summaryrefslogtreecommitdiffstats
path: root/kernel/time/clockevents.c
blob: 50eb107f119877ab0762bb671a69cf9c0cd418bc (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
/*
 * linux/kernel/time/clockevents.c
 *
 * This file contains functions which manage clock event devices.
 *
 * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
 * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
 *
 * This code is licenced under the GPL version 2. For details see
 * kernel-base/COPYING.
 */

#include <linux/clockchips.h>
#include <linux/hrtimer.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/smp.h>
#include <linux/device.h>

#include "tick-internal.h"

/* The registered clock event devices */
static LIST_HEAD(clockevent_devices);
static LIST_HEAD(clockevents_released);
/* Protection for the above */
static DEFINE_RAW_SPINLOCK(clockevents_lock);
/* Protection for unbind operations */
static DEFINE_MUTEX(clockevents_mutex);

struct ce_unbind {
	struct clock_event_device *ce;
	int res;
};

static u64 cev_delta2ns(unsigned long latch, struct clock_event_device *evt,
			bool ismax)
{
	u64 clc = (u64) latch << evt->shift;
	u64 rnd;

	if (unlikely(!evt->mult)) {
		evt->mult = 1;
		WARN_ON(1);
	}
	rnd = (u64) evt->mult - 1;

	/*
	 * Upper bound sanity check. If the backwards conversion is
	 * not equal latch, we know that the above shift overflowed.
	 */
	if ((clc >> evt->shift) != (u64)latch)
		clc = ~0ULL;

	/*
	 * Scaled math oddities:
	 *
	 * For mult <= (1 << shift) we can safely add mult - 1 to
	 * prevent integer rounding loss. So the backwards conversion
	 * from nsec to device ticks will be correct.
	 *
	 * For mult > (1 << shift), i.e. device frequency is > 1GHz we
	 * need to be careful. Adding mult - 1 will result in a value
	 * which when converted back to device ticks can be larger
	 * than latch by up to (mult - 1) >> shift. For the min_delta
	 * calculation we still want to apply this in order to stay
	 * above the minimum device ticks limit. For the upper limit
	 * we would end up with a latch value larger than the upper
	 * limit of the device, so we omit the add to stay below the
	 * device upper boundary.
	 *
	 * Also omit the add if it would overflow the u64 boundary.
	 */
	if ((~0ULL - clc > rnd) &&
	    (!ismax || evt->mult <= (1ULL << evt->shift)))
		clc += rnd;

	do_div(clc, evt->mult);

	/* Deltas less than 1usec are pointless noise */
	return clc > 1000 ? clc : 1000;
}

/**
 * clockevents_delta2ns - Convert a latch value (device ticks) to nanoseconds
 * @latch:	value to convert
 * @evt:	pointer to clock event device descriptor
 *
 * Math helper, returns latch value converted to nanoseconds (bound checked)
 */
u64 clockevent_delta2ns(unsigned long latch, struct clock_event_device *evt)
{
	return cev_delta2ns(latch, evt, false);
}
EXPORT_SYMBOL_GPL(clockevent_delta2ns);

static int __clockevents_switch_state(struct clock_event_device *dev,
				      enum clock_event_state state)
{
	/* Transition with legacy set_mode() callback */
	if (dev->set_mode) {
		/* Legacy callback doesn't support new modes */
		if (state > CLOCK_EVT_STATE_ONESHOT)
			return -ENOSYS;
		/*
		 * 'clock_event_state' and 'clock_event_mode' have 1-to-1
		 * mapping until *_ONESHOT, and so a simple cast will work.
		 */
		dev->set_mode((enum clock_event_mode)state, dev);
		dev->mode = (enum clock_event_mode)state;
		return 0;
	}

	if (dev->features & CLOCK_EVT_FEAT_DUMMY)
		return 0;

	/* Transition with new state-specific callbacks */
	switch (state) {
	case CLOCK_EVT_STATE_DETACHED:
		/* The clockevent device is getting replaced. Shut it down. */

	case CLOCK_EVT_STATE_SHUTDOWN:
		if (dev->set_state_shutdown)
			return dev->set_state_shutdown(dev);
		return 0;

	case CLOCK_EVT_STATE_PERIODIC:
		/* Core internal bug */
		if (!(dev->features & CLOCK_EVT_FEAT_PERIODIC))
			return -ENOSYS;
		if (dev->set_state_periodic)
			return dev->set_state_periodic(dev);
		return 0;

	case CLOCK_EVT_STATE_ONESHOT:
		/* Core internal bug */
		if (!(dev->features & CLOCK_EVT_FEAT_ONESHOT))
			return -ENOSYS;
		if (dev->set_state_oneshot)
			return dev->set_state_oneshot(dev);
		return 0;

	case CLOCK_EVT_STATE_ONESHOT_STOPPED:
		/* Core internal bug */
		if (WARN_ONCE(!clockevent_state_oneshot(dev),
			      "Current state: %d\n",
			      clockevent_get_state(dev)))
			return -EINVAL;

		if (dev->set_state_oneshot_stopped)
			return dev->set_state_oneshot_stopped(dev);
		else
			return -ENOSYS;

	default:
		return -ENOSYS;
	}
}

/**
 * clockevents_switch_state - set the operating state of a clock event device
 * @dev:	device to modify
 * @state:	new state
 *
 * Must be called with interrupts disabled !
 */
void clockevents_switch_state(struct clock_event_device *dev,
			      enum clock_event_state state)
{
	if (clockevent_get_state(dev) != state) {
		if (__clockevents_switch_state(dev, state))
			return;

		clockevent_set_state(dev, state);

		/*
		 * A nsec2cyc multiplicator of 0 is invalid and we'd crash
		 * on it, so fix it up and emit a warning:
		 */
		if (clockevent_state_oneshot(dev)) {
			if (unlikely(!dev->mult)) {
				dev->mult = 1;
				WARN_ON(1);
			}
		}
	}
}

/**
 * clockevents_shutdown - shutdown the device and clear next_event
 * @dev:	device to shutdown
 */
void clockevents_shutdown(struct clock_event_device *dev)
{
	clockevents_switch_state(dev, CLOCK_EVT_STATE_SHUTDOWN);
	dev->next_event.tv64 = KTIME_MAX;
}

/**
 * clockevents_tick_resume -	Resume the tick device before using it again
 * @dev:			device to resume
 */
int clockevents_tick_resume(struct clock_event_device *dev)
{
	int ret = 0;

	if (dev->set_mode) {
		dev->set_mode(CLOCK_EVT_MODE_RESUME, dev);
		dev->mode = CLOCK_EVT_MODE_RESUME;
	} else if (dev->tick_resume) {
		ret = dev->tick_resume(dev);
	}

	return ret;
}

#ifdef CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST

/* Limit min_delta to a jiffie */
#define MIN_DELTA_LIMIT		(NSEC_PER_SEC / HZ)

/**
 * clockevents_increase_min_delta - raise minimum delta of a clock event device
 * @dev:       device to increase the minimum delta
 *
 * Returns 0 on success, -ETIME when the minimum delta reached the limit.
 */
static int clockevents_increase_min_delta(struct clock_event_device *dev)
{
	/* Nothing to do if we already reached the limit */
	if (dev->min_delta_ns >= MIN_DELTA_LIMIT) {
		printk_deferred(KERN_WARNING
				"CE: Reprogramming failure. Giving up\n");
		dev->next_event.tv64 = KTIME_MAX;
		return -ETIME;
	}

	if (dev->min_delta_ns < 5000)
		dev->min_delta_ns = 5000;
	else
		dev->min_delta_ns += dev->min_delta_ns >> 1;

	if (dev->min_delta_ns > MIN_DELTA_LIMIT)
		dev->min_delta_ns = MIN_DELTA_LIMIT;

	printk_deferred(KERN_WARNING
			"CE: %s increased min_delta_ns to %llu nsec\n",
			dev->name ? dev->name : "?",
			(unsigned long long) dev->min_delta_ns);
	return 0;
}

/**
 * clockevents_program_min_delta - Set clock event device to the minimum delay.
 * @dev:	device to program
 *
 * Returns 0 on success, -ETIME when the retry loop failed.
 */
static int clockevents_program_min_delta(struct clock_event_device *dev)
{
	unsigned long long clc;
	int64_t delta;
	int i;

	for (i = 0;;) {
		delta = dev->min_delta_ns;
		dev->next_event = ktime_add_ns(ktime_get(), delta);

		if (clockevent_state_shutdown(dev))
			return 0;

		dev->retries++;
		clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
		if (dev->set_next_event((unsigned long) clc, dev) == 0)
			return 0;

		if (++i > 2) {
			/*
			 * We tried 3 times to program the device with the
			 * given min_delta_ns. Try to increase the minimum
			 * delta, if that fails as well get out of here.
			 */
			if (clockevents_increase_min_delta(dev))
				return -ETIME;
			i = 0;
		}
	}
}

#else  /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */

/**
 * clockevents_program_min_delta - Set clock event device to the minimum delay.
 * @dev:	device to program
 *
 * Returns 0 on success, -ETIME when the retry loop failed.
 */
static int clockevents_program_min_delta(struct clock_event_device *dev)
{
	unsigned long long clc;
	int64_t delta;

	delta = dev->min_delta_ns;
	dev->next_event = ktime_add_ns(ktime_get(), delta);

	if (clockevent_state_shutdown(dev))
		return 0;

	dev->retries++;
	clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
	return dev->set_next_event((unsigned long) clc, dev);
}

#endif /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */

/**
 * clockevents_program_event - Reprogram the clock event device.
 * @dev:	device to program
 * @expires:	absolute expiry time (monotonic clock)
 * @force:	program minimum delay if expires can not be set
 *
 * Returns 0 on success, -ETIME when the event is in the past.
 */
int clockevents_program_event(struct clock_event_device *dev, ktime_t expires,
			      bool force)
{
	unsigned long long clc;
	int64_t delta;
	int rc;

	if (unlikely(expires.tv64 < 0)) {
		WARN_ON_ONCE(1);
		return -ETIME;
	}

	dev->next_event = expires;

	if (clockevent_state_shutdown(dev))
		return 0;

	/* We must be in ONESHOT state here */
	WARN_ONCE(!clockevent_state_oneshot(dev), "Current state: %d\n",
		  clockevent_get_state(dev));

	/* Shortcut for clockevent devices that can deal with ktime. */
	if (dev->features & CLOCK_EVT_FEAT_KTIME)
		return dev->set_next_ktime(expires, dev);

	delta = ktime_to_ns(ktime_sub(expires, ktime_get()));
	if (delta <= 0)
		return force ? clockevents_program_min_delta(dev) : -ETIME;

	delta = min(delta, (int64_t) dev->max_delta_ns);
	delta = max(delta, (int64_t) dev->min_delta_ns);

	clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
	rc = dev->set_next_event((unsigned long) clc, dev);

	return (rc && force) ? clockevents_program_min_delta(dev) : rc;
}

/*
 * Called after a notify add to make devices available which were
 * released from the notifier call.
 */
static void clockevents_notify_released(void)
{
	struct clock_event_device *dev;

	while (!list_empty(&clockevents_released)) {
		dev = list_entry(clockevents_released.next,
				 struct clock_event_device, list);
		list_del(&dev->list);
		list_add(&dev->list, &clockevent_devices);
		tick_check_new_device(dev);
	}
}

/*
 * Try to install a replacement clock event device
 */
static int clockevents_replace(struct clock_event_device *ced)
{
	struct clock_event_device *dev, *newdev = NULL;

	list_for_each_entry(dev, &clockevent_devices, list) {
		if (dev == ced || !clockevent_state_detached(dev))
			continue;

		if (!tick_check_replacement(newdev, dev))
			continue;

		if (!try_module_get(dev->owner))
			continue;

		if (newdev)
			module_put(newdev->owner);
		newdev = dev;
	}
	if (newdev) {
		tick_install_replacement(newdev);
		list_del_init(&ced->list);
	}
	return newdev ? 0 : -EBUSY;
}

/*
 * Called with clockevents_mutex and clockevents_lock held
 */
static int __clockevents_try_unbind(struct clock_event_device *ced, int cpu)
{
	/* Fast track. Device is unused */
	if (clockevent_state_detached(ced)) {
		list_del_init(&ced->list);
		return 0;
	}

	return ced == per_cpu(tick_cpu_device, cpu).evtdev ? -EAGAIN : -EBUSY;
}

/*
 * SMP function call to unbind a device
 */
static void __clockevents_unbind(void *arg)
{
	struct ce_unbind *cu = arg;
	int res;

	raw_spin_lock(&clockevents_lock);
	res = __clockevents_try_unbind(cu->ce, smp_processor_id());
	if (res == -EAGAIN)
		res = clockevents_replace(cu->ce);
	cu->res = res;
	raw_spin_unlock(&clockevents_lock);
}

/*
 * Issues smp function call to unbind a per cpu device. Called with
 * clockevents_mutex held.
 */
static int clockevents_unbind(struct clock_event_device *ced, int cpu)
{
	struct ce_unbind cu = { .ce = ced, .res = -ENODEV };

	smp_call_function_single(cpu, __clockevents_unbind, &cu, 1);
	return cu.res;
}

/*
 * Unbind a clockevents device.
 */
int clockevents_unbind_device(struct clock_event_device *ced, int cpu)
{
	int ret;

	mutex_lock(&clockevents_mutex);
	ret = clockevents_unbind(ced, cpu);
	mutex_unlock(&clockevents_mutex);
	return ret;
}
EXPORT_SYMBOL_GPL(clockevents_unbind_device);

/* Sanity check of state transition callbacks */
static int clockevents_sanity_check(struct clock_event_device *dev)
{
	/* Legacy set_mode() callback */
	if (dev->set_mode) {
		/* We shouldn't be supporting new modes now */
		WARN_ON(dev->set_state_periodic || dev->set_state_oneshot ||
			dev->set_state_shutdown || dev->tick_resume ||
			dev->set_state_oneshot_stopped);

		BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);
		return 0;
	}

	if (dev->features & CLOCK_EVT_FEAT_DUMMY)
		return 0;

	return 0;
}

/**
 * clockevents_register_device - register a clock event device
 * @dev:	device to register
 */
void clockevents_register_device(struct clock_event_device *dev)
{
	unsigned long flags;

	BUG_ON(clockevents_sanity_check(dev));

	/* Initialize state to DETACHED */
	clockevent_set_state(dev, CLOCK_EVT_STATE_DETACHED);

	if (!dev->cpumask) {
		WARN_ON(num_possible_cpus() > 1);
		dev->cpumask = cpumask_of(smp_processor_id());
	}

	raw_spin_lock_irqsave(&clockevents_lock, flags);

	list_add(&dev->list, &clockevent_devices);
	tick_check_new_device(dev);
	clockevents_notify_released();

	raw_spin_unlock_irqrestore(&clockevents_lock, flags);
}
EXPORT_SYMBOL_GPL(clockevents_register_device);

void clockevents_config(struct clock_event_device *dev, u32 freq)
{
	u64 sec;

	if (!(dev->features & CLOCK_EVT_FEAT_ONESHOT))
		return;

	/*
	 * Calculate the maximum number of seconds we can sleep. Limit
	 * to 10 minutes for hardware which can program more than
	 * 32bit ticks so we still get reasonable conversion values.
	 */
	sec = dev->max_delta_ticks;
	do_div(sec, freq);
	if (!sec)
		sec = 1;
	else if (sec > 600 && dev->max_delta_ticks > UINT_MAX)
		sec = 600;

	clockevents_calc_mult_shift(dev, freq, sec);
	dev->min_delta_ns = cev_delta2ns(dev->min_delta_ticks, dev, false);
	dev->max_delta_ns = cev_delta2ns(dev->max_delta_ticks, dev, true);
}

/**
 * clockevents_config_and_register - Configure and register a clock event device
 * @dev:	device to register
 * @freq:	The clock frequency
 * @min_delta:	The minimum clock ticks to program in oneshot mode
 * @max_delta:	The maximum clock ticks to program in oneshot mode
 *
 * min/max_delta can be 0 for devices which do not support oneshot mode.
 */
void clockevents_config_and_register(struct clock_event_device *dev,
				     u32 freq, unsigned long min_delta,
				     unsigned long max_delta)
{
	dev->min_delta_ticks = min_delta;
	dev->max_delta_ticks = max_delta;
	clockevents_config(dev, freq);
	clockevents_register_device(dev);
}
EXPORT_SYMBOL_GPL(clockevents_config_and_register);

int __clockevents_update_freq(struct clock_event_device *dev, u32 freq)
{
	clockevents_config(dev, freq);

	if (clockevent_state_oneshot(dev))
		return clockevents_program_event(dev, dev->next_event, false);

	if (clockevent_state_periodic(dev))
		return __clockevents_switch_state(dev, CLOCK_EVT_STATE_PERIODIC);

	return 0;
}

/**
 * clockevents_update_freq - Update frequency and reprogram a clock event device.
 * @dev:	device to modify
 * @freq:	new device frequency
 *
 * Reconfigure and reprogram a clock event device in oneshot
 * mode. Must be called on the cpu for which the device delivers per
 * cpu timer events. If called for the broadcast device the core takes
 * care of serialization.
 *
 * Returns 0 on success, -ETIME when the event is in the past.
 */
int clockevents_update_freq(struct clock_event_device *dev, u32 freq)
{
	unsigned long flags;
	int ret;

	local_irq_save(flags);
	ret = tick_broadcast_update_freq(dev, freq);
	if (ret == -ENODEV)
		ret = __clockevents_update_freq(dev, freq);
	local_irq_restore(flags);
	return ret;
}

/*
 * Noop handler when we shut down an event device
 */
void clockevents_handle_noop(struct clock_event_device *dev)
{
}

/**
 * clockevents_exchange_device - release and request clock devices
 * @old:	device to release (can be NULL)
 * @new:	device to request (can be NULL)
 *
 * Called from various tick functions with clockevents_lock held and
 * interrupts disabled.
 */
void clockevents_exchange_device(struct clock_event_device *old,
				 struct clock_event_device *new)
{
	/*
	 * Caller releases a clock event device. We queue it into the
	 * released list and do a notify add later.
	 */
	if (old) {
		module_put(old->owner);
		clockevents_switch_state(old, CLOCK_EVT_STATE_DETACHED);
		list_del(&old->list);
		list_add(&old->list, &clockevents_released);
	}

	if (new) {
		BUG_ON(!clockevent_state_detached(new));
		clockevents_shutdown(new);
	}
}

/**
 * clockevents_suspend - suspend clock devices
 */
void clockevents_suspend(void)
{
	struct clock_event_device *dev;

	list_for_each_entry_reverse(dev, &clockevent_devices, list)
		if (dev->suspend && !clockevent_state_detached(dev))
			dev->suspend(dev);
}

/**
 * clockevents_resume - resume clock devices
 */
void clockevents_resume(void)
{
	struct clock_event_device *dev;

	list_for_each_entry(dev, &clockevent_devices, list)
		if (dev->resume && !clockevent_state_detached(dev))
			dev->resume(dev);
}

#ifdef CONFIG_HOTPLUG_CPU
/**
 * tick_cleanup_dead_cpu - Cleanup the tick and clockevents of a dead cpu
 */
void tick_cleanup_dead_cpu(int cpu)
{
	struct clock_event_device *dev, *tmp;
	unsigned long flags;

	raw_spin_lock_irqsave(&clockevents_lock, flags);

	tick_shutdown_broadcast_oneshot(cpu);
	tick_shutdown_broadcast(cpu);
	tick_shutdown(cpu);
	/*
	 * Unregister the clock event devices which were
	 * released from the users in the notify chain.
	 */
	list_for_each_entry_safe(dev, tmp, &clockevents_released, list)
		list_del(&dev->list);
	/*
	 * Now check whether the CPU has left unused per cpu devices
	 */
	list_for_each_entry_safe(dev, tmp, &clockevent_devices, list) {
		if (cpumask_test_cpu(cpu, dev->cpumask) &&
		    cpumask_weight(dev->cpumask) == 1 &&
		    !tick_is_broadcast_device(dev)) {
			BUG_ON(!clockevent_state_detached(dev));
			list_del(&dev->list);
		}
	}
	raw_spin_unlock_irqrestore(&clockevents_lock, flags);
}
#endif

#ifdef CONFIG_SYSFS
struct bus_type clockevents_subsys = {
	.name		= "clockevents",
	.dev_name       = "clockevent",
};

static DEFINE_PER_CPU(struct device, tick_percpu_dev);
static struct tick_device *tick_get_tick_dev(struct device *dev);

static ssize_t sysfs_show_current_tick_dev(struct device *dev,
					   struct device_attribute *attr,
					   char *buf)
{
	struct tick_device *td;
	ssize_t count = 0;

	raw_spin_lock_irq(&clockevents_lock);
	td = tick_get_tick_dev(dev);
	if (td && td->evtdev)
		count = snprintf(buf, PAGE_SIZE, "%s\n", td->evtdev->name);
	raw_spin_unlock_irq(&clockevents_lock);
	return count;
}
static DEVICE_ATTR(current_device, 0444, sysfs_show_current_tick_dev, NULL);

/* We don't support the abomination of removable broadcast devices */
static ssize_t sysfs_unbind_tick_dev(struct device *dev,
				     struct device_attribute *attr,
				     const char *buf, size_t count)
{
	char name[CS_NAME_LEN];
	ssize_t ret = sysfs_get_uname(buf, name, count);
	struct clock_event_device *ce;

	if (ret < 0)
		return ret;

	ret = -ENODEV;
	mutex_lock(&clockevents_mutex);
	raw_spin_lock_irq(&clockevents_lock);
	list_for_each_entry(ce, &clockevent_devices, list) {
		if (!strcmp(ce->name, name)) {
			ret = __clockevents_try_unbind(ce, dev->id);
			break;
		}
	}
	raw_spin_unlock_irq(&clockevents_lock);
	/*
	 * We hold clockevents_mutex, so ce can't go away
	 */
	if (ret == -EAGAIN)
		ret = clockevents_unbind(ce, dev->id);
	mutex_unlock(&clockevents_mutex);
	return ret ? ret : count;
}
static DEVICE_ATTR(unbind_device, 0200, NULL, sysfs_unbind_tick_dev);

#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
static struct device tick_bc_dev = {
	.init_name	= "broadcast",
	.id		= 0,
	.bus		= &clockevents_subsys,
};

static struct tick_device *tick_get_tick_dev(struct device *dev)
{
	return dev == &tick_bc_dev ? tick_get_broadcast_device() :
		&per_cpu(tick_cpu_device, dev->id);
}

static __init int tick_broadcast_init_sysfs(void)
{
	int err = device_register(&tick_bc_dev);

	if (!err)
		err = device_create_file(&tick_bc_dev, &dev_attr_current_device);
	return err;
}
#else
static struct tick_device *tick_get_tick_dev(struct device *dev)
{
	return &per_cpu(tick_cpu_device, dev->id);
}
static inline int tick_broadcast_init_sysfs(void) { return 0; }
#endif

static int __init tick_init_sysfs(void)
{
	int cpu;

	for_each_possible_cpu(cpu) {
		struct device *dev = &per_cpu(tick_percpu_dev, cpu);
		int err;

		dev->id = cpu;
		dev->bus = &clockevents_subsys;
		err = device_register(dev);
		if (!err)
			err = device_create_file(dev, &dev_attr_current_device);
		if (!err)
			err = device_create_file(dev, &dev_attr_unbind_device);
		if (err)
			return err;
	}
	return tick_broadcast_init_sysfs();
}

static int __init clockevents_init_sysfs(void)
{
	int err = subsys_system_register(&clockevents_subsys, NULL);

	if (!err)
		err = tick_init_sysfs();
	return err;
}
device_initcall(clockevents_init_sysfs);
#endif /* SYSFS */