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>
32 #include <linux/kthread.h>
34 void timecounter_init(struct timecounter
*tc
,
35 const struct cyclecounter
*cc
,
39 tc
->cycle_last
= cc
->read(cc
);
40 tc
->nsec
= start_tstamp
;
42 EXPORT_SYMBOL(timecounter_init
);
45 * timecounter_read_delta - get nanoseconds since last call of this function
46 * @tc: Pointer to time counter
48 * When the underlying cycle counter runs over, this will be handled
49 * correctly as long as it does not run over more than once between
52 * The first call to this function for a new time counter initializes
53 * the time tracking and returns an undefined result.
55 static u64
timecounter_read_delta(struct timecounter
*tc
)
57 cycle_t cycle_now
, cycle_delta
;
60 /* read cycle counter: */
61 cycle_now
= tc
->cc
->read(tc
->cc
);
63 /* calculate the delta since the last timecounter_read_delta(): */
64 cycle_delta
= (cycle_now
- tc
->cycle_last
) & tc
->cc
->mask
;
66 /* convert to nanoseconds: */
67 ns_offset
= cyclecounter_cyc2ns(tc
->cc
, cycle_delta
);
69 /* update time stamp of timecounter_read_delta() call: */
70 tc
->cycle_last
= cycle_now
;
75 u64
timecounter_read(struct timecounter
*tc
)
79 /* increment time by nanoseconds since last call */
80 nsec
= timecounter_read_delta(tc
);
86 EXPORT_SYMBOL(timecounter_read
);
88 u64
timecounter_cyc2time(struct timecounter
*tc
,
91 u64 cycle_delta
= (cycle_tstamp
- tc
->cycle_last
) & tc
->cc
->mask
;
95 * Instead of always treating cycle_tstamp as more recent
96 * than tc->cycle_last, detect when it is too far in the
97 * future and treat it as old time stamp instead.
99 if (cycle_delta
> tc
->cc
->mask
/ 2) {
100 cycle_delta
= (tc
->cycle_last
- cycle_tstamp
) & tc
->cc
->mask
;
101 nsec
= tc
->nsec
- cyclecounter_cyc2ns(tc
->cc
, cycle_delta
);
103 nsec
= cyclecounter_cyc2ns(tc
->cc
, cycle_delta
) + tc
->nsec
;
108 EXPORT_SYMBOL(timecounter_cyc2time
);
110 /*[Clocksource internal variables]---------
112 * currently selected clocksource.
114 * linked list with the registered clocksources
116 * protects manipulations to curr_clocksource and the clocksource_list
118 * Name of the user-specified clocksource.
120 static struct clocksource
*curr_clocksource
;
121 static LIST_HEAD(clocksource_list
);
122 static DEFINE_MUTEX(clocksource_mutex
);
123 static char override_name
[32];
125 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
126 static LIST_HEAD(watchdog_list
);
127 static struct clocksource
*watchdog
;
128 static struct timer_list watchdog_timer
;
129 static struct work_struct watchdog_work
;
130 static DEFINE_SPINLOCK(watchdog_lock
);
131 static cycle_t watchdog_last
;
132 static int watchdog_running
;
134 static int clocksource_watchdog_kthread(void *data
);
135 static void __clocksource_change_rating(struct clocksource
*cs
, int rating
);
138 * Interval: 0.5sec Threshold: 0.0625s
140 #define WATCHDOG_INTERVAL (HZ >> 1)
141 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
143 static void clocksource_watchdog_work(struct work_struct
*work
)
146 * If kthread_run fails the next watchdog scan over the
147 * watchdog_list will find the unstable clock again.
149 kthread_run(clocksource_watchdog_kthread
, NULL
, "kwatchdog");
152 static void __clocksource_unstable(struct clocksource
*cs
)
154 cs
->flags
&= ~(CLOCK_SOURCE_VALID_FOR_HRES
| CLOCK_SOURCE_WATCHDOG
);
155 cs
->flags
|= CLOCK_SOURCE_UNSTABLE
;
156 schedule_work(&watchdog_work
);
159 static void clocksource_unstable(struct clocksource
*cs
, int64_t delta
)
161 printk(KERN_WARNING
"Clocksource %s unstable (delta = %Ld ns)\n",
163 __clocksource_unstable(cs
);
167 * clocksource_mark_unstable - mark clocksource unstable via watchdog
168 * @cs: clocksource to be marked unstable
170 * This function is called instead of clocksource_change_rating from
171 * cpu hotplug code to avoid a deadlock between the clocksource mutex
172 * and the cpu hotplug mutex. It defers the update of the clocksource
173 * to the watchdog thread.
175 void clocksource_mark_unstable(struct clocksource
*cs
)
179 spin_lock_irqsave(&watchdog_lock
, flags
);
180 if (!(cs
->flags
& CLOCK_SOURCE_UNSTABLE
)) {
181 if (list_empty(&cs
->wd_list
))
182 list_add(&cs
->wd_list
, &watchdog_list
);
183 __clocksource_unstable(cs
);
185 spin_unlock_irqrestore(&watchdog_lock
, flags
);
188 static void clocksource_watchdog(unsigned long data
)
190 struct clocksource
*cs
;
191 cycle_t csnow
, wdnow
;
192 int64_t wd_nsec
, cs_nsec
;
195 spin_lock(&watchdog_lock
);
196 if (!watchdog_running
)
199 wdnow
= watchdog
->read(watchdog
);
200 wd_nsec
= clocksource_cyc2ns((wdnow
- watchdog_last
) & watchdog
->mask
,
201 watchdog
->mult
, watchdog
->shift
);
202 watchdog_last
= wdnow
;
204 list_for_each_entry(cs
, &watchdog_list
, wd_list
) {
206 /* Clocksource already marked unstable? */
207 if (cs
->flags
& CLOCK_SOURCE_UNSTABLE
) {
208 schedule_work(&watchdog_work
);
212 csnow
= cs
->read(cs
);
214 /* Clocksource initialized ? */
215 if (!(cs
->flags
& CLOCK_SOURCE_WATCHDOG
)) {
216 cs
->flags
|= CLOCK_SOURCE_WATCHDOG
;
221 /* Check the deviation from the watchdog clocksource. */
222 cs_nsec
= clocksource_cyc2ns((csnow
- cs
->wd_last
) &
223 cs
->mask
, cs
->mult
, cs
->shift
);
225 if (abs(cs_nsec
- wd_nsec
) > WATCHDOG_THRESHOLD
) {
226 clocksource_unstable(cs
, cs_nsec
- wd_nsec
);
230 if (!(cs
->flags
& CLOCK_SOURCE_VALID_FOR_HRES
) &&
231 (cs
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
) &&
232 (watchdog
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
)) {
233 cs
->flags
|= CLOCK_SOURCE_VALID_FOR_HRES
;
235 * We just marked the clocksource as highres-capable,
236 * notify the rest of the system as well so that we
237 * transition into high-res mode:
244 * Cycle through CPUs to check if the CPUs stay synchronized
247 next_cpu
= cpumask_next(raw_smp_processor_id(), cpu_online_mask
);
248 if (next_cpu
>= nr_cpu_ids
)
249 next_cpu
= cpumask_first(cpu_online_mask
);
250 watchdog_timer
.expires
+= WATCHDOG_INTERVAL
;
251 add_timer_on(&watchdog_timer
, next_cpu
);
253 spin_unlock(&watchdog_lock
);
256 static inline void clocksource_start_watchdog(void)
258 if (watchdog_running
|| !watchdog
|| list_empty(&watchdog_list
))
260 INIT_WORK(&watchdog_work
, clocksource_watchdog_work
);
261 init_timer(&watchdog_timer
);
262 watchdog_timer
.function
= clocksource_watchdog
;
263 watchdog_last
= watchdog
->read(watchdog
);
264 watchdog_timer
.expires
= jiffies
+ WATCHDOG_INTERVAL
;
265 add_timer_on(&watchdog_timer
, cpumask_first(cpu_online_mask
));
266 watchdog_running
= 1;
269 static inline void clocksource_stop_watchdog(void)
271 if (!watchdog_running
|| (watchdog
&& !list_empty(&watchdog_list
)))
273 del_timer(&watchdog_timer
);
274 watchdog_running
= 0;
277 static inline void clocksource_reset_watchdog(void)
279 struct clocksource
*cs
;
281 list_for_each_entry(cs
, &watchdog_list
, wd_list
)
282 cs
->flags
&= ~CLOCK_SOURCE_WATCHDOG
;
285 static void clocksource_resume_watchdog(void)
289 spin_lock_irqsave(&watchdog_lock
, flags
);
290 clocksource_reset_watchdog();
291 spin_unlock_irqrestore(&watchdog_lock
, flags
);
294 static void clocksource_enqueue_watchdog(struct clocksource
*cs
)
298 spin_lock_irqsave(&watchdog_lock
, flags
);
299 if (cs
->flags
& CLOCK_SOURCE_MUST_VERIFY
) {
300 /* cs is a clocksource to be watched. */
301 list_add(&cs
->wd_list
, &watchdog_list
);
302 cs
->flags
&= ~CLOCK_SOURCE_WATCHDOG
;
304 /* cs is a watchdog. */
305 if (cs
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
)
306 cs
->flags
|= CLOCK_SOURCE_VALID_FOR_HRES
;
307 /* Pick the best watchdog. */
308 if (!watchdog
|| cs
->rating
> watchdog
->rating
) {
310 /* Reset watchdog cycles */
311 clocksource_reset_watchdog();
314 /* Check if the watchdog timer needs to be started. */
315 clocksource_start_watchdog();
316 spin_unlock_irqrestore(&watchdog_lock
, flags
);
319 static void clocksource_dequeue_watchdog(struct clocksource
*cs
)
321 struct clocksource
*tmp
;
324 spin_lock_irqsave(&watchdog_lock
, flags
);
325 if (cs
->flags
& CLOCK_SOURCE_MUST_VERIFY
) {
326 /* cs is a watched clocksource. */
327 list_del_init(&cs
->wd_list
);
328 } else if (cs
== watchdog
) {
329 /* Reset watchdog cycles */
330 clocksource_reset_watchdog();
331 /* Current watchdog is removed. Find an alternative. */
333 list_for_each_entry(tmp
, &clocksource_list
, list
) {
334 if (tmp
== cs
|| tmp
->flags
& CLOCK_SOURCE_MUST_VERIFY
)
336 if (!watchdog
|| tmp
->rating
> watchdog
->rating
)
340 cs
->flags
&= ~CLOCK_SOURCE_WATCHDOG
;
341 /* Check if the watchdog timer needs to be stopped. */
342 clocksource_stop_watchdog();
343 spin_unlock_irqrestore(&watchdog_lock
, flags
);
346 static int clocksource_watchdog_kthread(void *data
)
348 struct clocksource
*cs
, *tmp
;
352 mutex_lock(&clocksource_mutex
);
353 spin_lock_irqsave(&watchdog_lock
, flags
);
354 list_for_each_entry_safe(cs
, tmp
, &watchdog_list
, wd_list
)
355 if (cs
->flags
& CLOCK_SOURCE_UNSTABLE
) {
356 list_del_init(&cs
->wd_list
);
357 list_add(&cs
->wd_list
, &unstable
);
359 /* Check if the watchdog timer needs to be stopped. */
360 clocksource_stop_watchdog();
361 spin_unlock_irqrestore(&watchdog_lock
, flags
);
363 /* Needs to be done outside of watchdog lock */
364 list_for_each_entry_safe(cs
, tmp
, &unstable
, wd_list
) {
365 list_del_init(&cs
->wd_list
);
366 __clocksource_change_rating(cs
, 0);
368 mutex_unlock(&clocksource_mutex
);
372 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */
374 static void clocksource_enqueue_watchdog(struct clocksource
*cs
)
376 if (cs
->flags
& CLOCK_SOURCE_IS_CONTINUOUS
)
377 cs
->flags
|= CLOCK_SOURCE_VALID_FOR_HRES
;
380 static inline void clocksource_dequeue_watchdog(struct clocksource
*cs
) { }
381 static inline void clocksource_resume_watchdog(void) { }
383 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
386 * clocksource_resume - resume the clocksource(s)
388 void clocksource_resume(void)
390 struct clocksource
*cs
;
392 mutex_lock(&clocksource_mutex
);
394 list_for_each_entry(cs
, &clocksource_list
, list
)
398 clocksource_resume_watchdog();
400 mutex_unlock(&clocksource_mutex
);
404 * clocksource_touch_watchdog - Update watchdog
406 * Update the watchdog after exception contexts such as kgdb so as not
407 * to incorrectly trip the watchdog.
410 void clocksource_touch_watchdog(void)
412 clocksource_resume_watchdog();
415 #ifdef CONFIG_GENERIC_TIME
417 static int finished_booting
;
420 * clocksource_select - Select the best clocksource available
422 * Private function. Must hold clocksource_mutex when called.
424 * Select the clocksource with the best rating, or the clocksource,
425 * which is selected by userspace override.
427 static void clocksource_select(void)
429 struct clocksource
*best
, *cs
;
431 if (!finished_booting
|| list_empty(&clocksource_list
))
433 /* First clocksource on the list has the best rating. */
434 best
= list_first_entry(&clocksource_list
, struct clocksource
, list
);
435 /* Check for the override clocksource. */
436 list_for_each_entry(cs
, &clocksource_list
, list
) {
437 if (strcmp(cs
->name
, override_name
) != 0)
440 * Check to make sure we don't switch to a non-highres
441 * capable clocksource if the tick code is in oneshot
442 * mode (highres or nohz)
444 if (!(cs
->flags
& CLOCK_SOURCE_VALID_FOR_HRES
) &&
445 tick_oneshot_mode_active()) {
446 /* Override clocksource cannot be used. */
447 printk(KERN_WARNING
"Override clocksource %s is not "
448 "HRT compatible. Cannot switch while in "
449 "HRT/NOHZ mode\n", cs
->name
);
450 override_name
[0] = 0;
452 /* Override clocksource can be used. */
456 if (curr_clocksource
!= best
) {
457 printk(KERN_INFO
"Switching to clocksource %s\n", best
->name
);
458 curr_clocksource
= best
;
459 timekeeping_notify(curr_clocksource
);
464 * clocksource_done_booting - Called near the end of core bootup
466 * Hack to avoid lots of clocksource churn at boot time.
467 * We use fs_initcall because we want this to start before
468 * device_initcall but after subsys_initcall.
470 static int __init
clocksource_done_booting(void)
472 finished_booting
= 1;
473 clocksource_select();
476 fs_initcall(clocksource_done_booting
);
478 #else /* CONFIG_GENERIC_TIME */
480 static inline void clocksource_select(void) { }
485 * Enqueue the clocksource sorted by rating
487 static void clocksource_enqueue(struct clocksource
*cs
)
489 struct list_head
*entry
= &clocksource_list
;
490 struct clocksource
*tmp
;
492 list_for_each_entry(tmp
, &clocksource_list
, list
)
493 /* Keep track of the place, where to insert */
494 if (tmp
->rating
>= cs
->rating
)
496 list_add(&cs
->list
, entry
);
500 * clocksource_register - Used to install new clocksources
501 * @t: clocksource to be registered
503 * Returns -EBUSY if registration fails, zero otherwise.
505 int clocksource_register(struct clocksource
*cs
)
507 mutex_lock(&clocksource_mutex
);
508 clocksource_enqueue(cs
);
509 clocksource_select();
510 clocksource_enqueue_watchdog(cs
);
511 mutex_unlock(&clocksource_mutex
);
514 EXPORT_SYMBOL(clocksource_register
);
516 static void __clocksource_change_rating(struct clocksource
*cs
, int rating
)
520 clocksource_enqueue(cs
);
521 clocksource_select();
525 * clocksource_change_rating - Change the rating of a registered clocksource
527 void clocksource_change_rating(struct clocksource
*cs
, int rating
)
529 mutex_lock(&clocksource_mutex
);
530 __clocksource_change_rating(cs
, rating
);
531 mutex_unlock(&clocksource_mutex
);
533 EXPORT_SYMBOL(clocksource_change_rating
);
536 * clocksource_unregister - remove a registered clocksource
538 void clocksource_unregister(struct clocksource
*cs
)
540 mutex_lock(&clocksource_mutex
);
541 clocksource_dequeue_watchdog(cs
);
543 clocksource_select();
544 mutex_unlock(&clocksource_mutex
);
546 EXPORT_SYMBOL(clocksource_unregister
);
550 * sysfs_show_current_clocksources - sysfs interface for current clocksource
552 * @buf: char buffer to be filled with clocksource list
554 * Provides sysfs interface for listing current clocksource.
557 sysfs_show_current_clocksources(struct sys_device
*dev
,
558 struct sysdev_attribute
*attr
, char *buf
)
562 mutex_lock(&clocksource_mutex
);
563 count
= snprintf(buf
, PAGE_SIZE
, "%s\n", curr_clocksource
->name
);
564 mutex_unlock(&clocksource_mutex
);
570 * sysfs_override_clocksource - interface for manually overriding clocksource
572 * @buf: name of override clocksource
573 * @count: length of buffer
575 * Takes input from sysfs interface for manually overriding the default
576 * clocksource selction.
578 static ssize_t
sysfs_override_clocksource(struct sys_device
*dev
,
579 struct sysdev_attribute
*attr
,
580 const char *buf
, size_t count
)
584 /* strings from sysfs write are not 0 terminated! */
585 if (count
>= sizeof(override_name
))
589 if (buf
[count
-1] == '\n')
592 mutex_lock(&clocksource_mutex
);
595 memcpy(override_name
, buf
, count
);
596 override_name
[count
] = 0;
597 clocksource_select();
599 mutex_unlock(&clocksource_mutex
);
605 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
607 * @buf: char buffer to be filled with clocksource list
609 * Provides sysfs interface for listing registered clocksources
612 sysfs_show_available_clocksources(struct sys_device
*dev
,
613 struct sysdev_attribute
*attr
,
616 struct clocksource
*src
;
619 mutex_lock(&clocksource_mutex
);
620 list_for_each_entry(src
, &clocksource_list
, list
) {
622 * Don't show non-HRES clocksource if the tick code is
623 * in one shot mode (highres=on or nohz=on)
625 if (!tick_oneshot_mode_active() ||
626 (src
->flags
& CLOCK_SOURCE_VALID_FOR_HRES
))
627 count
+= snprintf(buf
+ count
,
628 max((ssize_t
)PAGE_SIZE
- count
, (ssize_t
)0),
631 mutex_unlock(&clocksource_mutex
);
633 count
+= snprintf(buf
+ count
,
634 max((ssize_t
)PAGE_SIZE
- count
, (ssize_t
)0), "\n");
642 static SYSDEV_ATTR(current_clocksource
, 0644, sysfs_show_current_clocksources
,
643 sysfs_override_clocksource
);
645 static SYSDEV_ATTR(available_clocksource
, 0444,
646 sysfs_show_available_clocksources
, NULL
);
648 static struct sysdev_class clocksource_sysclass
= {
649 .name
= "clocksource",
652 static struct sys_device device_clocksource
= {
654 .cls
= &clocksource_sysclass
,
657 static int __init
init_clocksource_sysfs(void)
659 int error
= sysdev_class_register(&clocksource_sysclass
);
662 error
= sysdev_register(&device_clocksource
);
664 error
= sysdev_create_file(
666 &attr_current_clocksource
);
668 error
= sysdev_create_file(
670 &attr_available_clocksource
);
674 device_initcall(init_clocksource_sysfs
);
675 #endif /* CONFIG_SYSFS */
678 * boot_override_clocksource - boot clock override
679 * @str: override name
681 * Takes a clocksource= boot argument and uses it
682 * as the clocksource override name.
684 static int __init
boot_override_clocksource(char* str
)
686 mutex_lock(&clocksource_mutex
);
688 strlcpy(override_name
, str
, sizeof(override_name
));
689 mutex_unlock(&clocksource_mutex
);
693 __setup("clocksource=", boot_override_clocksource
);
696 * boot_override_clock - Compatibility layer for deprecated boot option
697 * @str: override name
699 * DEPRECATED! Takes a clock= boot argument and uses it
700 * as the clocksource override name
702 static int __init
boot_override_clock(char* str
)
704 if (!strcmp(str
, "pmtmr")) {
705 printk("Warning: clock=pmtmr is deprecated. "
706 "Use clocksource=acpi_pm.\n");
707 return boot_override_clocksource("acpi_pm");
709 printk("Warning! clock= boot option is deprecated. "
710 "Use clocksource=xyz\n");
711 return boot_override_clocksource(str
);
714 __setup("clock=", boot_override_clock
);