[e-mail]>,
+ *						All Rights Reserved.
+ *
+ *	(c) Copyright 2008-2011 Wim Van Sebroeck <[e-mail]>.
+ *
+ *	This source code is part of the generic code that can be used
+ *	by all the watchdog timer drivers.
+ *
+ *	Based on source code of the following authors:
+ *	  Matt Domsch <[e-mail]>,
+ *	  Rob Radez <[e-mail]>,
+ *	  Rusty Lynch <[e-mail]>
+ *	  Satyam Sharma <[e-mail]>
+ *	  Randy Dunlap <[e-mail]>
+ *
+ *	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.
+ *
+ *	Neither Alan Cox, CymruNet Ltd., Wim Van Sebroeck nor Iguana vzw.
+ *	admit liability nor provide warranty for any of this software.
+ *	This material is provided "AS-IS" and at no charge.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>	/* For EXPORT_SYMBOL/module stuff/... */
+#include <linux/types.h>	/* For standard types */
+#include <linux/errno.h>	/* For the -ENODEV/... values */
+#include <linux/kernel.h>	/* For printk/panic/... */
+#include <linux/watchdog.h>	/* For watchdog specific items */
+#include <linux/init.h>		/* For __init/__exit/... */
+
+#include "watchdog_dev.h"	/* For watchdog_dev_register/... */
+
+/**
+ * watchdog_register_device() - register a watchdog device
+ * @wdd: watchdog device
+ *
+ * Register a watchdog device with the kernel so that the
+ * watchdog timer can be accessed from userspace.
+ *
+ * A zero is returned on success and a negative errno code for
+ * failure.
+ */
+int watchdog_register_device(struct watchdog_device *wdd)
+{
+	int ret;
+
+	if (wdd == NULL || wdd->info == NULL || wdd->ops == NULL)
+		return -EINVAL;
+
+	/* Mandatory operations need to be supported */
+	if (wdd->ops->start == NULL || wdd->ops->stop == NULL)
+		return -EINVAL;
+
+	/*
+	 * Note: now that all watchdog_device data has been verified, we
+	 * will not check this anymore in other functions. If data gets
+	 * corrupted in a later stage then we expect a kernel panic!
+	 */
+
+	/* We only support 1 watchdog device via the /dev/watchdog interface */
+	ret = watchdog_dev_register(wdd);
+	if (ret) {
+		pr_err("error registering /dev/watchdog (err=%d).\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(watchdog_register_device);
+
+/**
+ * watchdog_unregister_device() - unregister a watchdog device
+ * @wdd: watchdog device to unregister
+ *
+ * Unregister a watchdog device that was previously successfully
+ * registered with watchdog_register_device().
+ */
+void watchdog_unregister_device(struct watchdog_device *wdd)
+{
+	int ret;
+
+	if (wdd == NULL)
+		return;
+
+	ret = watchdog_dev_unregister(wdd);
+	if (ret)
+		pr_err("error unregistering /dev/watchdog (err=%d).\n", ret);
+}
+EXPORT_SYMBOL_GPL(watchdog_unregister_device);
+
+MODULE_AUTHOR("Alan Cox <[e-mail]>");
+MODULE_AUTHOR("Wim Van Sebroeck <[e-mail]>");
+MODULE_DESCRIPTION("WatchDog Timer Driver Core");
+MODULE_LICENSE("GPL");

drivers/watchdog/watchdog_dev.c

···
+/*
+ *	watchdog_dev.c
+ *
+ *	(c) Copyright 2008-2011 Alan Cox <[e-mail]>,
+ *						All Rights Reserved.
+ *
+ *	(c) Copyright 2008-2011 Wim Van Sebroeck <[e-mail]>.
+ *
+ *
+ *	This source code is part of the generic code that can be used
+ *	by all the watchdog timer drivers.
+ *
+ *	This part of the generic code takes care of the following
+ *	misc device: /dev/watchdog.
+ *
+ *	Based on source code of the following authors:
+ *	  Matt Domsch <[e-mail]>,
+ *	  Rob Radez <[e-mail]>,
+ *	  Rusty Lynch <[e-mail]>
+ *	  Satyam Sharma <[e-mail]>
+ *	  Randy Dunlap <[e-mail]>
+ *
+ *	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.
+ *
+ *	Neither Alan Cox, CymruNet Ltd., Wim Van Sebroeck nor Iguana vzw.
+ *	admit liability nor provide warranty for any of this software.
+ *	This material is provided "AS-IS" and at no charge.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>	/* For module stuff/... */
+#include <linux/types.h>	/* For standard types (like size_t) */
+#include <linux/errno.h>	/* For the -ENODEV/... values */
+#include <linux/kernel.h>	/* For printk/panic/... */
+#include <linux/fs.h>		/* For file operations */
+#include <linux/watchdog.h>	/* For watchdog specific items */
+#include <linux/miscdevice.h>	/* For handling misc devices */
+#include <linux/init.h>		/* For __init/__exit/... */
+#include <linux/uaccess.h>	/* For copy_to_user/put_user/... */
+
+/* make sure we only register one /dev/watchdog device */
+static unsigned long watchdog_dev_busy;
+/* the watchdog device behind /dev/watchdog */
+static struct watchdog_device *wdd;
+
+/*
+ *	watchdog_ping: ping the watchdog.
+ *	@wddev: the watchdog device to ping
+ *
+ *	If the watchdog has no own ping operation then it needs to be
+ *	restarted via the start operation. This wrapper function does
+ *	exactly that.
+ */
+
+static int watchdog_ping(struct watchdog_device *wddev)
+{
+	if (wddev->ops->ping)
+		return wddev->ops->ping(wddev);  /* ping the watchdog */
+	else
+		return wddev->ops->start(wddev); /* restart the watchdog */
+}
+
+/*
+ *	watchdog_write: writes to the watchdog.
+ *	@file: file from VFS
+ *	@data: user address of data
+ *	@len: length of data
+ *	@ppos: pointer to the file offset
+ *
+ *	A write to a watchdog device is defined as a keepalive ping.
+ */
+
+static ssize_t watchdog_write(struct file *file, const char __user *data,
+						size_t len, loff_t *ppos)
+{
+	size_t i;
+	char c;
+
+	if (len == 0)
+		return 0;
+
+	for (i = 0; i != len; i++) {
+		if (get_user(c, data + i))
+			return -EFAULT;
+	}
+
+	/* someone wrote to us, so we send the watchdog a keepalive ping */
+	watchdog_ping(wdd);
+
+	return len;
+}
+
+/*
+ *	watchdog_open: open the /dev/watchdog device.
+ *	@inode: inode of device
+ *	@file: file handle to device
+ *
+ *	When the /dev/watchdog device gets opened, we start the watchdog.
+ *	Watch out: the /dev/watchdog device is single open, so we make sure
+ *	it can only be opened once.
+ */
+
+static int watchdog_open(struct inode *inode, struct file *file)
+{
+	int err = -EBUSY;
+
+	/* the watchdog is single open! */
+	if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status))
+		return -EBUSY;
+
+	/*
+	 * If the /dev/watchdog device is open, we don't want the module
+	 * to be unloaded.
+	 */
+	if (!try_module_get(wdd->ops->owner))
+		goto out;
+
+	err = wdd->ops->start(wdd);
+	if (err < 0)
+		goto out_mod;
+
+	/* dev/watchdog is a virtual (and thus non-seekable) filesystem */
+	return nonseekable_open(inode, file);
+
+out_mod:
+	module_put(wdd->ops->owner);
+out:
+	clear_bit(WDOG_DEV_OPEN, &wdd->status);
+	return err;
+}
+
+/*
+ *      watchdog_release: release the /dev/watchdog device.
+ *      @inode: inode of device
+ *      @file: file handle to device
+ *
+ *	This is the code for when /dev/watchdog gets closed.
+ */
+
+static int watchdog_release(struct inode *inode, struct file *file)
+{
+	int err;
+
+	err = wdd->ops->stop(wdd);
+	if (err != 0) {
+		pr_crit("%s: watchdog did not stop!\n", wdd->info->identity);
+		watchdog_ping(wdd);
+	}
+
+	/* Allow the owner module to be unloaded again */
+	module_put(wdd->ops->owner);
+
+	/* make sure that /dev/watchdog can be re-opened */
+	clear_bit(WDOG_DEV_OPEN, &wdd->status);
+
+	return 0;
+}
+
+static const struct file_operations watchdog_fops = {
+	.owner		= THIS_MODULE,
+	.write		= watchdog_write,
+	.open		= watchdog_open,
+	.release	= watchdog_release,
+};
+
+static struct miscdevice watchdog_miscdev = {
+	.minor		= WATCHDOG_MINOR,
+	.name		= "watchdog",
+	.fops		= &watchdog_fops,
+};
+
+/*
+ *	watchdog_dev_register:
+ *	@watchdog: watchdog device
+ *
+ *	Register a watchdog device as /dev/watchdog. /dev/watchdog
+ *	is actually a miscdevice and thus we set it up like that.
+ */
+
+int watchdog_dev_register(struct watchdog_device *watchdog)
+{
+	int err;
+
+	/* Only one device can register for /dev/watchdog */
+	if (test_and_set_bit(0, &watchdog_dev_busy)) {
+		pr_err("only one watchdog can use /dev/watchdog.\n");
+		return -EBUSY;
+	}
+
+	wdd = watchdog;
+
+	err = misc_register(&watchdog_miscdev);
+	if (err != 0) {
+		pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n",
+			watchdog->info->identity, WATCHDOG_MINOR, err);
+		goto out;
+	}
+
+	return 0;
+
+out:
+	wdd = NULL;
+	clear_bit(0, &watchdog_dev_busy);
+	return err;
+}
+
+/*
+ *	watchdog_dev_unregister:
+ *	@watchdog: watchdog device
+ *
+ *	Deregister the /dev/watchdog device.
+ */
+
+int watchdog_dev_unregister(struct watchdog_device *watchdog)
+{
+	/* Check that a watchdog device was registered in the past */
+	if (!test_bit(0, &watchdog_dev_busy) || !wdd)
+		return -ENODEV;
+
+	/* We can only unregister the watchdog device that was registered */
+	if (watchdog != wdd) {
+		pr_err("%s: watchdog was not registered as /dev/watchdog.\n",
+			watchdog->info->identity);
+		return -ENODEV;
+	}
+
+	misc_deregister(&watchdog_miscdev);
+	wdd = NULL;
+	clear_bit(0, &watchdog_dev_busy);
+	return 0;
+}

drivers/watchdog/watchdog_dev.h

···
+/*
+ *	watchdog_core.h
+ *
+ *	(c) Copyright 2008-2011 Alan Cox <[e-mail]>,
+ *						All Rights Reserved.
+ *
+ *	(c) Copyright 2008-2011 Wim Van Sebroeck <[e-mail]>.
+ *
+ *	This source code is part of the generic code that can be used
+ *	by all the watchdog timer drivers.
+ *
+ *	Based on source code of the following authors:
+ *	  Matt Domsch <[e-mail]>,
+ *	  Rob Radez <[e-mail]>,
+ *	  Rusty Lynch <[e-mail]>
+ *	  Satyam Sharma <[e-mail]>
+ *	  Randy Dunlap <[e-mail]>
+ *
+ *	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.
+ *
+ *	Neither Alan Cox, CymruNet Ltd., Wim Van Sebroeck nor Iguana vzw.
+ *	admit liability nor provide warranty for any of this software.
+ *	This material is provided "AS-IS" and at no charge.
+ */
+
+/*
+ *	Functions/procedures to be called by the core
+ */
+int watchdog_dev_register(struct watchdog_device *);
+int watchdog_dev_unregister(struct watchdog_device *);

include/linux/watchdog.h

···
 #define WATCHDOG_NOWAYOUT	0
 #endif
 
+struct watchdog_ops;
+struct watchdog_device;
+
+/** struct watchdog_ops - The watchdog-devices operations
+ *
+ * @owner:	The module owner.
+ * @start:	The routine for starting the watchdog device.
+ * @stop:	The routine for stopping the watchdog device.
+ * @ping:	The routine that sends a keepalive ping to the watchdog device.
+ *
+ * The watchdog_ops structure contains a list of low-level operations
+ * that control a watchdog device. It also contains the module that owns
+ * these operations. The start and stop function are mandatory, all other
+ * functions are optonal.
+ */
+struct watchdog_ops {
+	struct module *owner;
+	/* mandatory operations */
+	int (*start)(struct watchdog_device *);
+	int (*stop)(struct watchdog_device *);
+	/* optional operations */
+	int (*ping)(struct watchdog_device *);
+};
+
+/** struct watchdog_device - The structure that defines a watchdog device
+ *
+ * @info:	Pointer to a watchdog_info structure.
+ * @ops:	Pointer to the list of watchdog operations.
+ * @driver-data:Pointer to the drivers private data.
+ * @status:	Field that contains the devices internal status bits.
+ *
+ * The watchdog_device structure contains all information about a
+ * watchdog timer device.
+ *
+ * The driver-data field may not be accessed directly. It must be accessed
+ * via the watchdog_set_drvdata and watchdog_get_drvdata helpers.
+ */
+struct watchdog_device {
+	const struct watchdog_info *info;
+	const struct watchdog_ops *ops;
+	void *driver_data;
+	unsigned long status;
+/* Bit numbers for status flags */
+#define WDOG_DEV_OPEN		1	/* Opened via /dev/watchdog ? */
+};
+
+/* Use the following functions to manipulate watchdog driver specific data */
+static inline void watchdog_set_drvdata(struct watchdog_device *wdd, void *data)
+{
+	wdd->driver_data = data;
+}
+
+static inline void *watchdog_get_drvdata(struct watchdog_device *wdd)
+{
+	return wdd->driver_data;
+}
+
+/* drivers/watchdog/core/watchdog_core.c */
+extern int watchdog_register_device(struct watchdog_device *);
+extern void watchdog_unregister_device(struct watchdog_device *);
+
 #endif	/* __KERNEL__ */
 
 #endif  /* ifndef _LINUX_WATCHDOG_H */