1 ==============================================
2 The Linux WatchDog Timer Driver Core kernel AP
3 ==============================================
4
5 Last reviewed: 12-Feb-2013
6
7 Wim Van Sebroeck <wim@iguana.be>
8
9 Introduction
10 ------------
11 This document does not describe what a WatchDo
12 It also does not describe the API which can be
13 with a WatchDog Timer. If you want to know thi
14 file: Documentation/watchdog/watchdog-api.rst
15
16 So what does this document describe? It descri
17 WatchDog Timer Drivers that want to use the Wa
18 Framework. This framework provides all interfa
19 the same code does not have to be reproduced e
20 a watchdog timer driver then only needs to pro
21 (operations) that control the watchdog timer (
22
23 The API
24 -------
25 Each watchdog timer driver that wants to use t
26 must #include <linux/watchdog.h> (you would ha
27 writing a watchdog device driver). This includ
28 register/unregister routines::
29
30 extern int watchdog_register_device(st
31 extern void watchdog_unregister_device
32
33 The watchdog_register_device routine registers
34 The parameter of this routine is a pointer to
35 This routine returns zero on success and a neg
36
37 The watchdog_unregister_device routine deregis
38 device. The parameter of this routine is the p
39 watchdog_device structure.
40
41 The watchdog subsystem includes an registratio
42 which allows you to register an watchdog as ea
43 the boot process.
44
45 The watchdog device structure looks like this:
46
47 struct watchdog_device {
48 int id;
49 struct device *parent;
50 const struct attribute_group **groups;
51 const struct watchdog_info *info;
52 const struct watchdog_ops *ops;
53 const struct watchdog_governor *gov;
54 unsigned int bootstatus;
55 unsigned int timeout;
56 unsigned int pretimeout;
57 unsigned int min_timeout;
58 unsigned int max_timeout;
59 unsigned int min_hw_heartbeat_ms;
60 unsigned int max_hw_heartbeat_ms;
61 struct notifier_block reboot_nb;
62 struct notifier_block restart_nb;
63 void *driver_data;
64 struct watchdog_core_data *wd_data;
65 unsigned long status;
66 struct list_head deferred;
67 };
68
69 It contains following fields:
70
71 * id: set by watchdog_register_device, id 0 is
72 /dev/watchdog0 cdev (dynamic major, minor 0)
73 /dev/watchdog miscdev. The id is set automat
74 watchdog_register_device.
75 * parent: set this to the parent device (or NU
76 watchdog_register_device.
77 * groups: List of sysfs attribute groups to cr
78 device.
79 * info: a pointer to a watchdog_info structure
80 additional information about the watchdog ti
81 * ops: a pointer to the list of watchdog opera
82 * gov: a pointer to the assigned watchdog devi
83 * timeout: the watchdog timer's timeout value
84 This is the time after which the system will
85 not send a heartbeat request if WDOG_ACTIVE
86 * pretimeout: the watchdog timer's pretimeout
87 * min_timeout: the watchdog timer's minimum ti
88 If set, the minimum configurable value for '
89 * max_timeout: the watchdog timer's maximum ti
90 as seen from userspace. If set, the maximum
91 'timeout'. Not used if max_hw_heartbeat_ms i
92 * min_hw_heartbeat_ms: Hardware limit for mini
93 in milli-seconds. This value is normally 0;
94 if the hardware can not tolerate lower inter
95 * max_hw_heartbeat_ms: Maximum hardware heartb
96 If set, the infrastructure will send heartbe
97 if 'timeout' is larger than max_hw_heartbeat
98 is set and userspace failed to send a heartb
99 seconds. max_hw_heartbeat_ms must be set if
100 the stop function.
101 * reboot_nb: notifier block that is registered
102 internal use only. If the driver calls watch
103 will stop the watchdog on such notifications
104 * restart_nb: notifier block that is registere
105 internal use only. If a watchdog is capable
106 should define ops->restart. Priority can be
107 watchdog_set_restart_priority.
108 * bootstatus: status of the device after booti
109 WDIOF_* status bits).
110 * driver_data: a pointer to the drivers privat
111 This data should only be accessed via the wa
112 watchdog_get_drvdata routines.
113 * wd_data: a pointer to watchdog core internal
114 * status: this field contains a number of stat
115 information about the status of the device (
116 running/active, or is the nowayout bit set).
117 * deferred: entry in wtd_deferred_reg_list whi
118 register early initialized watchdogs.
119
120 The list of watchdog operations is defined as:
121
122 struct watchdog_ops {
123 struct module *owner;
124 /* mandatory operations */
125 int (*start)(struct watchdog_device *)
126 /* optional operations */
127 int (*stop)(struct watchdog_device *);
128 int (*ping)(struct watchdog_device *);
129 unsigned int (*status)(struct watchdog
130 int (*set_timeout)(struct watchdog_dev
131 int (*set_pretimeout)(struct watchdog_
132 unsigned int (*get_timeleft)(struct wa
133 int (*restart)(struct watchdog_device
134 long (*ioctl)(struct watchdog_device *
135 };
136
137 It is important that you first define the modu
138 driver's operations. This module owner will be
139 the watchdog is active. (This to avoid a syste
140 module and /dev/watchdog is still open).
141
142 Some operations are mandatory and some are opt
143 are:
144
145 * start: this is a pointer to the routine that
146 device.
147 The routine needs a pointer to the watchdog
148 parameter. It returns zero on success or a n
149
150 Not all watchdog timer hardware supports the s
151 all other routines/operations are optional. Th
152 they are supported. These optional routines/op
153
154 * stop: with this routine the watchdog timer d
155
156 The routine needs a pointer to the watchdog
157 parameter. It returns zero on success or a n
158 Some watchdog timer hardware can only be sta
159 driver supporting such hardware does not hav
160
161 If a driver has no stop function, the watchd
162 and start calling the driver's keepalive pin
163 device is closed.
164
165 If a watchdog driver does not implement the
166 max_hw_heartbeat_ms.
167 * ping: this is the routine that sends a keepa
168 hardware.
169
170 The routine needs a pointer to the watchdog
171 parameter. It returns zero on success or a n
172
173 Most hardware that does not support this as
174 start function to restart the watchdog timer
175 the watchdog timer driver core does: to send
176 timer hardware it will either use the ping o
177 start operation (when the ping operation is
178
179 (Note: the WDIOC_KEEPALIVE ioctl call will o
180 WDIOF_KEEPALIVEPING bit has been set in the
181 info structure).
182 * status: this routine checks the status of th
183 status of the device is reported with watchd
184
185 WDIOF_MAGICCLOSE and WDIOF_KEEPALIVEPING are
186 it is not necessary to report those bits fro
187 function is provided by the driver, the watc
188 provided in the bootstatus variable of struc
189
190 * set_timeout: this routine checks and changes
191 timer device. It returns 0 on success, -EINV
192 and -EIO for "could not write value to the w
193 routine should set the timeout value of the
194 achieved timeout value (which may be differe
195 because the watchdog does not necessarily ha
196
197 Drivers implementing max_hw_heartbeat_ms set
198 to the minimum of timeout and max_hw_heartbe
199 timeout value of the watchdog_device either
200 (if it is larger than max_hw_heartbeat_ms),
201 (Note: the WDIOF_SETTIMEOUT needs to be set
202 watchdog's info structure).
203
204 If the watchdog driver does not have to perf
205 watchdog_device.timeout, this callback can b
206
207 If set_timeout is not provided but, WDIOF_SE
208 infrastructure updates the timeout value of
209 to the requested value.
210
211 If the pretimeout feature is used (WDIOF_PRE
212 also take care of checking if pretimeout is
213 accordingly. This can't be done in the core
214 duty of the driver.
215 * set_pretimeout: this routine checks and chan
216 the watchdog. It is optional because not all
217 notification. The timeout value is not an ab
218 seconds before the actual timeout would happ
219 -EINVAL for "parameter out of range" and -EI
220 the watchdog". A value of 0 disables pretime
221
222 (Note: the WDIOF_PRETIMEOUT needs to be set
223 watchdog's info structure).
224
225 If the watchdog driver does not have to perf
226 watchdog_device.pretimeout, this callback ca
227 set_pretimeout is not provided but WDIOF_PRE
228 infrastructure updates the pretimeout value
229 to the requested value.
230
231 * get_timeleft: this routines returns the time
232 * restart: this routine restarts the machine.
233 negative errno code for failure.
234 * ioctl: if this routine is present then it wi
235 our own internal ioctl call handling. This r
236 if a command is not supported. The parameter
237 call are: watchdog_device, cmd and arg.
238
239 The status bits should (preferably) be set wit
240 bit-operations. The status bits that are defin
241
242 * WDOG_ACTIVE: this status bit indicates wheth
243 is active or not from user perspective. User
244 heartbeat requests to the driver while this
245 * WDOG_NO_WAY_OUT: this bit stores the nowayou
246 If this bit is set then the watchdog timer w
247 * WDOG_HW_RUNNING: Set by the watchdog driver
248 running. The bit must be set if the watchdog
249 stopped. The bit may also be set if the watc
250 booting, before the watchdog device is opene
251 infrastructure will send keepalives to the w
252 WDOG_ACTIVE is not set.
253 Note: when you register the watchdog timer d
254 then opening /dev/watchdog will skip the sta
255 request instead.
256
257 To set the WDOG_NO_WAY_OUT status bit (befor
258 timer device) you can either:
259
260 * set it statically in your watchdog_device
261
262 .status = WATCHDOG_NOWAYOUT_INIT_STATU
263
264 (this will set the value the same as CONFI
265 * use the following helper function::
266
267 static inline void watchdog_set_nowayo
268
269
270 Note:
271 The WatchDog Timer Driver Core supports the
272 the nowayout feature. To use the magic clos
273 WDIOF_MAGICCLOSE bit in the options field o
274
275 The nowayout feature will overrule the magic c
276
277 To get or set driver specific data the followi
278 used::
279
280 static inline void watchdog_set_drvdata(stru
281 void
282 static inline void *watchdog_get_drvdata(str
283
284 The watchdog_set_drvdata function allows you t
285 arguments of this function are the watchdog de
286 driver specific data to and a pointer to the d
287
288 The watchdog_get_drvdata function allows you t
289 The argument of this function is the watchdog
290 data from. The function returns the pointer to
291
292 To initialize the timeout field, the following
293
294 extern int watchdog_init_timeout(struct watc
295 unsigned in
296 struct devi
297
298 The watchdog_init_timeout function allows you
299 using the module timeout parameter or by retri
300 the device tree (if the module timeout paramet
301 to set the default timeout value as timeout va
302 then use this function to set the user "prefer
303 This routine returns zero on success and a neg
304
305 To disable the watchdog on reboot, the user mu
306
307 static inline void watchdog_stop_on_reboot(s
308
309 To disable the watchdog when unregistering the
310 the following helper. Note that this will only
311 nowayout flag is not set.
312
313 ::
314
315 static inline void watchdog_stop_on_unregist
316
317 To change the priority of the restart handler
318 used::
319
320 void watchdog_set_restart_priority(struct wa
321
322 User should follow the following guidelines fo
323
324 * 0: should be called in last resort, has limi
325 * 128: default restart handler, use if no othe
326 available, and/or if restart is sufficient t
327 * 255: highest priority, will preempt all othe
328
329 To raise a pretimeout notification, the follow
330
331 void watchdog_notify_pretimeout(struct watch
332
333 The function can be called in the interrupt co
334 governor framework (kbuild CONFIG_WATCHDOG_PRE
335 an action is taken by a preconfigured pretimeo
336 the watchdog device. If watchdog pretimeout go
337 enabled, watchdog_notify_pretimeout() prints a
338 the kernel log buffer.
339
340 To set the last known HW keepalive time for a
341 should be used::
342
343 int watchdog_set_last_hw_keepalive(struct wa
344 unsigned
345
346 This function must be called immediately after
347 sets the last known hardware heartbeat to have
348 current time. Calling this is only needed if t
349 when probe is called, and the watchdog can onl
350 min_hw_heartbeat_ms time has passed from the l
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.