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 <[email protected]>
Signed-off-by: Wim Van Sebroeck <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>
Acked-by: Wolfram Sang <[email protected]>

Documentation/watchdog/00-INDEX

@@ -8,6 +8,8 @@ src/
 	- 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

@@ -0,0 +1,119 @@
+The Linux WatchDog Timer Driver Core kernel API.
+===============================================
+Last reviewed: 22-Jul-2011
+
+Wim Van Sebroeck <[email protected]>
+
+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

@@ -28,6 +28,17 @@ menuconfig WATCHDOG
 
 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

@@ -2,6 +2,10 @@
 # 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

@@ -0,0 +1,101 @@
+/*
+ *	watchdog_core.c
+ *
+ *	(c) Copyright 2008-2011 Alan Cox <[email protected]>,
+ *						All Rights Reserved.
+ *
+ *	(c) Copyright 2008-2011 Wim Van Sebroeck <[email protected]>.
+ *
+ *	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 <[email protected]>,
+ *	  Rob Radez <[email protected]>,
+ *	  Rusty Lynch <[email protected]>
+ *	  Satyam Sharma <[email protected]>
+ *	  Randy Dunlap <[email protected]>
+ *
+ *	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 <[email protected]>");
+MODULE_AUTHOR("Wim Van Sebroeck <[email protected]>");
+MODULE_DESCRIPTION("WatchDog Timer Driver Core");
+MODULE_LICENSE("GPL");