File: /usr/src/linux/drivers/char/sbc60xxwdt.c
1 /*
2 * 60xx Single Board Computer Watchdog Timer driver for Linux 2.2.x
3 *
4 * Based on acquirewdt.c by Alan Cox.
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
10 *
11 * The author does NOT admit liability nor provide warranty for
12 * any of this software. This material is provided "AS-IS" in
13 * the hope that it may be useful for others.
14 *
15 * (c) Copyright 2000 Jakob Oestergaard <jakob@ostenfeld.dk>
16 *
17 * 12/4 - 2000 [Initial revision]
18 * 25/4 - 2000 Added /dev/watchdog support
19 * 09/5 - 2001 [smj@oro.net] fixed fop_write to "return 1" on success
20 *
21 *
22 * Theory of operation:
23 * A Watchdog Timer (WDT) is a hardware circuit that can
24 * reset the computer system in case of a software fault.
25 * You probably knew that already.
26 *
27 * Usually a userspace daemon will notify the kernel WDT driver
28 * via the /proc/watchdog special device file that userspace is
29 * still alive, at regular intervals. When such a notification
30 * occurs, the driver will usually tell the hardware watchdog
31 * that everything is in order, and that the watchdog should wait
32 * for yet another little while to reset the system.
33 * If userspace fails (RAM error, kernel bug, whatever), the
34 * notifications cease to occur, and the hardware watchdog will
35 * reset the system (causing a reboot) after the timeout occurs.
36 *
37 * This WDT driver is different from the other Linux WDT
38 * drivers in several ways:
39 * *) The driver will ping the watchdog by itself, because this
40 * particular WDT has a very short timeout (one second) and it
41 * would be insane to count on any userspace daemon always
42 * getting scheduled within that time frame.
43 * *) This driver expects the userspace daemon to send a specific
44 * character code ('V') to /dev/watchdog before closing the
45 * /dev/watchdog file. If the userspace daemon closes the file
46 * without sending this special character, the driver will assume
47 * that the daemon (and userspace in general) died, and will
48 * stop pinging the WDT without disabling it first. This will
49 * cause a reboot.
50 *
51 * Why `V' ? Well, `V' is the character in ASCII for the value 86,
52 * and we all know that 86 is _the_ most random number in the universe.
53 * Therefore it is the letter that has the slightest chance of occuring
54 * by chance, when the system becomes corrupted.
55 *
56 */
57
58 #include <linux/module.h>
59 #include <linux/version.h>
60 #include <linux/types.h>
61 #include <linux/errno.h>
62 #include <linux/kernel.h>
63 #include <linux/timer.h>
64 #include <linux/sched.h>
65 #include <linux/miscdevice.h>
66 #include <linux/watchdog.h>
67 #include <linux/slab.h>
68 #include <linux/ioport.h>
69 #include <linux/fcntl.h>
70 #include <linux/smp_lock.h>
71 #include <asm/io.h>
72 #include <asm/uaccess.h>
73 #include <asm/system.h>
74 #include <linux/notifier.h>
75 #include <linux/reboot.h>
76 #include <linux/init.h>
77
78 #define OUR_NAME "sbc60xxwdt"
79
80 /*
81 * You must set these - The driver cannot probe for the settings
82 */
83
84 #define WDT_STOP 0x45
85 #define WDT_START 0x443
86
87 /*
88 * The 60xx board can use watchdog timeout values from one second
89 * to several minutes. The default is one second, so if we reset
90 * the watchdog every ~250ms we should be safe.
91 */
92
93 #define WDT_INTERVAL (HZ/4+1)
94
95 /*
96 * We must not require too good response from the userspace daemon.
97 * Here we require the userspace daemon to send us a heartbeat
98 * char to /dev/watchdog every 10 seconds.
99 * If the daemon pulses us every 5 seconds, we can still afford
100 * a 5 second scheduling delay on the (high priority) daemon. That
101 * should be sufficient for a box under any load.
102 */
103
104 #define WDT_HEARTBEAT (HZ * 10)
105
106 static void wdt_timer_ping(unsigned long);
107 static struct timer_list timer;
108 static unsigned long next_heartbeat;
109 static int wdt_is_open;
110 static int wdt_expect_close;
111
112 /*
113 * Whack the dog
114 */
115
116 static void wdt_timer_ping(unsigned long data)
117 {
118 /* If we got a heartbeat pulse within the WDT_US_INTERVAL
119 * we agree to ping the WDT
120 */
121 if(time_before(jiffies, next_heartbeat))
122 {
123 /* Ping the WDT by reading from WDT_START */
124 inb_p(WDT_START);
125 /* Re-set the timer interval */
126 timer.expires = jiffies + WDT_INTERVAL;
127 add_timer(&timer);
128 } else {
129 printk(OUR_NAME ": Heartbeat lost! Will not ping the watchdog\n");
130 }
131 }
132
133 /*
134 * Utility routines
135 */
136
137 static void wdt_startup(void)
138 {
139 next_heartbeat = jiffies + WDT_HEARTBEAT;
140
141 /* Start the timer */
142 timer.expires = jiffies + WDT_INTERVAL;
143 add_timer(&timer);
144 printk(OUR_NAME ": Watchdog timer is now enabled.\n");
145 }
146
147 static void wdt_turnoff(void)
148 {
149 /* Stop the timer */
150 del_timer(&timer);
151 inb_p(WDT_STOP);
152 printk(OUR_NAME ": Watchdog timer is now disabled...\n");
153 }
154
155
156 /*
157 * /dev/watchdog handling
158 */
159
160 static ssize_t fop_write(struct file * file, const char * buf, size_t count, loff_t * ppos)
161 {
162 /* We can't seek */
163 if(ppos != &file->f_pos)
164 return -ESPIPE;
165
166 /* See if we got the magic character */
167 if(count)
168 {
169 size_t ofs;
170
171 /* note: just in case someone wrote the magic character
172 * five months ago... */
173 wdt_expect_close = 0;
174
175 /* now scan */
176 for(ofs = 0; ofs != count; ofs++)
177 {
178 char c;
179 if(get_user(c, buf+ofs))
180 return -EFAULT;
181 if(c == 'V')
182 wdt_expect_close = 1;
183 }
184 /* Well, anyhow someone wrote to us, we should return that favour */
185 next_heartbeat = jiffies + WDT_HEARTBEAT;
186 return 1;
187 }
188 return 0;
189 }
190
191 static ssize_t fop_read(struct file * file, char * buf, size_t count, loff_t * ppos)
192 {
193 /* No can do */
194 return -EINVAL;
195 }
196
197 static int fop_open(struct inode * inode, struct file * file)
198 {
199 switch(MINOR(inode->i_rdev))
200 {
201 case WATCHDOG_MINOR:
202 /* Just in case we're already talking to someone... */
203 if(wdt_is_open)
204 return -EBUSY;
205 /* Good, fire up the show */
206 wdt_is_open = 1;
207 wdt_startup();
208 return 0;
209
210 default:
211 return -ENODEV;
212 }
213 }
214
215 static int fop_close(struct inode * inode, struct file * file)
216 {
217 lock_kernel();
218 if(MINOR(inode->i_rdev) == WATCHDOG_MINOR)
219 {
220 if(wdt_expect_close)
221 wdt_turnoff();
222 else {
223 del_timer(&timer);
224 printk(OUR_NAME ": device file closed unexpectedly. Will not stop the WDT!\n");
225 }
226 }
227 wdt_is_open = 0;
228 unlock_kernel();
229 return 0;
230 }
231
232 static int fop_ioctl(struct inode *inode, struct file *file, unsigned int cmd,
233 unsigned long arg)
234 {
235 static struct watchdog_info ident=
236 {
237 0,
238 1,
239 "SB60xx"
240 };
241
242 switch(cmd)
243 {
244 default:
245 return -ENOTTY;
246 case WDIOC_GETSUPPORT:
247 return copy_to_user((struct watchdog_info *)arg, &ident, sizeof(ident))?-EFAULT:0;
248 case WDIOC_KEEPALIVE:
249 next_heartbeat = jiffies + WDT_HEARTBEAT;
250 return 0;
251 }
252 }
253
254 static struct file_operations wdt_fops = {
255 owner: THIS_MODULE,
256 llseek: no_llseek,
257 read: fop_read,
258 write: fop_write,
259 open: fop_open,
260 release: fop_close,
261 ioctl: fop_ioctl
262 };
263
264 static struct miscdevice wdt_miscdev = {
265 WATCHDOG_MINOR,
266 "watchdog",
267 &wdt_fops
268 };
269
270 /*
271 * Notifier for system down
272 */
273
274 static int wdt_notify_sys(struct notifier_block *this, unsigned long code,
275 void *unused)
276 {
277 if(code==SYS_DOWN || code==SYS_HALT)
278 wdt_turnoff();
279 return NOTIFY_DONE;
280 }
281
282 /*
283 * The WDT needs to learn about soft shutdowns in order to
284 * turn the timebomb registers off.
285 */
286
287 static struct notifier_block wdt_notifier=
288 {
289 wdt_notify_sys,
290 0,
291 0
292 };
293
294 static void __exit sbc60xxwdt_unload(void)
295 {
296 wdt_turnoff();
297
298 /* Deregister */
299 misc_deregister(&wdt_miscdev);
300
301 unregister_reboot_notifier(&wdt_notifier);
302 release_region(WDT_START,1);
303 release_region(WDT_STOP,1);
304 }
305
306 static int __init sbc60xxwdt_init(void)
307 {
308 int rc = -EBUSY;
309
310 if (!request_region(WDT_STOP, 1, "SBC 60XX WDT"))
311 goto err_out;
312 if (!request_region(WDT_START, 1, "SBC 60XX WDT"))
313 goto err_out_region1;
314
315 init_timer(&timer);
316 timer.function = wdt_timer_ping;
317 timer.data = 0;
318
319 rc = misc_register(&wdt_miscdev);
320 if (rc)
321 goto err_out_region2;
322
323 rc = register_reboot_notifier(&wdt_notifier);
324 if (rc)
325 goto err_out_miscdev;
326
327 printk(KERN_INFO OUR_NAME ": WDT driver for 60XX single board computer initialised.\n");
328
329 return 0;
330
331 err_out_miscdev:
332 misc_deregister(&wdt_miscdev);
333 err_out_region2:
334 release_region(WDT_START,1);
335 err_out_region1:
336 release_region(WDT_STOP,1);
337 err_out:
338 return rc;
339 }
340
341 module_init(sbc60xxwdt_init);
342 module_exit(sbc60xxwdt_unload);
343
344 MODULE_LICENSE("GPL");
345 EXPORT_NO_SYMBOLS;
346