blob: 086638f6c82d2e37d92e2aefa94243c5b1b74b13 [file] [log] [blame]
Wim Van Sebroeck43316042011-07-22 18:55:18 +00001The Linux WatchDog Timer Driver Core kernel API.
2===============================================
Hans de Goedee907df32012-05-22 11:40:26 +02003Last reviewed: 22-May-2012
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
39The watchdog device structure looks like this:
40
41struct watchdog_device {
Alan Cox45f5fed2012-05-10 21:48:59 +020042 int id;
43 struct cdev cdev;
Alan Coxd6b469d2012-05-11 12:00:20 +020044 struct device *dev;
45 struct device *parent;
Wim Van Sebroeck43316042011-07-22 18:55:18 +000046 const struct watchdog_info *info;
47 const struct watchdog_ops *ops;
Wim Van Sebroeck2fa03562011-07-22 18:56:38 +000048 unsigned int bootstatus;
Wim Van Sebroeck014d6942011-07-22 18:58:21 +000049 unsigned int timeout;
Wim Van Sebroeck3f43f682011-07-22 19:00:16 +000050 unsigned int min_timeout;
51 unsigned int max_timeout;
Wim Van Sebroeck43316042011-07-22 18:55:18 +000052 void *driver_data;
Hans de Goedef4e9c822012-05-22 11:40:26 +020053 struct mutex lock;
Wim Van Sebroeck43316042011-07-22 18:55:18 +000054 unsigned long status;
55};
56
57It contains following fields:
Alan Cox45f5fed2012-05-10 21:48:59 +020058* id: set by watchdog_register_device, id 0 is special. It has both a
59 /dev/watchdog0 cdev (dynamic major, minor 0) as well as the old
60 /dev/watchdog miscdev. The id is set automatically when calling
61 watchdog_register_device.
62* cdev: cdev for the dynamic /dev/watchdog<id> device nodes. This
63 field is also populated by watchdog_register_device.
Alan Coxd6b469d2012-05-11 12:00:20 +020064* dev: device under the watchdog class (created by watchdog_register_device).
65* parent: set this to the parent device (or NULL) before calling
66 watchdog_register_device.
Wim Van Sebroeck43316042011-07-22 18:55:18 +000067* info: a pointer to a watchdog_info structure. This structure gives some
68 additional information about the watchdog timer itself. (Like it's unique name)
69* ops: a pointer to the list of watchdog operations that the watchdog supports.
Wim Van Sebroeck014d6942011-07-22 18:58:21 +000070* timeout: the watchdog timer's timeout value (in seconds).
Wim Van Sebroeck3f43f682011-07-22 19:00:16 +000071* min_timeout: the watchdog timer's minimum timeout value (in seconds).
72* max_timeout: the watchdog timer's maximum timeout value (in seconds).
Wim Van Sebroeck2fa03562011-07-22 18:56:38 +000073* bootstatus: status of the device after booting (reported with watchdog
74 WDIOF_* status bits).
Wim Van Sebroeck43316042011-07-22 18:55:18 +000075* driver_data: a pointer to the drivers private data of a watchdog device.
Devendra Naga2deca732012-05-14 14:33:37 +053076 This data should only be accessed via the watchdog_set_drvdata and
Wim Van Sebroeck43316042011-07-22 18:55:18 +000077 watchdog_get_drvdata routines.
Hans de Goedef4e9c822012-05-22 11:40:26 +020078* lock: Mutex for WatchDog Timer Driver Core internal use only.
Wim Van Sebroeck43316042011-07-22 18:55:18 +000079* status: this field contains a number of status bits that give extra
Wim Van Sebroeck234445b2011-07-22 18:57:55 +000080 information about the status of the device (Like: is the watchdog timer
Wim Van Sebroeck7e192b92011-07-22 18:59:17 +000081 running/active, is the nowayout bit set, is the device opened via
82 the /dev/watchdog interface or not, ...).
Wim Van Sebroeck43316042011-07-22 18:55:18 +000083
84The list of watchdog operations is defined as:
85
86struct watchdog_ops {
87 struct module *owner;
88 /* mandatory operations */
89 int (*start)(struct watchdog_device *);
90 int (*stop)(struct watchdog_device *);
91 /* optional operations */
92 int (*ping)(struct watchdog_device *);
Wim Van Sebroeck2fa03562011-07-22 18:56:38 +000093 unsigned int (*status)(struct watchdog_device *);
Wim Van Sebroeck014d6942011-07-22 18:58:21 +000094 int (*set_timeout)(struct watchdog_device *, unsigned int);
Viresh Kumarfd7b6732012-03-16 09:14:00 +010095 unsigned int (*get_timeleft)(struct watchdog_device *);
Hans de Goedee907df32012-05-22 11:40:26 +020096 void (*ref)(struct watchdog_device *);
97 void (*unref)(struct watchdog_device *);
Wim Van Sebroeck78d88fc2011-07-22 18:59:49 +000098 long (*ioctl)(struct watchdog_device *, unsigned int, unsigned long);
Wim Van Sebroeck43316042011-07-22 18:55:18 +000099};
100
101It is important that you first define the module owner of the watchdog timer
102driver's operations. This module owner will be used to lock the module when
103the watchdog is active. (This to avoid a system crash when you unload the
104module and /dev/watchdog is still open).
Hans de Goedee907df32012-05-22 11:40:26 +0200105
106If the watchdog_device struct is dynamically allocated, just locking the module
107is not enough and a driver also needs to define the ref and unref operations to
108ensure the structure holding the watchdog_device does not go away.
109
110The simplest (and usually sufficient) implementation of this is to:
1111) Add a kref struct to the same structure which is holding the watchdog_device
1122) Define a release callback for the kref which frees the struct holding both
1133) Call kref_init on this kref *before* calling watchdog_register_device()
1144) Define a ref operation calling kref_get on this kref
1155) Define a unref operation calling kref_put on this kref
1166) When it is time to cleanup:
117 * Do not kfree() the struct holding both, the last kref_put will do this!
118 * *After* calling watchdog_unregister_device() call kref_put on the kref
119
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.
Hans de Goedee907df32012-05-22 11:40:26 +0200160* ref: the operation that calls kref_get on the kref of a dynamically
161 allocated watchdog_device struct.
162* unref: the operation that calls kref_put on the kref of a dynamically
163 allocated watchdog_device struct.
Wim Van Sebroeck78d88fc2011-07-22 18:59:49 +0000164* ioctl: if this routine is present then it will be called first before we do
165 our own internal ioctl call handling. This routine should return -ENOIOCTLCMD
166 if a command is not supported. The parameters that are passed to the ioctl
167 call are: watchdog_device, cmd and arg.
Wim Van Sebroeck43316042011-07-22 18:55:18 +0000168
169The 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 Sebroeck43316042011-07-22 18:55:18 +0000175* WDOG_DEV_OPEN: this status bit shows whether or not the watchdog device
176 was opened via /dev/watchdog.
177 (This bit should only be used by the WatchDog Timer Driver Core).
Wim Van Sebroeck017cf082011-07-22 18:58:54 +0000178* WDOG_ALLOW_RELEASE: this bit stores whether or not the magic close character
179 has been sent (so that we can support the magic close feature).
180 (This bit should only be used by the WatchDog Timer Driver Core).
Wim Van Sebroeck7e192b92011-07-22 18:59:17 +0000181* WDOG_NO_WAY_OUT: this bit stores the nowayout setting for the watchdog.
182 If this bit is set then the watchdog timer will not be able to stop.
Hans de Goedee907df32012-05-22 11:40:26 +0200183* WDOG_UNREGISTERED: this bit gets set by the WatchDog Timer Driver Core
184 after calling watchdog_unregister_device, and then checked before calling
185 any watchdog_ops, so that you can be sure that no operations (other then
186 unref) will get called after unregister, even if userspace still holds a
187 reference to /dev/watchdog
Wim Van Sebroeck017cf082011-07-22 18:58:54 +0000188
Wim Van Sebroeckff0b3cd2011-11-29 16:24:16 +0100189 To set the WDOG_NO_WAY_OUT status bit (before registering your watchdog
190 timer device) you can either:
191 * set it statically in your watchdog_device struct with
192 .status = WATCHDOG_NOWAYOUT_INIT_STATUS,
193 (this will set the value the same as CONFIG_WATCHDOG_NOWAYOUT) or
194 * use the following helper function:
195 static inline void watchdog_set_nowayout(struct watchdog_device *wdd, int nowayout)
196
Wim Van Sebroeck7e192b92011-07-22 18:59:17 +0000197Note: The WatchDog Timer Driver Core supports the magic close feature and
198the nowayout feature. To use the magic close feature you must set the
199WDIOF_MAGICCLOSE bit in the options field of the watchdog's info structure.
200The nowayout feature will overrule the magic close feature.
Wim Van Sebroeck43316042011-07-22 18:55:18 +0000201
202To get or set driver specific data the following two helper functions should be
203used:
204
205static inline void watchdog_set_drvdata(struct watchdog_device *wdd, void *data)
206static inline void *watchdog_get_drvdata(struct watchdog_device *wdd)
207
208The watchdog_set_drvdata function allows you to add driver specific data. The
209arguments of this function are the watchdog device where you want to add the
210driver specific data to and a pointer to the data itself.
211
212The watchdog_get_drvdata function allows you to retrieve driver specific data.
213The argument of this function is the watchdog device where you want to retrieve
Masanari Iidae1986522012-02-11 00:09:20 +0900214data from. The function returns the pointer to the driver specific data.