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Wim Van Sebroeck43316042011-07-22 18:55:18 +00001The Linux WatchDog Timer Driver Core kernel API.
2===============================================
Fabio Porcedda30482532013-01-08 11:04:10 +01003Last reviewed: 12-Feb-2013
Wim Van Sebroeck43316042011-07-22 18:55:18 +00004
5Wim Van Sebroeck <wim@iguana.be>
6
7Introduction
8------------
9This document does not describe what a WatchDog Timer (WDT) Driver or Device is.
10It also does not describe the API which can be used by user space to communicate
11with a WatchDog Timer. If you want to know this then please read the following
12file: Documentation/watchdog/watchdog-api.txt .
13
14So what does this document describe? It describes the API that can be used by
15WatchDog Timer Drivers that want to use the WatchDog Timer Driver Core
16Framework. This framework provides all interfacing towards user space so that
17the same code does not have to be reproduced each time. This also means that
18a watchdog timer driver then only needs to provide the different routines
19(operations) that control the watchdog timer (WDT).
20
21The API
22-------
23Each watchdog timer driver that wants to use the WatchDog Timer Driver Core
24must #include <linux/watchdog.h> (you would have to do this anyway when
25writing a watchdog device driver). This include file contains following
26register/unregister routines:
27
28extern int watchdog_register_device(struct watchdog_device *);
29extern void watchdog_unregister_device(struct watchdog_device *);
30
31The watchdog_register_device routine registers a watchdog timer device.
32The parameter of this routine is a pointer to a watchdog_device structure.
33This routine returns zero on success and a negative errno code for failure.
34
35The watchdog_unregister_device routine deregisters a registered watchdog timer
36device. The parameter of this routine is the pointer to the registered
37watchdog_device structure.
38
Jean-Baptiste Theouef901742015-06-09 09:55:02 -070039The watchdog subsystem includes an registration deferral mechanism,
40which allows you to register an watchdog as early as you wish during
41the boot process.
42
Wim Van Sebroeck43316042011-07-22 18:55:18 +000043The watchdog device structure looks like this:
44
45struct watchdog_device {
Alan Cox45f5fed2012-05-10 21:48:59 +020046 int id;
Alan Coxd6b469d2012-05-11 12:00:20 +020047 struct device *parent;
Guenter Roeckfaa58472016-01-03 15:11:56 -080048 const struct attribute_group **groups;
Wim Van Sebroeck43316042011-07-22 18:55:18 +000049 const struct watchdog_info *info;
50 const struct watchdog_ops *ops;
Wim Van Sebroeck2fa03562011-07-22 18:56:38 +000051 unsigned int bootstatus;
Wim Van Sebroeck014d6942011-07-22 18:58:21 +000052 unsigned int timeout;
Wim Van Sebroeck3f43f682011-07-22 19:00:16 +000053 unsigned int min_timeout;
54 unsigned int max_timeout;
Damien Riegele1313192015-11-20 16:54:51 -050055 struct notifier_block reboot_nb;
Damien Riegel2165bf52015-11-16 12:27:59 -050056 struct notifier_block restart_nb;
Wim Van Sebroeck43316042011-07-22 18:55:18 +000057 void *driver_data;
Guenter Roeckb4ffb192015-12-25 16:01:42 -080058 struct watchdog_core_data *wd_data;
Wim Van Sebroeck43316042011-07-22 18:55:18 +000059 unsigned long status;
Jean-Baptiste Theouef901742015-06-09 09:55:02 -070060 struct list_head deferred;
Wim Van Sebroeck43316042011-07-22 18:55:18 +000061};
62
63It contains following fields:
Alan Cox45f5fed2012-05-10 21:48:59 +020064* id: set by watchdog_register_device, id 0 is special. It has both a
65 /dev/watchdog0 cdev (dynamic major, minor 0) as well as the old
66 /dev/watchdog miscdev. The id is set automatically when calling
67 watchdog_register_device.
Alan Coxd6b469d2012-05-11 12:00:20 +020068* parent: set this to the parent device (or NULL) before calling
69 watchdog_register_device.
Guenter Roeckfaa58472016-01-03 15:11:56 -080070* groups: List of sysfs attribute groups to create when creating the watchdog
71 device.
Wim Van Sebroeck43316042011-07-22 18:55:18 +000072* info: a pointer to a watchdog_info structure. This structure gives some
73 additional information about the watchdog timer itself. (Like it's unique name)
74* ops: a pointer to the list of watchdog operations that the watchdog supports.
Wim Van Sebroeck014d6942011-07-22 18:58:21 +000075* timeout: the watchdog timer's timeout value (in seconds).
Wim Van Sebroeck3f43f682011-07-22 19:00:16 +000076* min_timeout: the watchdog timer's minimum timeout value (in seconds).
77* max_timeout: the watchdog timer's maximum timeout value (in seconds).
Damien Riegele1313192015-11-20 16:54:51 -050078* reboot_nb: notifier block that is registered for reboot notifications, for
79 internal use only. If the driver calls watchdog_stop_on_reboot, watchdog core
80 will stop the watchdog on such notifications.
Damien Riegel2165bf52015-11-16 12:27:59 -050081* restart_nb: notifier block that is registered for machine restart, for
82 internal use only. If a watchdog is capable of restarting the machine, it
83 should define ops->restart. Priority can be changed through
84 watchdog_set_restart_priority.
Wim Van Sebroeck2fa03562011-07-22 18:56:38 +000085* bootstatus: status of the device after booting (reported with watchdog
86 WDIOF_* status bits).
Wim Van Sebroeck43316042011-07-22 18:55:18 +000087* driver_data: a pointer to the drivers private data of a watchdog device.
Devendra Naga2deca732012-05-14 14:33:37 +053088 This data should only be accessed via the watchdog_set_drvdata and
Wim Van Sebroeck43316042011-07-22 18:55:18 +000089 watchdog_get_drvdata routines.
Guenter Roeckb4ffb192015-12-25 16:01:42 -080090* wd_data: a pointer to watchdog core internal data.
Wim Van Sebroeck43316042011-07-22 18:55:18 +000091* status: this field contains a number of status bits that give extra
Wim Van Sebroeck234445b2011-07-22 18:57:55 +000092 information about the status of the device (Like: is the watchdog timer
Guenter Roeckb4ffb192015-12-25 16:01:42 -080093 running/active, or is the nowayout bit set).
Jean-Baptiste Theouef901742015-06-09 09:55:02 -070094* deferred: entry in wtd_deferred_reg_list which is used to
95 register early initialized watchdogs.
Wim Van Sebroeck43316042011-07-22 18:55:18 +000096
97The list of watchdog operations is defined as:
98
99struct watchdog_ops {
100 struct module *owner;
101 /* mandatory operations */
102 int (*start)(struct watchdog_device *);
103 int (*stop)(struct watchdog_device *);
104 /* optional operations */
105 int (*ping)(struct watchdog_device *);
Wim Van Sebroeck2fa03562011-07-22 18:56:38 +0000106 unsigned int (*status)(struct watchdog_device *);
Wim Van Sebroeck014d6942011-07-22 18:58:21 +0000107 int (*set_timeout)(struct watchdog_device *, unsigned int);
Viresh Kumarfd7b6732012-03-16 09:14:00 +0100108 unsigned int (*get_timeleft)(struct watchdog_device *);
Damien Riegel2165bf52015-11-16 12:27:59 -0500109 int (*restart)(struct watchdog_device *);
Guenter Roeckb4ffb192015-12-25 16:01:42 -0800110 void (*ref)(struct watchdog_device *) __deprecated;
111 void (*unref)(struct watchdog_device *) __deprecated;
Wim Van Sebroeck78d88fc2011-07-22 18:59:49 +0000112 long (*ioctl)(struct watchdog_device *, unsigned int, unsigned long);
Wim Van Sebroeck43316042011-07-22 18:55:18 +0000113};
114
115It is important that you first define the module owner of the watchdog timer
116driver's operations. This module owner will be used to lock the module when
117the watchdog is active. (This to avoid a system crash when you unload the
118module and /dev/watchdog is still open).
Hans de Goedee907df32012-05-22 11:40:26 +0200119
Wim Van Sebroeck43316042011-07-22 18:55:18 +0000120Some operations are mandatory and some are optional. The mandatory operations
121are:
122* start: this is a pointer to the routine that starts the watchdog timer
123 device.
124 The routine needs a pointer to the watchdog timer device structure as a
125 parameter. It returns zero on success or a negative errno code for failure.
126* stop: with this routine the watchdog timer device is being stopped.
127 The routine needs a pointer to the watchdog timer device structure as a
128 parameter. It returns zero on success or a negative errno code for failure.
129 Some watchdog timer hardware can only be started and not be stopped. The
130 driver supporting this hardware needs to make sure that a start and stop
131 routine is being provided. This can be done by using a timer in the driver
132 that regularly sends a keepalive ping to the watchdog timer hardware.
133
134Not all watchdog timer hardware supports the same functionality. That's why
135all other routines/operations are optional. They only need to be provided if
136they are supported. These optional routines/operations are:
137* ping: this is the routine that sends a keepalive ping to the watchdog timer
138 hardware.
139 The routine needs a pointer to the watchdog timer device structure as a
140 parameter. It returns zero on success or a negative errno code for failure.
141 Most hardware that does not support this as a separate function uses the
142 start function to restart the watchdog timer hardware. And that's also what
143 the watchdog timer driver core does: to send a keepalive ping to the watchdog
144 timer hardware it will either use the ping operation (when available) or the
145 start operation (when the ping operation is not available).
Wim Van Sebroeckc2dc00e2011-07-22 18:57:23 +0000146 (Note: the WDIOC_KEEPALIVE ioctl call will only be active when the
147 WDIOF_KEEPALIVEPING bit has been set in the option field on the watchdog's
148 info structure).
Wim Van Sebroeck2fa03562011-07-22 18:56:38 +0000149* status: this routine checks the status of the watchdog timer device. The
150 status of the device is reported with watchdog WDIOF_* status flags/bits.
Wim Van Sebroeck014d6942011-07-22 18:58:21 +0000151* set_timeout: this routine checks and changes the timeout of the watchdog
152 timer device. It returns 0 on success, -EINVAL for "parameter out of range"
Hans de Goedeb10f7c12011-09-12 11:56:59 +0200153 and -EIO for "could not write value to the watchdog". On success this
154 routine should set the timeout value of the watchdog_device to the
155 achieved timeout value (which may be different from the requested one
156 because the watchdog does not necessarily has a 1 second resolution).
Wim Van Sebroeck014d6942011-07-22 18:58:21 +0000157 (Note: the WDIOF_SETTIMEOUT needs to be set in the options field of the
158 watchdog's info structure).
Viresh Kumarfd7b6732012-03-16 09:14:00 +0100159* get_timeleft: this routines returns the time that's left before a reset.
Damien Riegel2165bf52015-11-16 12:27:59 -0500160* restart: this routine restarts the machine. It returns 0 on success or a
161 negative errno code for failure.
Wim Van Sebroeck78d88fc2011-07-22 18:59:49 +0000162* ioctl: if this routine is present then it will be called first before we do
163 our own internal ioctl call handling. This routine should return -ENOIOCTLCMD
164 if a command is not supported. The parameters that are passed to the ioctl
165 call are: watchdog_device, cmd and arg.
Wim Van Sebroeck43316042011-07-22 18:55:18 +0000166
Guenter Roeckb4ffb192015-12-25 16:01:42 -0800167The 'ref' and 'unref' operations are no longer used and deprecated.
168
Wim Van Sebroeck43316042011-07-22 18:55:18 +0000169The status bits should (preferably) be set with the set_bit and clear_bit alike
170bit-operations. The status bits that are defined are:
Wim Van Sebroeck234445b2011-07-22 18:57:55 +0000171* WDOG_ACTIVE: this status bit indicates whether or not a watchdog timer device
172 is active or not. When the watchdog is active after booting, then you should
173 set this status bit (Note: when you register the watchdog timer device with
174 this bit set, then opening /dev/watchdog will skip the start operation)
Wim Van Sebroeck7e192b92011-07-22 18:59:17 +0000175* WDOG_NO_WAY_OUT: this bit stores the nowayout setting for the watchdog.
176 If this bit is set then the watchdog timer will not be able to stop.
Wim Van Sebroeck017cf082011-07-22 18:58:54 +0000177
Wim Van Sebroeckff0b3cd2011-11-29 16:24:16 +0100178 To set the WDOG_NO_WAY_OUT status bit (before registering your watchdog
179 timer device) you can either:
180 * set it statically in your watchdog_device struct with
181 .status = WATCHDOG_NOWAYOUT_INIT_STATUS,
182 (this will set the value the same as CONFIG_WATCHDOG_NOWAYOUT) or
183 * use the following helper function:
184 static inline void watchdog_set_nowayout(struct watchdog_device *wdd, int nowayout)
185
Wim Van Sebroeck7e192b92011-07-22 18:59:17 +0000186Note: The WatchDog Timer Driver Core supports the magic close feature and
187the nowayout feature. To use the magic close feature you must set the
188WDIOF_MAGICCLOSE bit in the options field of the watchdog's info structure.
189The nowayout feature will overrule the magic close feature.
Wim Van Sebroeck43316042011-07-22 18:55:18 +0000190
191To get or set driver specific data the following two helper functions should be
192used:
193
194static inline void watchdog_set_drvdata(struct watchdog_device *wdd, void *data)
195static inline void *watchdog_get_drvdata(struct watchdog_device *wdd)
196
197The watchdog_set_drvdata function allows you to add driver specific data. The
198arguments of this function are the watchdog device where you want to add the
199driver specific data to and a pointer to the data itself.
200
201The watchdog_get_drvdata function allows you to retrieve driver specific data.
202The argument of this function is the watchdog device where you want to retrieve
Masanari Iidae1986522012-02-11 00:09:20 +0900203data from. The function returns the pointer to the driver specific data.
Fabio Porcedda30482532013-01-08 11:04:10 +0100204
205To initialize the timeout field, the following function can be used:
206
207extern int watchdog_init_timeout(struct watchdog_device *wdd,
208 unsigned int timeout_parm, struct device *dev);
209
210The watchdog_init_timeout function allows you to initialize the timeout field
211using the module timeout parameter or by retrieving the timeout-sec property from
212the device tree (if the module timeout parameter is invalid). Best practice is
213to set the default timeout value as timeout value in the watchdog_device and
214then use this function to set the user "preferred" timeout value.
215This routine returns zero on success and a negative errno code for failure.
Damien Riegel2165bf52015-11-16 12:27:59 -0500216
Damien Riegele1313192015-11-20 16:54:51 -0500217To disable the watchdog on reboot, the user must call the following helper:
218
219static inline void watchdog_stop_on_reboot(struct watchdog_device *wdd);
220
Damien Riegel2165bf52015-11-16 12:27:59 -0500221To change the priority of the restart handler the following helper should be
222used:
223
224void watchdog_set_restart_priority(struct watchdog_device *wdd, int priority);
225
226User should follow the following guidelines for setting the priority:
227* 0: should be called in last resort, has limited restart capabilities
228* 128: default restart handler, use if no other handler is expected to be
229 available, and/or if restart is sufficient to restart the entire system
230* 255: highest priority, will preempt all other restart handlers