xref: /openbmc/linux/kernel/time/clocksource.c (revision 64c70b1c) 
1 /*
2  * linux/kernel/time/clocksource.c
3  *
4  * This file contains the functions which manage clocksource drivers.
5  *
6  * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
7  *
8  * This program is free software; you can redistribute it and/or modify
9  * it under the terms of the GNU General Public License as published by
10  * the Free Software Foundation; either version 2 of the License, or
11  * (at your option) any later version.
12  *
13  * This program is distributed in the hope that it will be useful,
14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
16  * GNU General Public License for more details.
17  *
18  * You should have received a copy of the GNU General Public License
19  * along with this program; if not, write to the Free Software
20  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
21  *
22  * TODO WishList:
23  *   o Allow clocksource drivers to be unregistered
24  *   o get rid of clocksource_jiffies extern
25  */
26 
27 #include <linux/clocksource.h>
28 #include <linux/sysdev.h>
29 #include <linux/init.h>
30 #include <linux/module.h>
31 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
32 #include <linux/tick.h>
33 
34 /* XXX - Would like a better way for initializing curr_clocksource */
35 extern struct clocksource clocksource_jiffies;
36 
37 /*[Clocksource internal variables]---------
38  * curr_clocksource:
39  *	currently selected clocksource. Initialized to clocksource_jiffies.
40  * next_clocksource:
41  *	pending next selected clocksource.
42  * clocksource_list:
43  *	linked list with the registered clocksources
44  * clocksource_lock:
45  *	protects manipulations to curr_clocksource and next_clocksource
46  *	and the clocksource_list
47  * override_name:
48  *	Name of the user-specified clocksource.
49  */
50 static struct clocksource *curr_clocksource = &clocksource_jiffies;
51 static struct clocksource *next_clocksource;
52 static struct clocksource *clocksource_override;
53 static LIST_HEAD(clocksource_list);
54 static DEFINE_SPINLOCK(clocksource_lock);
55 static char override_name[32];
56 static int finished_booting;
57 
58 /* clocksource_done_booting - Called near the end of core bootup
59  *
60  * Hack to avoid lots of clocksource churn at boot time.
61  * We use fs_initcall because we want this to start before
62  * device_initcall but after subsys_initcall.
63  */
64 static int __init clocksource_done_booting(void)
65 {
66 	finished_booting = 1;
67 	return 0;
68 }
69 fs_initcall(clocksource_done_booting);
70 
71 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
72 static LIST_HEAD(watchdog_list);
73 static struct clocksource *watchdog;
74 static struct timer_list watchdog_timer;
75 static DEFINE_SPINLOCK(watchdog_lock);
76 static cycle_t watchdog_last;
77 static unsigned long watchdog_resumed;
78 
79 /*
80  * Interval: 0.5sec Threshold: 0.0625s
81  */
82 #define WATCHDOG_INTERVAL (HZ >> 1)
83 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
84 
85 static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
86 {
87 	if (delta > -WATCHDOG_THRESHOLD && delta < WATCHDOG_THRESHOLD)
88 		return;
89 
90 	printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
91 	       cs->name, delta);
92 	cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
93 	clocksource_change_rating(cs, 0);
94 	cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
95 	list_del(&cs->wd_list);
96 }
97 
98 static void clocksource_watchdog(unsigned long data)
99 {
100 	struct clocksource *cs, *tmp;
101 	cycle_t csnow, wdnow;
102 	int64_t wd_nsec, cs_nsec;
103 	int resumed;
104 
105 	spin_lock(&watchdog_lock);
106 
107 	resumed = test_and_clear_bit(0, &watchdog_resumed);
108 
109 	wdnow = watchdog->read();
110 	wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
111 	watchdog_last = wdnow;
112 
113 	list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
114 		csnow = cs->read();
115 
116 		if (unlikely(resumed)) {
117 			cs->wd_last = csnow;
118 			continue;
119 		}
120 
121 		/* Initialized ? */
122 		if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
123 			if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
124 			    (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
125 				cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
126 				/*
127 				 * We just marked the clocksource as
128 				 * highres-capable, notify the rest of the
129 				 * system as well so that we transition
130 				 * into high-res mode:
131 				 */
132 				tick_clock_notify();
133 			}
134 			cs->flags |= CLOCK_SOURCE_WATCHDOG;
135 			cs->wd_last = csnow;
136 		} else {
137 			cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
138 			cs->wd_last = csnow;
139 			/* Check the delta. Might remove from the list ! */
140 			clocksource_ratewd(cs, cs_nsec - wd_nsec);
141 		}
142 	}
143 
144 	if (!list_empty(&watchdog_list)) {
145 		__mod_timer(&watchdog_timer,
146 			    watchdog_timer.expires + WATCHDOG_INTERVAL);
147 	}
148 	spin_unlock(&watchdog_lock);
149 }
150 static void clocksource_resume_watchdog(void)
151 {
152 	set_bit(0, &watchdog_resumed);
153 }
154 
155 static void clocksource_check_watchdog(struct clocksource *cs)
156 {
157 	struct clocksource *cse;
158 	unsigned long flags;
159 
160 	spin_lock_irqsave(&watchdog_lock, flags);
161 	if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
162 		int started = !list_empty(&watchdog_list);
163 
164 		list_add(&cs->wd_list, &watchdog_list);
165 		if (!started && watchdog) {
166 			watchdog_last = watchdog->read();
167 			watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
168 			add_timer(&watchdog_timer);
169 		}
170 	} else {
171 		if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
172 			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
173 
174 		if (!watchdog || cs->rating > watchdog->rating) {
175 			if (watchdog)
176 				del_timer(&watchdog_timer);
177 			watchdog = cs;
178 			init_timer(&watchdog_timer);
179 			watchdog_timer.function = clocksource_watchdog;
180 
181 			/* Reset watchdog cycles */
182 			list_for_each_entry(cse, &watchdog_list, wd_list)
183 				cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
184 			/* Start if list is not empty */
185 			if (!list_empty(&watchdog_list)) {
186 				watchdog_last = watchdog->read();
187 				watchdog_timer.expires =
188 					jiffies + WATCHDOG_INTERVAL;
189 				add_timer(&watchdog_timer);
190 			}
191 		}
192 	}
193 	spin_unlock_irqrestore(&watchdog_lock, flags);
194 }
195 #else
196 static void clocksource_check_watchdog(struct clocksource *cs)
197 {
198 	if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
199 		cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
200 }
201 
202 static inline void clocksource_resume_watchdog(void) { }
203 #endif
204 
205 /**
206  * clocksource_resume - resume the clocksource(s)
207  */
208 void clocksource_resume(void)
209 {
210 	struct list_head *tmp;
211 	unsigned long flags;
212 
213 	spin_lock_irqsave(&clocksource_lock, flags);
214 
215 	list_for_each(tmp, &clocksource_list) {
216 		struct clocksource *cs;
217 
218 		cs = list_entry(tmp, struct clocksource, list);
219 		if (cs->resume)
220 			cs->resume();
221 	}
222 
223 	clocksource_resume_watchdog();
224 
225 	spin_unlock_irqrestore(&clocksource_lock, flags);
226 }
227 
228 /**
229  * clocksource_get_next - Returns the selected clocksource
230  *
231  */
232 struct clocksource *clocksource_get_next(void)
233 {
234 	unsigned long flags;
235 
236 	spin_lock_irqsave(&clocksource_lock, flags);
237 	if (next_clocksource && finished_booting) {
238 		curr_clocksource = next_clocksource;
239 		next_clocksource = NULL;
240 	}
241 	spin_unlock_irqrestore(&clocksource_lock, flags);
242 
243 	return curr_clocksource;
244 }
245 
246 /**
247  * select_clocksource - Selects the best registered clocksource.
248  *
249  * Private function. Must hold clocksource_lock when called.
250  *
251  * Select the clocksource with the best rating, or the clocksource,
252  * which is selected by userspace override.
253  */
254 static struct clocksource *select_clocksource(void)
255 {
256 	struct clocksource *next;
257 
258 	if (list_empty(&clocksource_list))
259 		return NULL;
260 
261 	if (clocksource_override)
262 		next = clocksource_override;
263 	else
264 		next = list_entry(clocksource_list.next, struct clocksource,
265 				  list);
266 
267 	if (next == curr_clocksource)
268 		return NULL;
269 
270 	return next;
271 }
272 
273 /*
274  * Enqueue the clocksource sorted by rating
275  */
276 static int clocksource_enqueue(struct clocksource *c)
277 {
278 	struct list_head *tmp, *entry = &clocksource_list;
279 
280 	list_for_each(tmp, &clocksource_list) {
281 		struct clocksource *cs;
282 
283 		cs = list_entry(tmp, struct clocksource, list);
284 		if (cs == c)
285 			return -EBUSY;
286 		/* Keep track of the place, where to insert */
287 		if (cs->rating >= c->rating)
288 			entry = tmp;
289 	}
290 	list_add(&c->list, entry);
291 
292 	if (strlen(c->name) == strlen(override_name) &&
293 	    !strcmp(c->name, override_name))
294 		clocksource_override = c;
295 
296 	return 0;
297 }
298 
299 /**
300  * clocksource_register - Used to install new clocksources
301  * @t:		clocksource to be registered
302  *
303  * Returns -EBUSY if registration fails, zero otherwise.
304  */
305 int clocksource_register(struct clocksource *c)
306 {
307 	unsigned long flags;
308 	int ret;
309 
310 	spin_lock_irqsave(&clocksource_lock, flags);
311 	ret = clocksource_enqueue(c);
312 	if (!ret)
313 		next_clocksource = select_clocksource();
314 	spin_unlock_irqrestore(&clocksource_lock, flags);
315 	if (!ret)
316 		clocksource_check_watchdog(c);
317 	return ret;
318 }
319 EXPORT_SYMBOL(clocksource_register);
320 
321 /**
322  * clocksource_change_rating - Change the rating of a registered clocksource
323  *
324  */
325 void clocksource_change_rating(struct clocksource *cs, int rating)
326 {
327 	unsigned long flags;
328 
329 	spin_lock_irqsave(&clocksource_lock, flags);
330 	list_del(&cs->list);
331 	cs->rating = rating;
332 	clocksource_enqueue(cs);
333 	next_clocksource = select_clocksource();
334 	spin_unlock_irqrestore(&clocksource_lock, flags);
335 }
336 
337 #ifdef CONFIG_SYSFS
338 /**
339  * sysfs_show_current_clocksources - sysfs interface for current clocksource
340  * @dev:	unused
341  * @buf:	char buffer to be filled with clocksource list
342  *
343  * Provides sysfs interface for listing current clocksource.
344  */
345 static ssize_t
346 sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
347 {
348 	char *curr = buf;
349 
350 	spin_lock_irq(&clocksource_lock);
351 	curr += sprintf(curr, "%s ", curr_clocksource->name);
352 	spin_unlock_irq(&clocksource_lock);
353 
354 	curr += sprintf(curr, "\n");
355 
356 	return curr - buf;
357 }
358 
359 /**
360  * sysfs_override_clocksource - interface for manually overriding clocksource
361  * @dev:	unused
362  * @buf:	name of override clocksource
363  * @count:	length of buffer
364  *
365  * Takes input from sysfs interface for manually overriding the default
366  * clocksource selction.
367  */
368 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
369 					  const char *buf, size_t count)
370 {
371 	struct clocksource *ovr = NULL;
372 	struct list_head *tmp;
373 	size_t ret = count;
374 	int len;
375 
376 	/* strings from sysfs write are not 0 terminated! */
377 	if (count >= sizeof(override_name))
378 		return -EINVAL;
379 
380 	/* strip of \n: */
381 	if (buf[count-1] == '\n')
382 		count--;
383 
384 	spin_lock_irq(&clocksource_lock);
385 
386 	if (count > 0)
387 		memcpy(override_name, buf, count);
388 	override_name[count] = 0;
389 
390 	len = strlen(override_name);
391 	if (len) {
392 		ovr = clocksource_override;
393 		/* try to select it: */
394 		list_for_each(tmp, &clocksource_list) {
395 			struct clocksource *cs;
396 
397 			cs = list_entry(tmp, struct clocksource, list);
398 			if (strlen(cs->name) == len &&
399 			    !strcmp(cs->name, override_name))
400 				ovr = cs;
401 		}
402 	}
403 
404 	/* Reselect, when the override name has changed */
405 	if (ovr != clocksource_override) {
406 		clocksource_override = ovr;
407 		next_clocksource = select_clocksource();
408 	}
409 
410 	spin_unlock_irq(&clocksource_lock);
411 
412 	return ret;
413 }
414 
415 /**
416  * sysfs_show_available_clocksources - sysfs interface for listing clocksource
417  * @dev:	unused
418  * @buf:	char buffer to be filled with clocksource list
419  *
420  * Provides sysfs interface for listing registered clocksources
421  */
422 static ssize_t
423 sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
424 {
425 	struct list_head *tmp;
426 	char *curr = buf;
427 
428 	spin_lock_irq(&clocksource_lock);
429 	list_for_each(tmp, &clocksource_list) {
430 		struct clocksource *src;
431 
432 		src = list_entry(tmp, struct clocksource, list);
433 		curr += sprintf(curr, "%s ", src->name);
434 	}
435 	spin_unlock_irq(&clocksource_lock);
436 
437 	curr += sprintf(curr, "\n");
438 
439 	return curr - buf;
440 }
441 
442 /*
443  * Sysfs setup bits:
444  */
445 static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
446 		   sysfs_override_clocksource);
447 
448 static SYSDEV_ATTR(available_clocksource, 0600,
449 		   sysfs_show_available_clocksources, NULL);
450 
451 static struct sysdev_class clocksource_sysclass = {
452 	set_kset_name("clocksource"),
453 };
454 
455 static struct sys_device device_clocksource = {
456 	.id	= 0,
457 	.cls	= &clocksource_sysclass,
458 };
459 
460 static int __init init_clocksource_sysfs(void)
461 {
462 	int error = sysdev_class_register(&clocksource_sysclass);
463 
464 	if (!error)
465 		error = sysdev_register(&device_clocksource);
466 	if (!error)
467 		error = sysdev_create_file(
468 				&device_clocksource,
469 				&attr_current_clocksource);
470 	if (!error)
471 		error = sysdev_create_file(
472 				&device_clocksource,
473 				&attr_available_clocksource);
474 	return error;
475 }
476 
477 device_initcall(init_clocksource_sysfs);
478 #endif /* CONFIG_SYSFS */
479 
480 /**
481  * boot_override_clocksource - boot clock override
482  * @str:	override name
483  *
484  * Takes a clocksource= boot argument and uses it
485  * as the clocksource override name.
486  */
487 static int __init boot_override_clocksource(char* str)
488 {
489 	unsigned long flags;
490 	spin_lock_irqsave(&clocksource_lock, flags);
491 	if (str)
492 		strlcpy(override_name, str, sizeof(override_name));
493 	spin_unlock_irqrestore(&clocksource_lock, flags);
494 	return 1;
495 }
496 
497 __setup("clocksource=", boot_override_clocksource);
498 
499 /**
500  * boot_override_clock - Compatibility layer for deprecated boot option
501  * @str:	override name
502  *
503  * DEPRECATED! Takes a clock= boot argument and uses it
504  * as the clocksource override name
505  */
506 static int __init boot_override_clock(char* str)
507 {
508 	if (!strcmp(str, "pmtmr")) {
509 		printk("Warning: clock=pmtmr is deprecated. "
510 			"Use clocksource=acpi_pm.\n");
511 		return boot_override_clocksource("acpi_pm");
512 	}
513 	printk("Warning! clock= boot option is deprecated. "
514 		"Use clocksource=xyz\n");
515 	return boot_override_clocksource(str);
516 }
517 
518 __setup("clock=", boot_override_clock);
519