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
);
134 static void __clocksource_change_rating(struct clocksource
*cs
, int rating
);
137 * Interval: 0.5sec Threshold: 0.0625s
139 #define WATCHDOG_INTERVAL (HZ >> 1)
140 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
142 static void clocksource_unstable(struct clocksource
*cs
, int64_t delta
)
144 printk(KERN_WARNING
"Clocksource %s unstable (delta = %Ld ns)\n",
146 cs
->flags
&= ~(CLOCK_SOURCE_VALID_FOR_HRES
| CLOCK_SOURCE_WATCHDOG
);
147 cs
->flags
|= CLOCK_SOURCE_UNSTABLE
;
148 schedule_work(&watchdog_work
);
151 static void clocksource_watchdog(unsigned long data
)
153 struct clocksource
*cs
;
154 cycle_t csnow
, wdnow
;
155 int64_t wd_nsec
, cs_nsec
;
158 spin_lock(&watchdog_lock
);
159 if (!watchdog_running
)
162 wdnow
= watchdog
->read(watchdog
);
163 wd_nsec
= clocksource_cyc2ns((wdnow
- watchdog_last
) & watchdog
->mask
,
164 watchdog
->mult
, watchdog
->shift
);
165 watchdog_last
= wdnow
;
167 list_for_each_entry(cs
, &watchdog_list
, wd_list
) {
169 /* Clocksource already marked unstable? */
170 if (cs
->flags
& CLOCK_SOURCE_UNSTABLE
)
173 csnow
= cs
->read(cs
);
175 /* Clocksource initialized ? */
176 if (!(cs
->flags
& CLOCK_SOURCE_WATCHDOG
)) {
177 cs
->flags
|= CLOCK_SOURCE_WATCHDOG
;
182 /* Check the deviation from the watchdog clocksource. */
183 cs_nsec
= clocksource_cyc2ns((csnow
- cs
->wd_last
) &
184 cs
->mask
, cs
->mult
, cs
->shift
);
186 if (abs(cs_nsec
- wd_nsec
) > WATCHDOG_THRESHOLD
) {
187 clocksource_unstable(cs
, cs_nsec
- wd_nsec
);
191 if (!(cs
->flags
& CLOCK_SOURCE_VALID_FOR_HRES
) &&
192 (cs
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
) &&
193 (watchdog
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
)) {
194 cs
->flags
|= CLOCK_SOURCE_VALID_FOR_HRES
;
196 * We just marked the clocksource as highres-capable,
197 * notify the rest of the system as well so that we
198 * transition into high-res mode:
205 * Cycle through CPUs to check if the CPUs stay synchronized
208 next_cpu
= cpumask_next(raw_smp_processor_id(), cpu_online_mask
);
209 if (next_cpu
>= nr_cpu_ids
)
210 next_cpu
= cpumask_first(cpu_online_mask
);
211 watchdog_timer
.expires
+= WATCHDOG_INTERVAL
;
212 add_timer_on(&watchdog_timer
, next_cpu
);
214 spin_unlock(&watchdog_lock
);
217 static inline void clocksource_start_watchdog(void)
219 if (watchdog_running
|| !watchdog
|| list_empty(&watchdog_list
))
221 INIT_WORK(&watchdog_work
, clocksource_watchdog_work
);
222 init_timer(&watchdog_timer
);
223 watchdog_timer
.function
= clocksource_watchdog
;
224 watchdog_last
= watchdog
->read(watchdog
);
225 watchdog_timer
.expires
= jiffies
+ WATCHDOG_INTERVAL
;
226 add_timer_on(&watchdog_timer
, cpumask_first(cpu_online_mask
));
227 watchdog_running
= 1;
230 static inline void clocksource_stop_watchdog(void)
232 if (!watchdog_running
|| (watchdog
&& !list_empty(&watchdog_list
)))
234 del_timer(&watchdog_timer
);
235 watchdog_running
= 0;
238 static inline void clocksource_reset_watchdog(void)
240 struct clocksource
*cs
;
242 list_for_each_entry(cs
, &watchdog_list
, wd_list
)
243 cs
->flags
&= ~CLOCK_SOURCE_WATCHDOG
;
246 static void clocksource_resume_watchdog(void)
250 spin_lock_irqsave(&watchdog_lock
, flags
);
251 clocksource_reset_watchdog();
252 spin_unlock_irqrestore(&watchdog_lock
, flags
);
255 static void clocksource_enqueue_watchdog(struct clocksource
*cs
)
259 spin_lock_irqsave(&watchdog_lock
, flags
);
260 if (cs
->flags
& CLOCK_SOURCE_MUST_VERIFY
) {
261 /* cs is a clocksource to be watched. */
262 list_add(&cs
->wd_list
, &watchdog_list
);
263 cs
->flags
&= ~CLOCK_SOURCE_WATCHDOG
;
265 /* cs is a watchdog. */
266 if (cs
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
)
267 cs
->flags
|= CLOCK_SOURCE_VALID_FOR_HRES
;
268 /* Pick the best watchdog. */
269 if (!watchdog
|| cs
->rating
> watchdog
->rating
) {
271 /* Reset watchdog cycles */
272 clocksource_reset_watchdog();
275 /* Check if the watchdog timer needs to be started. */
276 clocksource_start_watchdog();
277 spin_unlock_irqrestore(&watchdog_lock
, flags
);
280 static void clocksource_dequeue_watchdog(struct clocksource
*cs
)
282 struct clocksource
*tmp
;
285 spin_lock_irqsave(&watchdog_lock
, flags
);
286 if (cs
->flags
& CLOCK_SOURCE_MUST_VERIFY
) {
287 /* cs is a watched clocksource. */
288 list_del_init(&cs
->wd_list
);
289 } else if (cs
== watchdog
) {
290 /* Reset watchdog cycles */
291 clocksource_reset_watchdog();
292 /* Current watchdog is removed. Find an alternative. */
294 list_for_each_entry(tmp
, &clocksource_list
, list
) {
295 if (tmp
== cs
|| tmp
->flags
& CLOCK_SOURCE_MUST_VERIFY
)
297 if (!watchdog
|| tmp
->rating
> watchdog
->rating
)
301 cs
->flags
&= ~CLOCK_SOURCE_WATCHDOG
;
302 /* Check if the watchdog timer needs to be stopped. */
303 clocksource_stop_watchdog();
304 spin_unlock_irqrestore(&watchdog_lock
, flags
);
307 static void clocksource_watchdog_work(struct work_struct
*work
)
309 struct clocksource
*cs
, *tmp
;
313 mutex_lock(&clocksource_mutex
);
314 spin_lock_irqsave(&watchdog_lock
, flags
);
315 list_for_each_entry_safe(cs
, tmp
, &watchdog_list
, wd_list
)
316 if (cs
->flags
& CLOCK_SOURCE_UNSTABLE
) {
317 list_del_init(&cs
->wd_list
);
318 list_add(&cs
->wd_list
, &unstable
);
320 /* Check if the watchdog timer needs to be stopped. */
321 clocksource_stop_watchdog();
322 spin_unlock_irqrestore(&watchdog_lock
, flags
);
324 /* Needs to be done outside of watchdog lock */
325 list_for_each_entry_safe(cs
, tmp
, &unstable
, wd_list
) {
326 list_del_init(&cs
->wd_list
);
327 __clocksource_change_rating(cs
, 0);
329 mutex_unlock(&clocksource_mutex
);
332 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */
334 static void clocksource_enqueue_watchdog(struct clocksource
*cs
)
336 if (cs
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
)
337 cs
->flags
|= CLOCK_SOURCE_VALID_FOR_HRES
;
340 static inline void clocksource_dequeue_watchdog(struct clocksource
*cs
) { }
341 static inline void clocksource_resume_watchdog(void) { }
343 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
346 * clocksource_resume - resume the clocksource(s)
348 void clocksource_resume(void)
350 struct clocksource
*cs
;
352 mutex_lock(&clocksource_mutex
);
354 list_for_each_entry(cs
, &clocksource_list
, list
)
358 clocksource_resume_watchdog();
360 mutex_unlock(&clocksource_mutex
);
364 * clocksource_touch_watchdog - Update watchdog
366 * Update the watchdog after exception contexts such as kgdb so as not
367 * to incorrectly trip the watchdog.
370 void clocksource_touch_watchdog(void)
372 clocksource_resume_watchdog();
375 #ifdef CONFIG_GENERIC_TIME
377 static int finished_booting
;
380 * clocksource_select - Select the best clocksource available
382 * Private function. Must hold clocksource_mutex when called.
384 * Select the clocksource with the best rating, or the clocksource,
385 * which is selected by userspace override.
387 static void clocksource_select(void)
389 struct clocksource
*best
, *cs
;
391 if (!finished_booting
|| list_empty(&clocksource_list
))
393 /* First clocksource on the list has the best rating. */
394 best
= list_first_entry(&clocksource_list
, struct clocksource
, list
);
395 /* Check for the override clocksource. */
396 list_for_each_entry(cs
, &clocksource_list
, list
) {
397 if (strcmp(cs
->name
, override_name
) != 0)
400 * Check to make sure we don't switch to a non-highres
401 * capable clocksource if the tick code is in oneshot
402 * mode (highres or nohz)
404 if (!(cs
->flags
& CLOCK_SOURCE_VALID_FOR_HRES
) &&
405 tick_oneshot_mode_active()) {
406 /* Override clocksource cannot be used. */
407 printk(KERN_WARNING
"Override clocksource %s is not "
408 "HRT compatible. Cannot switch while in "
409 "HRT/NOHZ mode\n", cs
->name
);
410 override_name
[0] = 0;
412 /* Override clocksource can be used. */
416 if (curr_clocksource
!= best
) {
417 printk(KERN_INFO
"Switching to clocksource %s\n", best
->name
);
418 curr_clocksource
= best
;
419 timekeeping_notify(curr_clocksource
);
424 * clocksource_done_booting - Called near the end of core bootup
426 * Hack to avoid lots of clocksource churn at boot time.
427 * We use fs_initcall because we want this to start before
428 * device_initcall but after subsys_initcall.
430 static int __init
clocksource_done_booting(void)
432 finished_booting
= 1;
433 clocksource_select();
436 fs_initcall(clocksource_done_booting
);
438 #else /* CONFIG_GENERIC_TIME */
440 static inline void clocksource_select(void) { }
445 * Enqueue the clocksource sorted by rating
447 static void clocksource_enqueue(struct clocksource
*cs
)
449 struct list_head
*entry
= &clocksource_list
;
450 struct clocksource
*tmp
;
452 list_for_each_entry(tmp
, &clocksource_list
, list
)
453 /* Keep track of the place, where to insert */
454 if (tmp
->rating
>= cs
->rating
)
456 list_add(&cs
->list
, entry
);
460 * clocksource_register - Used to install new clocksources
461 * @t: clocksource to be registered
463 * Returns -EBUSY if registration fails, zero otherwise.
465 int clocksource_register(struct clocksource
*cs
)
467 mutex_lock(&clocksource_mutex
);
468 clocksource_enqueue(cs
);
469 clocksource_select();
470 clocksource_enqueue_watchdog(cs
);
471 mutex_unlock(&clocksource_mutex
);
474 EXPORT_SYMBOL(clocksource_register
);
476 static void __clocksource_change_rating(struct clocksource
*cs
, int rating
)
480 clocksource_enqueue(cs
);
481 clocksource_select();
485 * clocksource_change_rating - Change the rating of a registered clocksource
487 void clocksource_change_rating(struct clocksource
*cs
, int rating
)
489 mutex_lock(&clocksource_mutex
);
490 __clocksource_change_rating(cs
, rating
);
491 mutex_unlock(&clocksource_mutex
);
493 EXPORT_SYMBOL(clocksource_change_rating
);
496 * clocksource_unregister - remove a registered clocksource
498 void clocksource_unregister(struct clocksource
*cs
)
500 mutex_lock(&clocksource_mutex
);
501 clocksource_dequeue_watchdog(cs
);
503 clocksource_select();
504 mutex_unlock(&clocksource_mutex
);
506 EXPORT_SYMBOL(clocksource_unregister
);
510 * sysfs_show_current_clocksources - sysfs interface for current clocksource
512 * @buf: char buffer to be filled with clocksource list
514 * Provides sysfs interface for listing current clocksource.
517 sysfs_show_current_clocksources(struct sys_device
*dev
,
518 struct sysdev_attribute
*attr
, char *buf
)
522 mutex_lock(&clocksource_mutex
);
523 count
= snprintf(buf
, PAGE_SIZE
, "%s\n", curr_clocksource
->name
);
524 mutex_unlock(&clocksource_mutex
);
530 * sysfs_override_clocksource - interface for manually overriding clocksource
532 * @buf: name of override clocksource
533 * @count: length of buffer
535 * Takes input from sysfs interface for manually overriding the default
536 * clocksource selction.
538 static ssize_t
sysfs_override_clocksource(struct sys_device
*dev
,
539 struct sysdev_attribute
*attr
,
540 const char *buf
, size_t count
)
544 /* strings from sysfs write are not 0 terminated! */
545 if (count
>= sizeof(override_name
))
549 if (buf
[count
-1] == '\n')
552 mutex_lock(&clocksource_mutex
);
555 memcpy(override_name
, buf
, count
);
556 override_name
[count
] = 0;
557 clocksource_select();
559 mutex_unlock(&clocksource_mutex
);
565 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
567 * @buf: char buffer to be filled with clocksource list
569 * Provides sysfs interface for listing registered clocksources
572 sysfs_show_available_clocksources(struct sys_device
*dev
,
573 struct sysdev_attribute
*attr
,
576 struct clocksource
*src
;
579 mutex_lock(&clocksource_mutex
);
580 list_for_each_entry(src
, &clocksource_list
, list
) {
582 * Don't show non-HRES clocksource if the tick code is
583 * in one shot mode (highres=on or nohz=on)
585 if (!tick_oneshot_mode_active() ||
586 (src
->flags
& CLOCK_SOURCE_VALID_FOR_HRES
))
587 count
+= snprintf(buf
+ count
,
588 max((ssize_t
)PAGE_SIZE
- count
, (ssize_t
)0),
591 mutex_unlock(&clocksource_mutex
);
593 count
+= snprintf(buf
+ count
,
594 max((ssize_t
)PAGE_SIZE
- count
, (ssize_t
)0), "\n");
602 static SYSDEV_ATTR(current_clocksource
, 0644, sysfs_show_current_clocksources
,
603 sysfs_override_clocksource
);
605 static SYSDEV_ATTR(available_clocksource
, 0444,
606 sysfs_show_available_clocksources
, NULL
);
608 static struct sysdev_class clocksource_sysclass
= {
609 .name
= "clocksource",
612 static struct sys_device device_clocksource
= {
614 .cls
= &clocksource_sysclass
,
617 static int __init
init_clocksource_sysfs(void)
619 int error
= sysdev_class_register(&clocksource_sysclass
);
622 error
= sysdev_register(&device_clocksource
);
624 error
= sysdev_create_file(
626 &attr_current_clocksource
);
628 error
= sysdev_create_file(
630 &attr_available_clocksource
);
634 device_initcall(init_clocksource_sysfs
);
635 #endif /* CONFIG_SYSFS */
638 * boot_override_clocksource - boot clock override
639 * @str: override name
641 * Takes a clocksource= boot argument and uses it
642 * as the clocksource override name.
644 static int __init
boot_override_clocksource(char* str
)
646 mutex_lock(&clocksource_mutex
);
648 strlcpy(override_name
, str
, sizeof(override_name
));
649 mutex_unlock(&clocksource_mutex
);
653 __setup("clocksource=", boot_override_clocksource
);
656 * boot_override_clock - Compatibility layer for deprecated boot option
657 * @str: override name
659 * DEPRECATED! Takes a clock= boot argument and uses it
660 * as the clocksource override name
662 static int __init
boot_override_clock(char* str
)
664 if (!strcmp(str
, "pmtmr")) {
665 printk("Warning: clock=pmtmr is deprecated. "
666 "Use clocksource=acpi_pm.\n");
667 return boot_override_clocksource("acpi_pm");
669 printk("Warning! clock= boot option is deprecated. "
670 "Use clocksource=xyz\n");
671 return boot_override_clocksource(str
);
674 __setup("clock=", boot_override_clock
);