2 * linux/kernel/time/clocksource.c
4 * This file contains the functions which manage clocksource drivers.
6 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
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.
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.
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.
23 * o Allow clocksource drivers to be unregistered
26 #include <linux/clocksource.h>
27 #include <linux/sysdev.h>
28 #include <linux/init.h>
29 #include <linux/module.h>
30 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
31 #include <linux/tick.h>
33 void timecounter_init(struct timecounter *tc,
34 const struct cyclecounter *cc,
38 tc->cycle_last = cc->read(cc);
39 tc->nsec = start_tstamp;
41 EXPORT_SYMBOL(timecounter_init);
44 * timecounter_read_delta - get nanoseconds since last call of this function
45 * @tc: Pointer to time counter
47 * When the underlying cycle counter runs over, this will be handled
48 * correctly as long as it does not run over more than once between
51 * The first call to this function for a new time counter initializes
52 * the time tracking and returns an undefined result.
54 static u64 timecounter_read_delta(struct timecounter *tc)
56 cycle_t cycle_now, cycle_delta;
59 /* read cycle counter: */
60 cycle_now = tc->cc->read(tc->cc);
62 /* calculate the delta since the last timecounter_read_delta(): */
63 cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
65 /* convert to nanoseconds: */
66 ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta);
68 /* update time stamp of timecounter_read_delta() call: */
69 tc->cycle_last = cycle_now;
74 u64 timecounter_read(struct timecounter *tc)
78 /* increment time by nanoseconds since last call */
79 nsec = timecounter_read_delta(tc);
85 EXPORT_SYMBOL(timecounter_read);
87 u64 timecounter_cyc2time(struct timecounter *tc,
90 u64 cycle_delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
94 * Instead of always treating cycle_tstamp as more recent
95 * than tc->cycle_last, detect when it is too far in the
96 * future and treat it as old time stamp instead.
98 if (cycle_delta > tc->cc->mask / 2) {
99 cycle_delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
100 nsec = tc->nsec - cyclecounter_cyc2ns(tc->cc, cycle_delta);
102 nsec = cyclecounter_cyc2ns(tc->cc, cycle_delta) + tc->nsec;
107 EXPORT_SYMBOL(timecounter_cyc2time);
109 /*[Clocksource internal variables]---------
111 * currently selected clocksource.
113 * linked list with the registered clocksources
115 * protects manipulations to curr_clocksource and the clocksource_list
117 * Name of the user-specified clocksource.
119 static struct clocksource *curr_clocksource;
120 static LIST_HEAD(clocksource_list);
121 static DEFINE_MUTEX(clocksource_mutex);
122 static char override_name[32];
124 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
125 static LIST_HEAD(watchdog_list);
126 static struct clocksource *watchdog;
127 static struct timer_list watchdog_timer;
128 static struct work_struct watchdog_work;
129 static DEFINE_SPINLOCK(watchdog_lock);
130 static cycle_t watchdog_last;
131 static int watchdog_running;
133 static void clocksource_watchdog_work(struct work_struct *work);
136 * Interval: 0.5sec Threshold: 0.0625s
138 #define WATCHDOG_INTERVAL (HZ >> 1)
139 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
141 static void clocksource_unstable(struct clocksource *cs, int64_t delta)
143 printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
145 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
146 cs->flags |= CLOCK_SOURCE_UNSTABLE;
147 schedule_work(&watchdog_work);
150 static void clocksource_watchdog(unsigned long data)
152 struct clocksource *cs;
153 cycle_t csnow, wdnow;
154 int64_t wd_nsec, cs_nsec;
157 spin_lock(&watchdog_lock);
158 if (!watchdog_running)
161 wdnow = watchdog->read(watchdog);
162 wd_nsec = clocksource_cyc2ns((wdnow - watchdog_last) & watchdog->mask,
163 watchdog->mult, watchdog->shift);
164 watchdog_last = wdnow;
166 list_for_each_entry(cs, &watchdog_list, wd_list) {
168 /* Clocksource already marked unstable? */
169 if (cs->flags & CLOCK_SOURCE_UNSTABLE)
172 csnow = cs->read(cs);
174 /* Clocksource initialized ? */
175 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
176 cs->flags |= CLOCK_SOURCE_WATCHDOG;
181 /* Check the deviation from the watchdog clocksource. */
182 cs_nsec = clocksource_cyc2ns((csnow - cs->wd_last) &
183 cs->mask, cs->mult, cs->shift);
185 if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
186 clocksource_unstable(cs, cs_nsec - wd_nsec);
190 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
191 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
192 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
193 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
195 * We just marked the clocksource as highres-capable,
196 * notify the rest of the system as well so that we
197 * transition into high-res mode:
204 * Cycle through CPUs to check if the CPUs stay synchronized
207 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
208 if (next_cpu >= nr_cpu_ids)
209 next_cpu = cpumask_first(cpu_online_mask);
210 watchdog_timer.expires += WATCHDOG_INTERVAL;
211 add_timer_on(&watchdog_timer, next_cpu);
213 spin_unlock(&watchdog_lock);
216 static inline void clocksource_start_watchdog(void)
218 if (watchdog_running || !watchdog || list_empty(&watchdog_list))
220 INIT_WORK(&watchdog_work, clocksource_watchdog_work);
221 init_timer(&watchdog_timer);
222 watchdog_timer.function = clocksource_watchdog;
223 watchdog_last = watchdog->read(watchdog);
224 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
225 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
226 watchdog_running = 1;
229 static inline void clocksource_stop_watchdog(void)
231 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
233 del_timer(&watchdog_timer);
234 watchdog_running = 0;
237 static inline void clocksource_reset_watchdog(void)
239 struct clocksource *cs;
241 list_for_each_entry(cs, &watchdog_list, wd_list)
242 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
245 static void clocksource_resume_watchdog(void)
249 spin_lock_irqsave(&watchdog_lock, flags);
250 clocksource_reset_watchdog();
251 spin_unlock_irqrestore(&watchdog_lock, flags);
254 static void clocksource_enqueue_watchdog(struct clocksource *cs)
258 spin_lock_irqsave(&watchdog_lock, flags);
259 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
260 /* cs is a clocksource to be watched. */
261 list_add(&cs->wd_list, &watchdog_list);
262 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
264 /* cs is a watchdog. */
265 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
266 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
267 /* Pick the best watchdog. */
268 if (!watchdog || cs->rating > watchdog->rating) {
270 /* Reset watchdog cycles */
271 clocksource_reset_watchdog();
274 /* Check if the watchdog timer needs to be started. */
275 clocksource_start_watchdog();
276 spin_unlock_irqrestore(&watchdog_lock, flags);
279 static void clocksource_dequeue_watchdog(struct clocksource *cs)
281 struct clocksource *tmp;
284 spin_lock_irqsave(&watchdog_lock, flags);
285 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
286 /* cs is a watched clocksource. */
287 list_del_init(&cs->wd_list);
288 } else if (cs == watchdog) {
289 /* Reset watchdog cycles */
290 clocksource_reset_watchdog();
291 /* Current watchdog is removed. Find an alternative. */
293 list_for_each_entry(tmp, &clocksource_list, list) {
294 if (tmp == cs || tmp->flags & CLOCK_SOURCE_MUST_VERIFY)
296 if (!watchdog || tmp->rating > watchdog->rating)
300 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
301 /* Check if the watchdog timer needs to be stopped. */
302 clocksource_stop_watchdog();
303 spin_unlock_irqrestore(&watchdog_lock, flags);
306 static void clocksource_watchdog_work(struct work_struct *work)
308 struct clocksource *cs, *tmp;
312 spin_lock_irqsave(&watchdog_lock, flags);
313 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
314 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
315 list_del_init(&cs->wd_list);
316 list_add(&cs->wd_list, &unstable);
318 /* Check if the watchdog timer needs to be stopped. */
319 clocksource_stop_watchdog();
320 spin_unlock_irqrestore(&watchdog_lock, flags);
322 /* Needs to be done outside of watchdog lock */
323 list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
324 list_del_init(&cs->wd_list);
325 clocksource_change_rating(cs, 0);
329 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */
331 static void clocksource_enqueue_watchdog(struct clocksource *cs)
333 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
334 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
337 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
338 static inline void clocksource_resume_watchdog(void) { }
340 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
343 * clocksource_resume - resume the clocksource(s)
345 void clocksource_resume(void)
347 struct clocksource *cs;
349 mutex_lock(&clocksource_mutex);
351 list_for_each_entry(cs, &clocksource_list, list)
355 clocksource_resume_watchdog();
357 mutex_unlock(&clocksource_mutex);
361 * clocksource_touch_watchdog - Update watchdog
363 * Update the watchdog after exception contexts such as kgdb so as not
364 * to incorrectly trip the watchdog.
367 void clocksource_touch_watchdog(void)
369 clocksource_resume_watchdog();
372 #ifdef CONFIG_GENERIC_TIME
374 static int finished_booting;
377 * clocksource_select - Select the best clocksource available
379 * Private function. Must hold clocksource_mutex when called.
381 * Select the clocksource with the best rating, or the clocksource,
382 * which is selected by userspace override.
384 static void clocksource_select(void)
386 struct clocksource *best, *cs;
388 if (!finished_booting || list_empty(&clocksource_list))
390 /* First clocksource on the list has the best rating. */
391 best = list_first_entry(&clocksource_list, struct clocksource, list);
392 /* Check for the override clocksource. */
393 list_for_each_entry(cs, &clocksource_list, list) {
394 if (strcmp(cs->name, override_name) != 0)
397 * Check to make sure we don't switch to a non-highres
398 * capable clocksource if the tick code is in oneshot
399 * mode (highres or nohz)
401 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
402 tick_oneshot_mode_active()) {
403 /* Override clocksource cannot be used. */
404 printk(KERN_WARNING "Override clocksource %s is not "
405 "HRT compatible. Cannot switch while in "
406 "HRT/NOHZ mode\n", cs->name);
407 override_name[0] = 0;
409 /* Override clocksource can be used. */
413 if (curr_clocksource != best) {
414 printk(KERN_INFO "Switching to clocksource %s\n", best->name);
415 curr_clocksource = best;
416 timekeeping_notify(curr_clocksource);
421 * clocksource_done_booting - Called near the end of core bootup
423 * Hack to avoid lots of clocksource churn at boot time.
424 * We use fs_initcall because we want this to start before
425 * device_initcall but after subsys_initcall.
427 static int __init clocksource_done_booting(void)
429 finished_booting = 1;
430 clocksource_select();
433 fs_initcall(clocksource_done_booting);
435 #else /* CONFIG_GENERIC_TIME */
437 static inline void clocksource_select(void) { }
442 * Enqueue the clocksource sorted by rating
444 static void clocksource_enqueue(struct clocksource *cs)
446 struct list_head *entry = &clocksource_list;
447 struct clocksource *tmp;
449 list_for_each_entry(tmp, &clocksource_list, list)
450 /* Keep track of the place, where to insert */
451 if (tmp->rating >= cs->rating)
453 list_add(&cs->list, entry);
457 * clocksource_register - Used to install new clocksources
458 * @t: clocksource to be registered
460 * Returns -EBUSY if registration fails, zero otherwise.
462 int clocksource_register(struct clocksource *cs)
464 mutex_lock(&clocksource_mutex);
465 clocksource_enqueue(cs);
466 clocksource_select();
467 clocksource_enqueue_watchdog(cs);
468 mutex_unlock(&clocksource_mutex);
471 EXPORT_SYMBOL(clocksource_register);
474 * clocksource_change_rating - Change the rating of a registered clocksource
476 void clocksource_change_rating(struct clocksource *cs, int rating)
478 mutex_lock(&clocksource_mutex);
481 clocksource_enqueue(cs);
482 clocksource_select();
483 mutex_unlock(&clocksource_mutex);
485 EXPORT_SYMBOL(clocksource_change_rating);
488 * clocksource_unregister - remove a registered clocksource
490 void clocksource_unregister(struct clocksource *cs)
492 mutex_lock(&clocksource_mutex);
493 clocksource_dequeue_watchdog(cs);
495 clocksource_select();
496 mutex_unlock(&clocksource_mutex);
498 EXPORT_SYMBOL(clocksource_unregister);
502 * sysfs_show_current_clocksources - sysfs interface for current clocksource
504 * @buf: char buffer to be filled with clocksource list
506 * Provides sysfs interface for listing current clocksource.
509 sysfs_show_current_clocksources(struct sys_device *dev,
510 struct sysdev_attribute *attr, char *buf)
514 mutex_lock(&clocksource_mutex);
515 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
516 mutex_unlock(&clocksource_mutex);
522 * sysfs_override_clocksource - interface for manually overriding clocksource
524 * @buf: name of override clocksource
525 * @count: length of buffer
527 * Takes input from sysfs interface for manually overriding the default
528 * clocksource selction.
530 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
531 struct sysdev_attribute *attr,
532 const char *buf, size_t count)
536 /* strings from sysfs write are not 0 terminated! */
537 if (count >= sizeof(override_name))
541 if (buf[count-1] == '\n')
544 mutex_lock(&clocksource_mutex);
547 memcpy(override_name, buf, count);
548 override_name[count] = 0;
549 clocksource_select();
551 mutex_unlock(&clocksource_mutex);
557 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
559 * @buf: char buffer to be filled with clocksource list
561 * Provides sysfs interface for listing registered clocksources
564 sysfs_show_available_clocksources(struct sys_device *dev,
565 struct sysdev_attribute *attr,
568 struct clocksource *src;
571 mutex_lock(&clocksource_mutex);
572 list_for_each_entry(src, &clocksource_list, list) {
574 * Don't show non-HRES clocksource if the tick code is
575 * in one shot mode (highres=on or nohz=on)
577 if (!tick_oneshot_mode_active() ||
578 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
579 count += snprintf(buf + count,
580 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
583 mutex_unlock(&clocksource_mutex);
585 count += snprintf(buf + count,
586 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
594 static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
595 sysfs_override_clocksource);
597 static SYSDEV_ATTR(available_clocksource, 0444,
598 sysfs_show_available_clocksources, NULL);
600 static struct sysdev_class clocksource_sysclass = {
601 .name = "clocksource",
604 static struct sys_device device_clocksource = {
606 .cls = &clocksource_sysclass,
609 static int __init init_clocksource_sysfs(void)
611 int error = sysdev_class_register(&clocksource_sysclass);
614 error = sysdev_register(&device_clocksource);
616 error = sysdev_create_file(
618 &attr_current_clocksource);
620 error = sysdev_create_file(
622 &attr_available_clocksource);
626 device_initcall(init_clocksource_sysfs);
627 #endif /* CONFIG_SYSFS */
630 * boot_override_clocksource - boot clock override
631 * @str: override name
633 * Takes a clocksource= boot argument and uses it
634 * as the clocksource override name.
636 static int __init boot_override_clocksource(char* str)
638 mutex_lock(&clocksource_mutex);
640 strlcpy(override_name, str, sizeof(override_name));
641 mutex_unlock(&clocksource_mutex);
645 __setup("clocksource=", boot_override_clocksource);
648 * boot_override_clock - Compatibility layer for deprecated boot option
649 * @str: override name
651 * DEPRECATED! Takes a clock= boot argument and uses it
652 * as the clocksource override name
654 static int __init boot_override_clock(char* str)
656 if (!strcmp(str, "pmtmr")) {
657 printk("Warning: clock=pmtmr is deprecated. "
658 "Use clocksource=acpi_pm.\n");
659 return boot_override_clocksource("acpi_pm");
661 printk("Warning! clock= boot option is deprecated. "
662 "Use clocksource=xyz\n");
663 return boot_override_clocksource(str);
666 __setup("clock=", boot_override_clock);