1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3  *	watchdog_dev.c
4  *
5  *	(c) Copyright 2008-2011 Alan Cox <alan@lxorguk.ukuu.org.uk>,
6  *						All Rights Reserved.
7  *
8  *	(c) Copyright 2008-2011 Wim Van Sebroeck <wim@iguana.be>.
9  *
10  *
11  *	This source code is part of the generic code that can be used
12  *	by all the watchdog timer drivers.
13  *
14  *	This part of the generic code takes care of the following
15  *	misc device: /dev/watchdog.
16  *
17  *	Based on source code of the following authors:
18  *	  Matt Domsch <Matt_Domsch@dell.com>,
19  *	  Rob Radez <rob@osinvestor.com>,
20  *	  Rusty Lynch <rusty@linux.co.intel.com>
21  *	  Satyam Sharma <satyam@infradead.org>
22  *	  Randy Dunlap <randy.dunlap@oracle.com>
23  *
24  *	Neither Alan Cox, CymruNet Ltd., Wim Van Sebroeck nor Iguana vzw.
25  *	admit liability nor provide warranty for any of this software.
26  *	This material is provided "AS-IS" and at no charge.
27  */
28 
29 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
30 
31 #include <linux/cdev.h>		/* For character device */
32 #include <linux/errno.h>	/* For the -ENODEV/... values */
33 #include <linux/fs.h>		/* For file operations */
34 #include <linux/init.h>		/* For __init/__exit/... */
35 #include <linux/hrtimer.h>	/* For hrtimers */
36 #include <linux/kernel.h>	/* For printk/panic/... */
37 #include <linux/kthread.h>	/* For kthread_work */
38 #include <linux/miscdevice.h>	/* For handling misc devices */
39 #include <linux/module.h>	/* For module stuff/... */
40 #include <linux/mutex.h>	/* For mutexes */
41 #include <linux/slab.h>		/* For memory functions */
42 #include <linux/types.h>	/* For standard types (like size_t) */
43 #include <linux/watchdog.h>	/* For watchdog specific items */
44 #include <linux/uaccess.h>	/* For copy_to_user/put_user/... */
45 
46 #include <uapi/linux/sched/types.h>	/* For struct sched_param */
47 
48 #include "watchdog_core.h"
49 #include "watchdog_pretimeout.h"
50 
51 /*
52  * struct watchdog_core_data - watchdog core internal data
53  * @dev:	The watchdog's internal device
54  * @cdev:	The watchdog's Character device.
55  * @wdd:	Pointer to watchdog device.
56  * @lock:	Lock for watchdog core.
57  * @status:	Watchdog core internal status bits.
58  */
59 struct watchdog_core_data {
60 	struct device dev;
61 	struct cdev cdev;
62 	struct watchdog_device *wdd;
63 	struct mutex lock;
64 	ktime_t last_keepalive;
65 	ktime_t last_hw_keepalive;
66 	ktime_t open_deadline;
67 	struct hrtimer timer;
68 	struct kthread_work work;
69 	unsigned long status;		/* Internal status bits */
70 #define _WDOG_DEV_OPEN		0	/* Opened ? */
71 #define _WDOG_ALLOW_RELEASE	1	/* Did we receive the magic char ? */
72 #define _WDOG_KEEPALIVE		2	/* Did we receive a keepalive ? */
73 };
74 
75 /* the dev_t structure to store the dynamically allocated watchdog devices */
76 static dev_t watchdog_devt;
77 /* Reference to watchdog device behind /dev/watchdog */
78 static struct watchdog_core_data *old_wd_data;
79 
80 static struct kthread_worker *watchdog_kworker;
81 
82 static bool handle_boot_enabled =
83 	IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED);
84 
85 static unsigned open_timeout = CONFIG_WATCHDOG_OPEN_TIMEOUT;
86 
87 static bool watchdog_past_open_deadline(struct watchdog_core_data *data)
88 {
89 	return ktime_after(ktime_get(), data->open_deadline);
90 }
91 
92 static void watchdog_set_open_deadline(struct watchdog_core_data *data)
93 {
94 	data->open_deadline = open_timeout ?
95 		ktime_get() + ktime_set(open_timeout, 0) : KTIME_MAX;
96 }
97 
98 static inline bool watchdog_need_worker(struct watchdog_device *wdd)
99 {
100 	/* All variables in milli-seconds */
101 	unsigned int hm = wdd->max_hw_heartbeat_ms;
102 	unsigned int t = wdd->timeout * 1000;
103 
104 	/*
105 	 * A worker to generate heartbeat requests is needed if all of the
106 	 * following conditions are true.
107 	 * - Userspace activated the watchdog.
108 	 * - The driver provided a value for the maximum hardware timeout, and
109 	 *   thus is aware that the framework supports generating heartbeat
110 	 *   requests.
111 	 * - Userspace requests a longer timeout than the hardware can handle.
112 	 *
113 	 * Alternatively, if userspace has not opened the watchdog
114 	 * device, we take care of feeding the watchdog if it is
115 	 * running.
116 	 */
117 	return (hm && watchdog_active(wdd) && t > hm) ||
118 		(t && !watchdog_active(wdd) && watchdog_hw_running(wdd));
119 }
120 
121 static ktime_t watchdog_next_keepalive(struct watchdog_device *wdd)
122 {
123 	struct watchdog_core_data *wd_data = wdd->wd_data;
124 	unsigned int timeout_ms = wdd->timeout * 1000;
125 	ktime_t keepalive_interval;
126 	ktime_t last_heartbeat, latest_heartbeat;
127 	ktime_t virt_timeout;
128 	unsigned int hw_heartbeat_ms;
129 
130 	if (watchdog_active(wdd))
131 		virt_timeout = ktime_add(wd_data->last_keepalive,
132 					 ms_to_ktime(timeout_ms));
133 	else
134 		virt_timeout = wd_data->open_deadline;
135 
136 	hw_heartbeat_ms = min_not_zero(timeout_ms, wdd->max_hw_heartbeat_ms);
137 	keepalive_interval = ms_to_ktime(hw_heartbeat_ms / 2);
138 
139 	/*
140 	 * To ensure that the watchdog times out wdd->timeout seconds
141 	 * after the most recent ping from userspace, the last
142 	 * worker ping has to come in hw_heartbeat_ms before this timeout.
143 	 */
144 	last_heartbeat = ktime_sub(virt_timeout, ms_to_ktime(hw_heartbeat_ms));
145 	latest_heartbeat = ktime_sub(last_heartbeat, ktime_get());
146 	if (ktime_before(latest_heartbeat, keepalive_interval))
147 		return latest_heartbeat;
148 	return keepalive_interval;
149 }
150 
151 static inline void watchdog_update_worker(struct watchdog_device *wdd)
152 {
153 	struct watchdog_core_data *wd_data = wdd->wd_data;
154 
155 	if (watchdog_need_worker(wdd)) {
156 		ktime_t t = watchdog_next_keepalive(wdd);
157 
158 		if (t > 0)
159 			hrtimer_start(&wd_data->timer, t,
160 				      HRTIMER_MODE_REL_HARD);
161 	} else {
162 		hrtimer_cancel(&wd_data->timer);
163 	}
164 }
165 
166 static int __watchdog_ping(struct watchdog_device *wdd)
167 {
168 	struct watchdog_core_data *wd_data = wdd->wd_data;
169 	ktime_t earliest_keepalive, now;
170 	int err;
171 
172 	earliest_keepalive = ktime_add(wd_data->last_hw_keepalive,
173 				       ms_to_ktime(wdd->min_hw_heartbeat_ms));
174 	now = ktime_get();
175 
176 	if (ktime_after(earliest_keepalive, now)) {
177 		hrtimer_start(&wd_data->timer,
178 			      ktime_sub(earliest_keepalive, now),
179 			      HRTIMER_MODE_REL_HARD);
180 		return 0;
181 	}
182 
183 	wd_data->last_hw_keepalive = now;
184 
185 	if (wdd->ops->ping)
186 		err = wdd->ops->ping(wdd);  /* ping the watchdog */
187 	else
188 		err = wdd->ops->start(wdd); /* restart watchdog */
189 
190 	watchdog_update_worker(wdd);
191 
192 	return err;
193 }
194 
195 /*
196  *	watchdog_ping: ping the watchdog.
197  *	@wdd: the watchdog device to ping
198  *
199  *	The caller must hold wd_data->lock.
200  *
201  *	If the watchdog has no own ping operation then it needs to be
202  *	restarted via the start operation. This wrapper function does
203  *	exactly that.
204  *	We only ping when the watchdog device is running.
205  */
206 
207 static int watchdog_ping(struct watchdog_device *wdd)
208 {
209 	struct watchdog_core_data *wd_data = wdd->wd_data;
210 
211 	if (!watchdog_active(wdd) && !watchdog_hw_running(wdd))
212 		return 0;
213 
214 	set_bit(_WDOG_KEEPALIVE, &wd_data->status);
215 
216 	wd_data->last_keepalive = ktime_get();
217 	return __watchdog_ping(wdd);
218 }
219 
220 static bool watchdog_worker_should_ping(struct watchdog_core_data *wd_data)
221 {
222 	struct watchdog_device *wdd = wd_data->wdd;
223 
224 	if (!wdd)
225 		return false;
226 
227 	if (watchdog_active(wdd))
228 		return true;
229 
230 	return watchdog_hw_running(wdd) && !watchdog_past_open_deadline(wd_data);
231 }
232 
233 static void watchdog_ping_work(struct kthread_work *work)
234 {
235 	struct watchdog_core_data *wd_data;
236 
237 	wd_data = container_of(work, struct watchdog_core_data, work);
238 
239 	mutex_lock(&wd_data->lock);
240 	if (watchdog_worker_should_ping(wd_data))
241 		__watchdog_ping(wd_data->wdd);
242 	mutex_unlock(&wd_data->lock);
243 }
244 
245 static enum hrtimer_restart watchdog_timer_expired(struct hrtimer *timer)
246 {
247 	struct watchdog_core_data *wd_data;
248 
249 	wd_data = container_of(timer, struct watchdog_core_data, timer);
250 
251 	kthread_queue_work(watchdog_kworker, &wd_data->work);
252 	return HRTIMER_NORESTART;
253 }
254 
255 /*
256  *	watchdog_start: wrapper to start the watchdog.
257  *	@wdd: the watchdog device to start
258  *
259  *	The caller must hold wd_data->lock.
260  *
261  *	Start the watchdog if it is not active and mark it active.
262  *	This function returns zero on success or a negative errno code for
263  *	failure.
264  */
265 
266 static int watchdog_start(struct watchdog_device *wdd)
267 {
268 	struct watchdog_core_data *wd_data = wdd->wd_data;
269 	ktime_t started_at;
270 	int err;
271 
272 	if (watchdog_active(wdd))
273 		return 0;
274 
275 	set_bit(_WDOG_KEEPALIVE, &wd_data->status);
276 
277 	started_at = ktime_get();
278 	if (watchdog_hw_running(wdd) && wdd->ops->ping) {
279 		err = __watchdog_ping(wdd);
280 		if (err == 0)
281 			set_bit(WDOG_ACTIVE, &wdd->status);
282 	} else {
283 		err = wdd->ops->start(wdd);
284 		if (err == 0) {
285 			set_bit(WDOG_ACTIVE, &wdd->status);
286 			wd_data->last_keepalive = started_at;
287 			wd_data->last_hw_keepalive = started_at;
288 			watchdog_update_worker(wdd);
289 		}
290 	}
291 
292 	return err;
293 }
294 
295 /*
296  *	watchdog_stop: wrapper to stop the watchdog.
297  *	@wdd: the watchdog device to stop
298  *
299  *	The caller must hold wd_data->lock.
300  *
301  *	Stop the watchdog if it is still active and unmark it active.
302  *	This function returns zero on success or a negative errno code for
303  *	failure.
304  *	If the 'nowayout' feature was set, the watchdog cannot be stopped.
305  */
306 
307 static int watchdog_stop(struct watchdog_device *wdd)
308 {
309 	int err = 0;
310 
311 	if (!watchdog_active(wdd))
312 		return 0;
313 
314 	if (test_bit(WDOG_NO_WAY_OUT, &wdd->status)) {
315 		pr_info("watchdog%d: nowayout prevents watchdog being stopped!\n",
316 			wdd->id);
317 		return -EBUSY;
318 	}
319 
320 	if (wdd->ops->stop) {
321 		clear_bit(WDOG_HW_RUNNING, &wdd->status);
322 		err = wdd->ops->stop(wdd);
323 	} else {
324 		set_bit(WDOG_HW_RUNNING, &wdd->status);
325 	}
326 
327 	if (err == 0) {
328 		clear_bit(WDOG_ACTIVE, &wdd->status);
329 		watchdog_update_worker(wdd);
330 	}
331 
332 	return err;
333 }
334 
335 /*
336  *	watchdog_get_status: wrapper to get the watchdog status
337  *	@wdd: the watchdog device to get the status from
338  *
339  *	The caller must hold wd_data->lock.
340  *
341  *	Get the watchdog's status flags.
342  */
343 
344 static unsigned int watchdog_get_status(struct watchdog_device *wdd)
345 {
346 	struct watchdog_core_data *wd_data = wdd->wd_data;
347 	unsigned int status;
348 
349 	if (wdd->ops->status)
350 		status = wdd->ops->status(wdd);
351 	else
352 		status = wdd->bootstatus & (WDIOF_CARDRESET |
353 					    WDIOF_OVERHEAT |
354 					    WDIOF_FANFAULT |
355 					    WDIOF_EXTERN1 |
356 					    WDIOF_EXTERN2 |
357 					    WDIOF_POWERUNDER |
358 					    WDIOF_POWEROVER);
359 
360 	if (test_bit(_WDOG_ALLOW_RELEASE, &wd_data->status))
361 		status |= WDIOF_MAGICCLOSE;
362 
363 	if (test_and_clear_bit(_WDOG_KEEPALIVE, &wd_data->status))
364 		status |= WDIOF_KEEPALIVEPING;
365 
366 	return status;
367 }
368 
369 /*
370  *	watchdog_set_timeout: set the watchdog timer timeout
371  *	@wdd: the watchdog device to set the timeout for
372  *	@timeout: timeout to set in seconds
373  *
374  *	The caller must hold wd_data->lock.
375  */
376 
377 static int watchdog_set_timeout(struct watchdog_device *wdd,
378 							unsigned int timeout)
379 {
380 	int err = 0;
381 
382 	if (!(wdd->info->options & WDIOF_SETTIMEOUT))
383 		return -EOPNOTSUPP;
384 
385 	if (watchdog_timeout_invalid(wdd, timeout))
386 		return -EINVAL;
387 
388 	if (wdd->ops->set_timeout) {
389 		err = wdd->ops->set_timeout(wdd, timeout);
390 	} else {
391 		wdd->timeout = timeout;
392 		/* Disable pretimeout if it doesn't fit the new timeout */
393 		if (wdd->pretimeout >= wdd->timeout)
394 			wdd->pretimeout = 0;
395 	}
396 
397 	watchdog_update_worker(wdd);
398 
399 	return err;
400 }
401 
402 /*
403  *	watchdog_set_pretimeout: set the watchdog timer pretimeout
404  *	@wdd: the watchdog device to set the timeout for
405  *	@timeout: pretimeout to set in seconds
406  */
407 
408 static int watchdog_set_pretimeout(struct watchdog_device *wdd,
409 				   unsigned int timeout)
410 {
411 	int err = 0;
412 
413 	if (!(wdd->info->options & WDIOF_PRETIMEOUT))
414 		return -EOPNOTSUPP;
415 
416 	if (watchdog_pretimeout_invalid(wdd, timeout))
417 		return -EINVAL;
418 
419 	if (wdd->ops->set_pretimeout)
420 		err = wdd->ops->set_pretimeout(wdd, timeout);
421 	else
422 		wdd->pretimeout = timeout;
423 
424 	return err;
425 }
426 
427 /*
428  *	watchdog_get_timeleft: wrapper to get the time left before a reboot
429  *	@wdd: the watchdog device to get the remaining time from
430  *	@timeleft: the time that's left
431  *
432  *	The caller must hold wd_data->lock.
433  *
434  *	Get the time before a watchdog will reboot (if not pinged).
435  */
436 
437 static int watchdog_get_timeleft(struct watchdog_device *wdd,
438 							unsigned int *timeleft)
439 {
440 	*timeleft = 0;
441 
442 	if (!wdd->ops->get_timeleft)
443 		return -EOPNOTSUPP;
444 
445 	*timeleft = wdd->ops->get_timeleft(wdd);
446 
447 	return 0;
448 }
449 
450 #ifdef CONFIG_WATCHDOG_SYSFS
451 static ssize_t nowayout_show(struct device *dev, struct device_attribute *attr,
452 				char *buf)
453 {
454 	struct watchdog_device *wdd = dev_get_drvdata(dev);
455 
456 	return sprintf(buf, "%d\n", !!test_bit(WDOG_NO_WAY_OUT, &wdd->status));
457 }
458 
459 static ssize_t nowayout_store(struct device *dev, struct device_attribute *attr,
460 				const char *buf, size_t len)
461 {
462 	struct watchdog_device *wdd = dev_get_drvdata(dev);
463 	unsigned int value;
464 	int ret;
465 
466 	ret = kstrtouint(buf, 0, &value);
467 	if (ret)
468 		return ret;
469 	if (value > 1)
470 		return -EINVAL;
471 	/* nowayout cannot be disabled once set */
472 	if (test_bit(WDOG_NO_WAY_OUT, &wdd->status) && !value)
473 		return -EPERM;
474 	watchdog_set_nowayout(wdd, value);
475 	return len;
476 }
477 static DEVICE_ATTR_RW(nowayout);
478 
479 static ssize_t status_show(struct device *dev, struct device_attribute *attr,
480 				char *buf)
481 {
482 	struct watchdog_device *wdd = dev_get_drvdata(dev);
483 	struct watchdog_core_data *wd_data = wdd->wd_data;
484 	unsigned int status;
485 
486 	mutex_lock(&wd_data->lock);
487 	status = watchdog_get_status(wdd);
488 	mutex_unlock(&wd_data->lock);
489 
490 	return sprintf(buf, "0x%x\n", status);
491 }
492 static DEVICE_ATTR_RO(status);
493 
494 static ssize_t bootstatus_show(struct device *dev,
495 				struct device_attribute *attr, char *buf)
496 {
497 	struct watchdog_device *wdd = dev_get_drvdata(dev);
498 
499 	return sprintf(buf, "%u\n", wdd->bootstatus);
500 }
501 static DEVICE_ATTR_RO(bootstatus);
502 
503 static ssize_t timeleft_show(struct device *dev, struct device_attribute *attr,
504 				char *buf)
505 {
506 	struct watchdog_device *wdd = dev_get_drvdata(dev);
507 	struct watchdog_core_data *wd_data = wdd->wd_data;
508 	ssize_t status;
509 	unsigned int val;
510 
511 	mutex_lock(&wd_data->lock);
512 	status = watchdog_get_timeleft(wdd, &val);
513 	mutex_unlock(&wd_data->lock);
514 	if (!status)
515 		status = sprintf(buf, "%u\n", val);
516 
517 	return status;
518 }
519 static DEVICE_ATTR_RO(timeleft);
520 
521 static ssize_t timeout_show(struct device *dev, struct device_attribute *attr,
522 				char *buf)
523 {
524 	struct watchdog_device *wdd = dev_get_drvdata(dev);
525 
526 	return sprintf(buf, "%u\n", wdd->timeout);
527 }
528 static DEVICE_ATTR_RO(timeout);
529 
530 static ssize_t pretimeout_show(struct device *dev,
531 			       struct device_attribute *attr, char *buf)
532 {
533 	struct watchdog_device *wdd = dev_get_drvdata(dev);
534 
535 	return sprintf(buf, "%u\n", wdd->pretimeout);
536 }
537 static DEVICE_ATTR_RO(pretimeout);
538 
539 static ssize_t identity_show(struct device *dev, struct device_attribute *attr,
540 				char *buf)
541 {
542 	struct watchdog_device *wdd = dev_get_drvdata(dev);
543 
544 	return sprintf(buf, "%s\n", wdd->info->identity);
545 }
546 static DEVICE_ATTR_RO(identity);
547 
548 static ssize_t state_show(struct device *dev, struct device_attribute *attr,
549 				char *buf)
550 {
551 	struct watchdog_device *wdd = dev_get_drvdata(dev);
552 
553 	if (watchdog_active(wdd))
554 		return sprintf(buf, "active\n");
555 
556 	return sprintf(buf, "inactive\n");
557 }
558 static DEVICE_ATTR_RO(state);
559 
560 static ssize_t pretimeout_available_governors_show(struct device *dev,
561 				   struct device_attribute *attr, char *buf)
562 {
563 	return watchdog_pretimeout_available_governors_get(buf);
564 }
565 static DEVICE_ATTR_RO(pretimeout_available_governors);
566 
567 static ssize_t pretimeout_governor_show(struct device *dev,
568 					struct device_attribute *attr,
569 					char *buf)
570 {
571 	struct watchdog_device *wdd = dev_get_drvdata(dev);
572 
573 	return watchdog_pretimeout_governor_get(wdd, buf);
574 }
575 
576 static ssize_t pretimeout_governor_store(struct device *dev,
577 					 struct device_attribute *attr,
578 					 const char *buf, size_t count)
579 {
580 	struct watchdog_device *wdd = dev_get_drvdata(dev);
581 	int ret = watchdog_pretimeout_governor_set(wdd, buf);
582 
583 	if (!ret)
584 		ret = count;
585 
586 	return ret;
587 }
588 static DEVICE_ATTR_RW(pretimeout_governor);
589 
590 static umode_t wdt_is_visible(struct kobject *kobj, struct attribute *attr,
591 				int n)
592 {
593 	struct device *dev = kobj_to_dev(kobj);
594 	struct watchdog_device *wdd = dev_get_drvdata(dev);
595 	umode_t mode = attr->mode;
596 
597 	if (attr == &dev_attr_timeleft.attr && !wdd->ops->get_timeleft)
598 		mode = 0;
599 	else if (attr == &dev_attr_pretimeout.attr &&
600 		 !(wdd->info->options & WDIOF_PRETIMEOUT))
601 		mode = 0;
602 	else if ((attr == &dev_attr_pretimeout_governor.attr ||
603 		  attr == &dev_attr_pretimeout_available_governors.attr) &&
604 		 (!(wdd->info->options & WDIOF_PRETIMEOUT) ||
605 		  !IS_ENABLED(CONFIG_WATCHDOG_PRETIMEOUT_GOV)))
606 		mode = 0;
607 
608 	return mode;
609 }
610 static struct attribute *wdt_attrs[] = {
611 	&dev_attr_state.attr,
612 	&dev_attr_identity.attr,
613 	&dev_attr_timeout.attr,
614 	&dev_attr_pretimeout.attr,
615 	&dev_attr_timeleft.attr,
616 	&dev_attr_bootstatus.attr,
617 	&dev_attr_status.attr,
618 	&dev_attr_nowayout.attr,
619 	&dev_attr_pretimeout_governor.attr,
620 	&dev_attr_pretimeout_available_governors.attr,
621 	NULL,
622 };
623 
624 static const struct attribute_group wdt_group = {
625 	.attrs = wdt_attrs,
626 	.is_visible = wdt_is_visible,
627 };
628 __ATTRIBUTE_GROUPS(wdt);
629 #else
630 #define wdt_groups	NULL
631 #endif
632 
633 /*
634  *	watchdog_ioctl_op: call the watchdog drivers ioctl op if defined
635  *	@wdd: the watchdog device to do the ioctl on
636  *	@cmd: watchdog command
637  *	@arg: argument pointer
638  *
639  *	The caller must hold wd_data->lock.
640  */
641 
642 static int watchdog_ioctl_op(struct watchdog_device *wdd, unsigned int cmd,
643 							unsigned long arg)
644 {
645 	if (!wdd->ops->ioctl)
646 		return -ENOIOCTLCMD;
647 
648 	return wdd->ops->ioctl(wdd, cmd, arg);
649 }
650 
651 /*
652  *	watchdog_write: writes to the watchdog.
653  *	@file: file from VFS
654  *	@data: user address of data
655  *	@len: length of data
656  *	@ppos: pointer to the file offset
657  *
658  *	A write to a watchdog device is defined as a keepalive ping.
659  *	Writing the magic 'V' sequence allows the next close to turn
660  *	off the watchdog (if 'nowayout' is not set).
661  */
662 
663 static ssize_t watchdog_write(struct file *file, const char __user *data,
664 						size_t len, loff_t *ppos)
665 {
666 	struct watchdog_core_data *wd_data = file->private_data;
667 	struct watchdog_device *wdd;
668 	int err;
669 	size_t i;
670 	char c;
671 
672 	if (len == 0)
673 		return 0;
674 
675 	/*
676 	 * Note: just in case someone wrote the magic character
677 	 * five months ago...
678 	 */
679 	clear_bit(_WDOG_ALLOW_RELEASE, &wd_data->status);
680 
681 	/* scan to see whether or not we got the magic character */
682 	for (i = 0; i != len; i++) {
683 		if (get_user(c, data + i))
684 			return -EFAULT;
685 		if (c == 'V')
686 			set_bit(_WDOG_ALLOW_RELEASE, &wd_data->status);
687 	}
688 
689 	/* someone wrote to us, so we send the watchdog a keepalive ping */
690 
691 	err = -ENODEV;
692 	mutex_lock(&wd_data->lock);
693 	wdd = wd_data->wdd;
694 	if (wdd)
695 		err = watchdog_ping(wdd);
696 	mutex_unlock(&wd_data->lock);
697 
698 	if (err < 0)
699 		return err;
700 
701 	return len;
702 }
703 
704 /*
705  *	watchdog_ioctl: handle the different ioctl's for the watchdog device.
706  *	@file: file handle to the device
707  *	@cmd: watchdog command
708  *	@arg: argument pointer
709  *
710  *	The watchdog API defines a common set of functions for all watchdogs
711  *	according to their available features.
712  */
713 
714 static long watchdog_ioctl(struct file *file, unsigned int cmd,
715 							unsigned long arg)
716 {
717 	struct watchdog_core_data *wd_data = file->private_data;
718 	void __user *argp = (void __user *)arg;
719 	struct watchdog_device *wdd;
720 	int __user *p = argp;
721 	unsigned int val;
722 	int err;
723 
724 	mutex_lock(&wd_data->lock);
725 
726 	wdd = wd_data->wdd;
727 	if (!wdd) {
728 		err = -ENODEV;
729 		goto out_ioctl;
730 	}
731 
732 	err = watchdog_ioctl_op(wdd, cmd, arg);
733 	if (err != -ENOIOCTLCMD)
734 		goto out_ioctl;
735 
736 	switch (cmd) {
737 	case WDIOC_GETSUPPORT:
738 		err = copy_to_user(argp, wdd->info,
739 			sizeof(struct watchdog_info)) ? -EFAULT : 0;
740 		break;
741 	case WDIOC_GETSTATUS:
742 		val = watchdog_get_status(wdd);
743 		err = put_user(val, p);
744 		break;
745 	case WDIOC_GETBOOTSTATUS:
746 		err = put_user(wdd->bootstatus, p);
747 		break;
748 	case WDIOC_SETOPTIONS:
749 		if (get_user(val, p)) {
750 			err = -EFAULT;
751 			break;
752 		}
753 		if (val & WDIOS_DISABLECARD) {
754 			err = watchdog_stop(wdd);
755 			if (err < 0)
756 				break;
757 		}
758 		if (val & WDIOS_ENABLECARD)
759 			err = watchdog_start(wdd);
760 		break;
761 	case WDIOC_KEEPALIVE:
762 		if (!(wdd->info->options & WDIOF_KEEPALIVEPING)) {
763 			err = -EOPNOTSUPP;
764 			break;
765 		}
766 		err = watchdog_ping(wdd);
767 		break;
768 	case WDIOC_SETTIMEOUT:
769 		if (get_user(val, p)) {
770 			err = -EFAULT;
771 			break;
772 		}
773 		err = watchdog_set_timeout(wdd, val);
774 		if (err < 0)
775 			break;
776 		/* If the watchdog is active then we send a keepalive ping
777 		 * to make sure that the watchdog keep's running (and if
778 		 * possible that it takes the new timeout) */
779 		err = watchdog_ping(wdd);
780 		if (err < 0)
781 			break;
782 		fallthrough;
783 	case WDIOC_GETTIMEOUT:
784 		/* timeout == 0 means that we don't know the timeout */
785 		if (wdd->timeout == 0) {
786 			err = -EOPNOTSUPP;
787 			break;
788 		}
789 		err = put_user(wdd->timeout, p);
790 		break;
791 	case WDIOC_GETTIMELEFT:
792 		err = watchdog_get_timeleft(wdd, &val);
793 		if (err < 0)
794 			break;
795 		err = put_user(val, p);
796 		break;
797 	case WDIOC_SETPRETIMEOUT:
798 		if (get_user(val, p)) {
799 			err = -EFAULT;
800 			break;
801 		}
802 		err = watchdog_set_pretimeout(wdd, val);
803 		break;
804 	case WDIOC_GETPRETIMEOUT:
805 		err = put_user(wdd->pretimeout, p);
806 		break;
807 	default:
808 		err = -ENOTTY;
809 		break;
810 	}
811 
812 out_ioctl:
813 	mutex_unlock(&wd_data->lock);
814 	return err;
815 }
816 
817 /*
818  *	watchdog_open: open the /dev/watchdog* devices.
819  *	@inode: inode of device
820  *	@file: file handle to device
821  *
822  *	When the /dev/watchdog* device gets opened, we start the watchdog.
823  *	Watch out: the /dev/watchdog device is single open, so we make sure
824  *	it can only be opened once.
825  */
826 
827 static int watchdog_open(struct inode *inode, struct file *file)
828 {
829 	struct watchdog_core_data *wd_data;
830 	struct watchdog_device *wdd;
831 	bool hw_running;
832 	int err;
833 
834 	/* Get the corresponding watchdog device */
835 	if (imajor(inode) == MISC_MAJOR)
836 		wd_data = old_wd_data;
837 	else
838 		wd_data = container_of(inode->i_cdev, struct watchdog_core_data,
839 				       cdev);
840 
841 	/* the watchdog is single open! */
842 	if (test_and_set_bit(_WDOG_DEV_OPEN, &wd_data->status))
843 		return -EBUSY;
844 
845 	wdd = wd_data->wdd;
846 
847 	/*
848 	 * If the /dev/watchdog device is open, we don't want the module
849 	 * to be unloaded.
850 	 */
851 	hw_running = watchdog_hw_running(wdd);
852 	if (!hw_running && !try_module_get(wdd->ops->owner)) {
853 		err = -EBUSY;
854 		goto out_clear;
855 	}
856 
857 	err = watchdog_start(wdd);
858 	if (err < 0)
859 		goto out_mod;
860 
861 	file->private_data = wd_data;
862 
863 	if (!hw_running)
864 		get_device(&wd_data->dev);
865 
866 	/*
867 	 * open_timeout only applies for the first open from
868 	 * userspace. Set open_deadline to infinity so that the kernel
869 	 * will take care of an always-running hardware watchdog in
870 	 * case the device gets magic-closed or WDIOS_DISABLECARD is
871 	 * applied.
872 	 */
873 	wd_data->open_deadline = KTIME_MAX;
874 
875 	/* dev/watchdog is a virtual (and thus non-seekable) filesystem */
876 	return stream_open(inode, file);
877 
878 out_mod:
879 	module_put(wd_data->wdd->ops->owner);
880 out_clear:
881 	clear_bit(_WDOG_DEV_OPEN, &wd_data->status);
882 	return err;
883 }
884 
885 static void watchdog_core_data_release(struct device *dev)
886 {
887 	struct watchdog_core_data *wd_data;
888 
889 	wd_data = container_of(dev, struct watchdog_core_data, dev);
890 
891 	kfree(wd_data);
892 }
893 
894 /*
895  *	watchdog_release: release the watchdog device.
896  *	@inode: inode of device
897  *	@file: file handle to device
898  *
899  *	This is the code for when /dev/watchdog gets closed. We will only
900  *	stop the watchdog when we have received the magic char (and nowayout
901  *	was not set), else the watchdog will keep running.
902  */
903 
904 static int watchdog_release(struct inode *inode, struct file *file)
905 {
906 	struct watchdog_core_data *wd_data = file->private_data;
907 	struct watchdog_device *wdd;
908 	int err = -EBUSY;
909 	bool running;
910 
911 	mutex_lock(&wd_data->lock);
912 
913 	wdd = wd_data->wdd;
914 	if (!wdd)
915 		goto done;
916 
917 	/*
918 	 * We only stop the watchdog if we received the magic character
919 	 * or if WDIOF_MAGICCLOSE is not set. If nowayout was set then
920 	 * watchdog_stop will fail.
921 	 */
922 	if (!watchdog_active(wdd))
923 		err = 0;
924 	else if (test_and_clear_bit(_WDOG_ALLOW_RELEASE, &wd_data->status) ||
925 		 !(wdd->info->options & WDIOF_MAGICCLOSE))
926 		err = watchdog_stop(wdd);
927 
928 	/* If the watchdog was not stopped, send a keepalive ping */
929 	if (err < 0) {
930 		pr_crit("watchdog%d: watchdog did not stop!\n", wdd->id);
931 		watchdog_ping(wdd);
932 	}
933 
934 	watchdog_update_worker(wdd);
935 
936 	/* make sure that /dev/watchdog can be re-opened */
937 	clear_bit(_WDOG_DEV_OPEN, &wd_data->status);
938 
939 done:
940 	running = wdd && watchdog_hw_running(wdd);
941 	mutex_unlock(&wd_data->lock);
942 	/*
943 	 * Allow the owner module to be unloaded again unless the watchdog
944 	 * is still running. If the watchdog is still running, it can not
945 	 * be stopped, and its driver must not be unloaded.
946 	 */
947 	if (!running) {
948 		module_put(wd_data->cdev.owner);
949 		put_device(&wd_data->dev);
950 	}
951 	return 0;
952 }
953 
954 static const struct file_operations watchdog_fops = {
955 	.owner		= THIS_MODULE,
956 	.write		= watchdog_write,
957 	.unlocked_ioctl	= watchdog_ioctl,
958 	.compat_ioctl	= compat_ptr_ioctl,
959 	.open		= watchdog_open,
960 	.release	= watchdog_release,
961 };
962 
963 static struct miscdevice watchdog_miscdev = {
964 	.minor		= WATCHDOG_MINOR,
965 	.name		= "watchdog",
966 	.fops		= &watchdog_fops,
967 };
968 
969 static struct class watchdog_class = {
970 	.name =		"watchdog",
971 	.owner =	THIS_MODULE,
972 	.dev_groups =	wdt_groups,
973 };
974 
975 /*
976  *	watchdog_cdev_register: register watchdog character device
977  *	@wdd: watchdog device
978  *
979  *	Register a watchdog character device including handling the legacy
980  *	/dev/watchdog node. /dev/watchdog is actually a miscdevice and
981  *	thus we set it up like that.
982  */
983 
984 static int watchdog_cdev_register(struct watchdog_device *wdd)
985 {
986 	struct watchdog_core_data *wd_data;
987 	int err;
988 
989 	wd_data = kzalloc(sizeof(struct watchdog_core_data), GFP_KERNEL);
990 	if (!wd_data)
991 		return -ENOMEM;
992 	mutex_init(&wd_data->lock);
993 
994 	wd_data->wdd = wdd;
995 	wdd->wd_data = wd_data;
996 
997 	if (IS_ERR_OR_NULL(watchdog_kworker))
998 		return -ENODEV;
999 
1000 	device_initialize(&wd_data->dev);
1001 	wd_data->dev.devt = MKDEV(MAJOR(watchdog_devt), wdd->id);
1002 	wd_data->dev.class = &watchdog_class;
1003 	wd_data->dev.parent = wdd->parent;
1004 	wd_data->dev.groups = wdd->groups;
1005 	wd_data->dev.release = watchdog_core_data_release;
1006 	dev_set_drvdata(&wd_data->dev, wdd);
1007 	dev_set_name(&wd_data->dev, "watchdog%d", wdd->id);
1008 
1009 	kthread_init_work(&wd_data->work, watchdog_ping_work);
1010 	hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
1011 	wd_data->timer.function = watchdog_timer_expired;
1012 
1013 	if (wdd->id == 0) {
1014 		old_wd_data = wd_data;
1015 		watchdog_miscdev.parent = wdd->parent;
1016 		err = misc_register(&watchdog_miscdev);
1017 		if (err != 0) {
1018 			pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n",
1019 				wdd->info->identity, WATCHDOG_MINOR, err);
1020 			if (err == -EBUSY)
1021 				pr_err("%s: a legacy watchdog module is probably present.\n",
1022 					wdd->info->identity);
1023 			old_wd_data = NULL;
1024 			kfree(wd_data);
1025 			return err;
1026 		}
1027 	}
1028 
1029 	/* Fill in the data structures */
1030 	cdev_init(&wd_data->cdev, &watchdog_fops);
1031 
1032 	/* Add the device */
1033 	err = cdev_device_add(&wd_data->cdev, &wd_data->dev);
1034 	if (err) {
1035 		pr_err("watchdog%d unable to add device %d:%d\n",
1036 			wdd->id,  MAJOR(watchdog_devt), wdd->id);
1037 		if (wdd->id == 0) {
1038 			misc_deregister(&watchdog_miscdev);
1039 			old_wd_data = NULL;
1040 			put_device(&wd_data->dev);
1041 		}
1042 		return err;
1043 	}
1044 
1045 	wd_data->cdev.owner = wdd->ops->owner;
1046 
1047 	/* Record time of most recent heartbeat as 'just before now'. */
1048 	wd_data->last_hw_keepalive = ktime_sub(ktime_get(), 1);
1049 	watchdog_set_open_deadline(wd_data);
1050 
1051 	/*
1052 	 * If the watchdog is running, prevent its driver from being unloaded,
1053 	 * and schedule an immediate ping.
1054 	 */
1055 	if (watchdog_hw_running(wdd)) {
1056 		__module_get(wdd->ops->owner);
1057 		get_device(&wd_data->dev);
1058 		if (handle_boot_enabled)
1059 			hrtimer_start(&wd_data->timer, 0,
1060 				      HRTIMER_MODE_REL_HARD);
1061 		else
1062 			pr_info("watchdog%d running and kernel based pre-userspace handler disabled\n",
1063 				wdd->id);
1064 	}
1065 
1066 	return 0;
1067 }
1068 
1069 /*
1070  *	watchdog_cdev_unregister: unregister watchdog character device
1071  *	@watchdog: watchdog device
1072  *
1073  *	Unregister watchdog character device and if needed the legacy
1074  *	/dev/watchdog device.
1075  */
1076 
1077 static void watchdog_cdev_unregister(struct watchdog_device *wdd)
1078 {
1079 	struct watchdog_core_data *wd_data = wdd->wd_data;
1080 
1081 	cdev_device_del(&wd_data->cdev, &wd_data->dev);
1082 	if (wdd->id == 0) {
1083 		misc_deregister(&watchdog_miscdev);
1084 		old_wd_data = NULL;
1085 	}
1086 
1087 	if (watchdog_active(wdd) &&
1088 	    test_bit(WDOG_STOP_ON_UNREGISTER, &wdd->status)) {
1089 		watchdog_stop(wdd);
1090 	}
1091 
1092 	mutex_lock(&wd_data->lock);
1093 	wd_data->wdd = NULL;
1094 	wdd->wd_data = NULL;
1095 	mutex_unlock(&wd_data->lock);
1096 
1097 	hrtimer_cancel(&wd_data->timer);
1098 	kthread_cancel_work_sync(&wd_data->work);
1099 
1100 	put_device(&wd_data->dev);
1101 }
1102 
1103 /*
1104  *	watchdog_dev_register: register a watchdog device
1105  *	@wdd: watchdog device
1106  *
1107  *	Register a watchdog device including handling the legacy
1108  *	/dev/watchdog node. /dev/watchdog is actually a miscdevice and
1109  *	thus we set it up like that.
1110  */
1111 
1112 int watchdog_dev_register(struct watchdog_device *wdd)
1113 {
1114 	int ret;
1115 
1116 	ret = watchdog_cdev_register(wdd);
1117 	if (ret)
1118 		return ret;
1119 
1120 	ret = watchdog_register_pretimeout(wdd);
1121 	if (ret)
1122 		watchdog_cdev_unregister(wdd);
1123 
1124 	return ret;
1125 }
1126 
1127 /*
1128  *	watchdog_dev_unregister: unregister a watchdog device
1129  *	@watchdog: watchdog device
1130  *
1131  *	Unregister watchdog device and if needed the legacy
1132  *	/dev/watchdog device.
1133  */
1134 
1135 void watchdog_dev_unregister(struct watchdog_device *wdd)
1136 {
1137 	watchdog_unregister_pretimeout(wdd);
1138 	watchdog_cdev_unregister(wdd);
1139 }
1140 
1141 /*
1142  *	watchdog_set_last_hw_keepalive: set last HW keepalive time for watchdog
1143  *	@wdd: watchdog device
1144  *	@last_ping_ms: time since last HW heartbeat
1145  *
1146  *	Adjusts the last known HW keepalive time for a watchdog timer.
1147  *	This is needed if the watchdog is already running when the probe
1148  *	function is called, and it can't be pinged immediately. This
1149  *	function must be called immediately after watchdog registration,
1150  *	and min_hw_heartbeat_ms must be set for this to be useful.
1151  */
1152 int watchdog_set_last_hw_keepalive(struct watchdog_device *wdd,
1153 				   unsigned int last_ping_ms)
1154 {
1155 	struct watchdog_core_data *wd_data;
1156 	ktime_t now;
1157 
1158 	if (!wdd)
1159 		return -EINVAL;
1160 
1161 	wd_data = wdd->wd_data;
1162 
1163 	now = ktime_get();
1164 
1165 	wd_data->last_hw_keepalive = ktime_sub(now, ms_to_ktime(last_ping_ms));
1166 
1167 	return __watchdog_ping(wdd);
1168 }
1169 EXPORT_SYMBOL_GPL(watchdog_set_last_hw_keepalive);
1170 
1171 /*
1172  *	watchdog_dev_init: init dev part of watchdog core
1173  *
1174  *	Allocate a range of chardev nodes to use for watchdog devices
1175  */
1176 
1177 int __init watchdog_dev_init(void)
1178 {
1179 	int err;
1180 
1181 	watchdog_kworker = kthread_create_worker(0, "watchdogd");
1182 	if (IS_ERR(watchdog_kworker)) {
1183 		pr_err("Failed to create watchdog kworker\n");
1184 		return PTR_ERR(watchdog_kworker);
1185 	}
1186 	sched_set_fifo(watchdog_kworker->task);
1187 
1188 	err = class_register(&watchdog_class);
1189 	if (err < 0) {
1190 		pr_err("couldn't register class\n");
1191 		goto err_register;
1192 	}
1193 
1194 	err = alloc_chrdev_region(&watchdog_devt, 0, MAX_DOGS, "watchdog");
1195 	if (err < 0) {
1196 		pr_err("watchdog: unable to allocate char dev region\n");
1197 		goto err_alloc;
1198 	}
1199 
1200 	return 0;
1201 
1202 err_alloc:
1203 	class_unregister(&watchdog_class);
1204 err_register:
1205 	kthread_destroy_worker(watchdog_kworker);
1206 	return err;
1207 }
1208 
1209 /*
1210  *	watchdog_dev_exit: exit dev part of watchdog core
1211  *
1212  *	Release the range of chardev nodes used for watchdog devices
1213  */
1214 
1215 void __exit watchdog_dev_exit(void)
1216 {
1217 	unregister_chrdev_region(watchdog_devt, MAX_DOGS);
1218 	class_unregister(&watchdog_class);
1219 	kthread_destroy_worker(watchdog_kworker);
1220 }
1221 
1222 module_param(handle_boot_enabled, bool, 0444);
1223 MODULE_PARM_DESC(handle_boot_enabled,
1224 	"Watchdog core auto-updates boot enabled watchdogs before userspace takes over (default="
1225 	__MODULE_STRING(IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED)) ")");
1226 
1227 module_param(open_timeout, uint, 0644);
1228 MODULE_PARM_DESC(open_timeout,
1229 	"Maximum time (in seconds, 0 means infinity) for userspace to take over a running watchdog (default="
1230 	__MODULE_STRING(CONFIG_WATCHDOG_OPEN_TIMEOUT) ")");
1231