Commit 2deca7365582b7568dbdd2c3d9eef7ac17d41fd6

Authored by Devendra Naga
Committed by Wim Van Sebroeck
1 parent 5f2430f554

Documentation/watchdog: Fix a small typo

Signed-off-by: Devendra Naga <devendra.aaru@gmail.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

Showing 1 changed file with 1 additions and 1 deletions Inline Diff

Documentation/watchdog/watchdog-kernel-api.txt
1 The Linux WatchDog Timer Driver Core kernel API. 1 The Linux WatchDog Timer Driver Core kernel API.
2 =============================================== 2 ===============================================
3 Last reviewed: 16-Mar-2012 3 Last reviewed: 16-Mar-2012
4 4
5 Wim Van Sebroeck <wim@iguana.be> 5 Wim Van Sebroeck <wim@iguana.be>
6 6
7 Introduction 7 Introduction
8 ------------ 8 ------------
9 This document does not describe what a WatchDog Timer (WDT) Driver or Device is. 9 This document does not describe what a WatchDog Timer (WDT) Driver or Device is.
10 It also does not describe the API which can be used by user space to communicate 10 It also does not describe the API which can be used by user space to communicate
11 with a WatchDog Timer. If you want to know this then please read the following 11 with a WatchDog Timer. If you want to know this then please read the following
12 file: Documentation/watchdog/watchdog-api.txt . 12 file: Documentation/watchdog/watchdog-api.txt .
13 13
14 So what does this document describe? It describes the API that can be used by 14 So what does this document describe? It describes the API that can be used by
15 WatchDog Timer Drivers that want to use the WatchDog Timer Driver Core 15 WatchDog Timer Drivers that want to use the WatchDog Timer Driver Core
16 Framework. This framework provides all interfacing towards user space so that 16 Framework. This framework provides all interfacing towards user space so that
17 the same code does not have to be reproduced each time. This also means that 17 the same code does not have to be reproduced each time. This also means that
18 a watchdog timer driver then only needs to provide the different routines 18 a watchdog timer driver then only needs to provide the different routines
19 (operations) that control the watchdog timer (WDT). 19 (operations) that control the watchdog timer (WDT).
20 20
21 The API 21 The API
22 ------- 22 -------
23 Each watchdog timer driver that wants to use the WatchDog Timer Driver Core 23 Each watchdog timer driver that wants to use the WatchDog Timer Driver Core
24 must #include <linux/watchdog.h> (you would have to do this anyway when 24 must #include <linux/watchdog.h> (you would have to do this anyway when
25 writing a watchdog device driver). This include file contains following 25 writing a watchdog device driver). This include file contains following
26 register/unregister routines: 26 register/unregister routines:
27 27
28 extern int watchdog_register_device(struct watchdog_device *); 28 extern int watchdog_register_device(struct watchdog_device *);
29 extern void watchdog_unregister_device(struct watchdog_device *); 29 extern void watchdog_unregister_device(struct watchdog_device *);
30 30
31 The watchdog_register_device routine registers a watchdog timer device. 31 The watchdog_register_device routine registers a watchdog timer device.
32 The parameter of this routine is a pointer to a watchdog_device structure. 32 The parameter of this routine is a pointer to a watchdog_device structure.
33 This routine returns zero on success and a negative errno code for failure. 33 This routine returns zero on success and a negative errno code for failure.
34 34
35 The watchdog_unregister_device routine deregisters a registered watchdog timer 35 The watchdog_unregister_device routine deregisters a registered watchdog timer
36 device. The parameter of this routine is the pointer to the registered 36 device. The parameter of this routine is the pointer to the registered
37 watchdog_device structure. 37 watchdog_device structure.
38 38
39 The watchdog device structure looks like this: 39 The watchdog device structure looks like this:
40 40
41 struct watchdog_device { 41 struct watchdog_device {
42 const struct watchdog_info *info; 42 const struct watchdog_info *info;
43 const struct watchdog_ops *ops; 43 const struct watchdog_ops *ops;
44 unsigned int bootstatus; 44 unsigned int bootstatus;
45 unsigned int timeout; 45 unsigned int timeout;
46 unsigned int min_timeout; 46 unsigned int min_timeout;
47 unsigned int max_timeout; 47 unsigned int max_timeout;
48 void *driver_data; 48 void *driver_data;
49 unsigned long status; 49 unsigned long status;
50 }; 50 };
51 51
52 It contains following fields: 52 It contains following fields:
53 * info: a pointer to a watchdog_info structure. This structure gives some 53 * info: a pointer to a watchdog_info structure. This structure gives some
54 additional information about the watchdog timer itself. (Like it's unique name) 54 additional information about the watchdog timer itself. (Like it's unique name)
55 * ops: a pointer to the list of watchdog operations that the watchdog supports. 55 * ops: a pointer to the list of watchdog operations that the watchdog supports.
56 * timeout: the watchdog timer's timeout value (in seconds). 56 * timeout: the watchdog timer's timeout value (in seconds).
57 * min_timeout: the watchdog timer's minimum timeout value (in seconds). 57 * min_timeout: the watchdog timer's minimum timeout value (in seconds).
58 * max_timeout: the watchdog timer's maximum timeout value (in seconds). 58 * max_timeout: the watchdog timer's maximum timeout value (in seconds).
59 * bootstatus: status of the device after booting (reported with watchdog 59 * bootstatus: status of the device after booting (reported with watchdog
60 WDIOF_* status bits). 60 WDIOF_* status bits).
61 * driver_data: a pointer to the drivers private data of a watchdog device. 61 * driver_data: a pointer to the drivers private data of a watchdog device.
62 This data should only be accessed via the watchdog_set_drvadata and 62 This data should only be accessed via the watchdog_set_drvdata and
63 watchdog_get_drvdata routines. 63 watchdog_get_drvdata routines.
64 * status: this field contains a number of status bits that give extra 64 * status: this field contains a number of status bits that give extra
65 information about the status of the device (Like: is the watchdog timer 65 information about the status of the device (Like: is the watchdog timer
66 running/active, is the nowayout bit set, is the device opened via 66 running/active, is the nowayout bit set, is the device opened via
67 the /dev/watchdog interface or not, ...). 67 the /dev/watchdog interface or not, ...).
68 68
69 The list of watchdog operations is defined as: 69 The list of watchdog operations is defined as:
70 70
71 struct watchdog_ops { 71 struct watchdog_ops {
72 struct module *owner; 72 struct module *owner;
73 /* mandatory operations */ 73 /* mandatory operations */
74 int (*start)(struct watchdog_device *); 74 int (*start)(struct watchdog_device *);
75 int (*stop)(struct watchdog_device *); 75 int (*stop)(struct watchdog_device *);
76 /* optional operations */ 76 /* optional operations */
77 int (*ping)(struct watchdog_device *); 77 int (*ping)(struct watchdog_device *);
78 unsigned int (*status)(struct watchdog_device *); 78 unsigned int (*status)(struct watchdog_device *);
79 int (*set_timeout)(struct watchdog_device *, unsigned int); 79 int (*set_timeout)(struct watchdog_device *, unsigned int);
80 unsigned int (*get_timeleft)(struct watchdog_device *); 80 unsigned int (*get_timeleft)(struct watchdog_device *);
81 long (*ioctl)(struct watchdog_device *, unsigned int, unsigned long); 81 long (*ioctl)(struct watchdog_device *, unsigned int, unsigned long);
82 }; 82 };
83 83
84 It is important that you first define the module owner of the watchdog timer 84 It is important that you first define the module owner of the watchdog timer
85 driver's operations. This module owner will be used to lock the module when 85 driver's operations. This module owner will be used to lock the module when
86 the watchdog is active. (This to avoid a system crash when you unload the 86 the watchdog is active. (This to avoid a system crash when you unload the
87 module and /dev/watchdog is still open). 87 module and /dev/watchdog is still open).
88 Some operations are mandatory and some are optional. The mandatory operations 88 Some operations are mandatory and some are optional. The mandatory operations
89 are: 89 are:
90 * start: this is a pointer to the routine that starts the watchdog timer 90 * start: this is a pointer to the routine that starts the watchdog timer
91 device. 91 device.
92 The routine needs a pointer to the watchdog timer device structure as a 92 The routine needs a pointer to the watchdog timer device structure as a
93 parameter. It returns zero on success or a negative errno code for failure. 93 parameter. It returns zero on success or a negative errno code for failure.
94 * stop: with this routine the watchdog timer device is being stopped. 94 * stop: with this routine the watchdog timer device is being stopped.
95 The routine needs a pointer to the watchdog timer device structure as a 95 The routine needs a pointer to the watchdog timer device structure as a
96 parameter. It returns zero on success or a negative errno code for failure. 96 parameter. It returns zero on success or a negative errno code for failure.
97 Some watchdog timer hardware can only be started and not be stopped. The 97 Some watchdog timer hardware can only be started and not be stopped. The
98 driver supporting this hardware needs to make sure that a start and stop 98 driver supporting this hardware needs to make sure that a start and stop
99 routine is being provided. This can be done by using a timer in the driver 99 routine is being provided. This can be done by using a timer in the driver
100 that regularly sends a keepalive ping to the watchdog timer hardware. 100 that regularly sends a keepalive ping to the watchdog timer hardware.
101 101
102 Not all watchdog timer hardware supports the same functionality. That's why 102 Not all watchdog timer hardware supports the same functionality. That's why
103 all other routines/operations are optional. They only need to be provided if 103 all other routines/operations are optional. They only need to be provided if
104 they are supported. These optional routines/operations are: 104 they are supported. These optional routines/operations are:
105 * ping: this is the routine that sends a keepalive ping to the watchdog timer 105 * ping: this is the routine that sends a keepalive ping to the watchdog timer
106 hardware. 106 hardware.
107 The routine needs a pointer to the watchdog timer device structure as a 107 The routine needs a pointer to the watchdog timer device structure as a
108 parameter. It returns zero on success or a negative errno code for failure. 108 parameter. It returns zero on success or a negative errno code for failure.
109 Most hardware that does not support this as a separate function uses the 109 Most hardware that does not support this as a separate function uses the
110 start function to restart the watchdog timer hardware. And that's also what 110 start function to restart the watchdog timer hardware. And that's also what
111 the watchdog timer driver core does: to send a keepalive ping to the watchdog 111 the watchdog timer driver core does: to send a keepalive ping to the watchdog
112 timer hardware it will either use the ping operation (when available) or the 112 timer hardware it will either use the ping operation (when available) or the
113 start operation (when the ping operation is not available). 113 start operation (when the ping operation is not available).
114 (Note: the WDIOC_KEEPALIVE ioctl call will only be active when the 114 (Note: the WDIOC_KEEPALIVE ioctl call will only be active when the
115 WDIOF_KEEPALIVEPING bit has been set in the option field on the watchdog's 115 WDIOF_KEEPALIVEPING bit has been set in the option field on the watchdog's
116 info structure). 116 info structure).
117 * status: this routine checks the status of the watchdog timer device. The 117 * status: this routine checks the status of the watchdog timer device. The
118 status of the device is reported with watchdog WDIOF_* status flags/bits. 118 status of the device is reported with watchdog WDIOF_* status flags/bits.
119 * set_timeout: this routine checks and changes the timeout of the watchdog 119 * set_timeout: this routine checks and changes the timeout of the watchdog
120 timer device. It returns 0 on success, -EINVAL for "parameter out of range" 120 timer device. It returns 0 on success, -EINVAL for "parameter out of range"
121 and -EIO for "could not write value to the watchdog". On success this 121 and -EIO for "could not write value to the watchdog". On success this
122 routine should set the timeout value of the watchdog_device to the 122 routine should set the timeout value of the watchdog_device to the
123 achieved timeout value (which may be different from the requested one 123 achieved timeout value (which may be different from the requested one
124 because the watchdog does not necessarily has a 1 second resolution). 124 because the watchdog does not necessarily has a 1 second resolution).
125 (Note: the WDIOF_SETTIMEOUT needs to be set in the options field of the 125 (Note: the WDIOF_SETTIMEOUT needs to be set in the options field of the
126 watchdog's info structure). 126 watchdog's info structure).
127 * get_timeleft: this routines returns the time that's left before a reset. 127 * get_timeleft: this routines returns the time that's left before a reset.
128 * ioctl: if this routine is present then it will be called first before we do 128 * ioctl: if this routine is present then it will be called first before we do
129 our own internal ioctl call handling. This routine should return -ENOIOCTLCMD 129 our own internal ioctl call handling. This routine should return -ENOIOCTLCMD
130 if a command is not supported. The parameters that are passed to the ioctl 130 if a command is not supported. The parameters that are passed to the ioctl
131 call are: watchdog_device, cmd and arg. 131 call are: watchdog_device, cmd and arg.
132 132
133 The status bits should (preferably) be set with the set_bit and clear_bit alike 133 The status bits should (preferably) be set with the set_bit and clear_bit alike
134 bit-operations. The status bits that are defined are: 134 bit-operations. The status bits that are defined are:
135 * WDOG_ACTIVE: this status bit indicates whether or not a watchdog timer device 135 * WDOG_ACTIVE: this status bit indicates whether or not a watchdog timer device
136 is active or not. When the watchdog is active after booting, then you should 136 is active or not. When the watchdog is active after booting, then you should
137 set this status bit (Note: when you register the watchdog timer device with 137 set this status bit (Note: when you register the watchdog timer device with
138 this bit set, then opening /dev/watchdog will skip the start operation) 138 this bit set, then opening /dev/watchdog will skip the start operation)
139 * WDOG_DEV_OPEN: this status bit shows whether or not the watchdog device 139 * WDOG_DEV_OPEN: this status bit shows whether or not the watchdog device
140 was opened via /dev/watchdog. 140 was opened via /dev/watchdog.
141 (This bit should only be used by the WatchDog Timer Driver Core). 141 (This bit should only be used by the WatchDog Timer Driver Core).
142 * WDOG_ALLOW_RELEASE: this bit stores whether or not the magic close character 142 * WDOG_ALLOW_RELEASE: this bit stores whether or not the magic close character
143 has been sent (so that we can support the magic close feature). 143 has been sent (so that we can support the magic close feature).
144 (This bit should only be used by the WatchDog Timer Driver Core). 144 (This bit should only be used by the WatchDog Timer Driver Core).
145 * WDOG_NO_WAY_OUT: this bit stores the nowayout setting for the watchdog. 145 * WDOG_NO_WAY_OUT: this bit stores the nowayout setting for the watchdog.
146 If this bit is set then the watchdog timer will not be able to stop. 146 If this bit is set then the watchdog timer will not be able to stop.
147 147
148 To set the WDOG_NO_WAY_OUT status bit (before registering your watchdog 148 To set the WDOG_NO_WAY_OUT status bit (before registering your watchdog
149 timer device) you can either: 149 timer device) you can either:
150 * set it statically in your watchdog_device struct with 150 * set it statically in your watchdog_device struct with
151 .status = WATCHDOG_NOWAYOUT_INIT_STATUS, 151 .status = WATCHDOG_NOWAYOUT_INIT_STATUS,
152 (this will set the value the same as CONFIG_WATCHDOG_NOWAYOUT) or 152 (this will set the value the same as CONFIG_WATCHDOG_NOWAYOUT) or
153 * use the following helper function: 153 * use the following helper function:
154 static inline void watchdog_set_nowayout(struct watchdog_device *wdd, int nowayout) 154 static inline void watchdog_set_nowayout(struct watchdog_device *wdd, int nowayout)
155 155
156 Note: The WatchDog Timer Driver Core supports the magic close feature and 156 Note: The WatchDog Timer Driver Core supports the magic close feature and
157 the nowayout feature. To use the magic close feature you must set the 157 the nowayout feature. To use the magic close feature you must set the
158 WDIOF_MAGICCLOSE bit in the options field of the watchdog's info structure. 158 WDIOF_MAGICCLOSE bit in the options field of the watchdog's info structure.
159 The nowayout feature will overrule the magic close feature. 159 The nowayout feature will overrule the magic close feature.
160 160
161 To get or set driver specific data the following two helper functions should be 161 To get or set driver specific data the following two helper functions should be
162 used: 162 used:
163 163
164 static inline void watchdog_set_drvdata(struct watchdog_device *wdd, void *data) 164 static inline void watchdog_set_drvdata(struct watchdog_device *wdd, void *data)
165 static inline void *watchdog_get_drvdata(struct watchdog_device *wdd) 165 static inline void *watchdog_get_drvdata(struct watchdog_device *wdd)
166 166
167 The watchdog_set_drvdata function allows you to add driver specific data. The 167 The watchdog_set_drvdata function allows you to add driver specific data. The
168 arguments of this function are the watchdog device where you want to add the 168 arguments of this function are the watchdog device where you want to add the
169 driver specific data to and a pointer to the data itself. 169 driver specific data to and a pointer to the data itself.
170 170
171 The watchdog_get_drvdata function allows you to retrieve driver specific data. 171 The watchdog_get_drvdata function allows you to retrieve driver specific data.
172 The argument of this function is the watchdog device where you want to retrieve 172 The argument of this function is the watchdog device where you want to retrieve
173 data from. The function returns the pointer to the driver specific data. 173 data from. The function returns the pointer to the driver specific data.
174 174