summaryrefslogtreecommitdiff
path: root/kernel/time/clocksource.c
blob: 1cf73807b4503b982cbcaa835f0a4ba9ffd17d50 (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
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
// SPDX-License-Identifier: GPL-2.0+
/*
 * This file contains the functions which manage clocksource drivers.
 *
 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/device.h>
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
#include <linux/tick.h>
#include <linux/kthread.h>
#include <linux/prandom.h>
#include <linux/cpu.h>

#include "tick-internal.h"
#include "timekeeping_internal.h"

/**
 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
 * @mult:	pointer to mult variable
 * @shift:	pointer to shift variable
 * @from:	frequency to convert from
 * @to:		frequency to convert to
 * @maxsec:	guaranteed runtime conversion range in seconds
 *
 * The function evaluates the shift/mult pair for the scaled math
 * operations of clocksources and clockevents.
 *
 * @to and @from are frequency values in HZ. For clock sources @to is
 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
 * event @to is the counter frequency and @from is NSEC_PER_SEC.
 *
 * The @maxsec conversion range argument controls the time frame in
 * seconds which must be covered by the runtime conversion with the
 * calculated mult and shift factors. This guarantees that no 64bit
 * overflow happens when the input value of the conversion is
 * multiplied with the calculated mult factor. Larger ranges may
 * reduce the conversion accuracy by choosing smaller mult and shift
 * factors.
 */
void
clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
{
	u64 tmp;
	u32 sft, sftacc= 32;

	/*
	 * Calculate the shift factor which is limiting the conversion
	 * range:
	 */
	tmp = ((u64)maxsec * from) >> 32;
	while (tmp) {
		tmp >>=1;
		sftacc--;
	}

	/*
	 * Find the conversion shift/mult pair which has the best
	 * accuracy and fits the maxsec conversion range:
	 */
	for (sft = 32; sft > 0; sft--) {
		tmp = (u64) to << sft;
		tmp += from / 2;
		do_div(tmp, from);
		if ((tmp >> sftacc) == 0)
			break;
	}
	*mult = tmp;
	*shift = sft;
}
EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);

/*[Clocksource internal variables]---------
 * curr_clocksource:
 *	currently selected clocksource.
 * suspend_clocksource:
 *	used to calculate the suspend time.
 * clocksource_list:
 *	linked list with the registered clocksources
 * clocksource_mutex:
 *	protects manipulations to curr_clocksource and the clocksource_list
 * override_name:
 *	Name of the user-specified clocksource.
 */
static struct clocksource *curr_clocksource;
static struct clocksource *suspend_clocksource;
static LIST_HEAD(clocksource_list);
static DEFINE_MUTEX(clocksource_mutex);
static char override_name[CS_NAME_LEN];
static int finished_booting;
static u64 suspend_start;

/*
 * Threshold: 0.0312s, when doubled: 0.0625s.
 * Also a default for cs->uncertainty_margin when registering clocks.
 */
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5)

/*
 * Maximum permissible delay between two readouts of the watchdog
 * clocksource surrounding a read of the clocksource being validated.
 * This delay could be due to SMIs, NMIs, or to VCPU preemptions.  Used as
 * a lower bound for cs->uncertainty_margin values when registering clocks.
 */
#define WATCHDOG_MAX_SKEW (100 * NSEC_PER_USEC)

#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
static void clocksource_watchdog_work(struct work_struct *work);
static void clocksource_select(void);

static LIST_HEAD(watchdog_list);
static struct clocksource *watchdog;
static struct timer_list watchdog_timer;
static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
static DEFINE_SPINLOCK(watchdog_lock);
static int watchdog_running;
static atomic_t watchdog_reset_pending;

static inline void clocksource_watchdog_lock(unsigned long *flags)
{
	spin_lock_irqsave(&watchdog_lock, *flags);
}

static inline void clocksource_watchdog_unlock(unsigned long *flags)
{
	spin_unlock_irqrestore(&watchdog_lock, *flags);
}

static int clocksource_watchdog_kthread(void *data);
static void __clocksource_change_rating(struct clocksource *cs, int rating);

/*
 * Interval: 0.5sec.
 */
#define WATCHDOG_INTERVAL (HZ >> 1)

static void clocksource_watchdog_work(struct work_struct *work)
{
	/*
	 * We cannot directly run clocksource_watchdog_kthread() here, because
	 * clocksource_select() calls timekeeping_notify() which uses
	 * stop_machine(). One cannot use stop_machine() from a workqueue() due
	 * lock inversions wrt CPU hotplug.
	 *
	 * Also, we only ever run this work once or twice during the lifetime
	 * of the kernel, so there is no point in creating a more permanent
	 * kthread for this.
	 *
	 * If kthread_run fails the next watchdog scan over the
	 * watchdog_list will find the unstable clock again.
	 */
	kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
}

static void __clocksource_unstable(struct clocksource *cs)
{
	cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
	cs->flags |= CLOCK_SOURCE_UNSTABLE;

	/*
	 * If the clocksource is registered clocksource_watchdog_kthread() will
	 * re-rate and re-select.
	 */
	if (list_empty(&cs->list)) {
		cs->rating = 0;
		return;
	}

	if (cs->mark_unstable)
		cs->mark_unstable(cs);

	/* kick clocksource_watchdog_kthread() */
	if (finished_booting)
		schedule_work(&watchdog_work);
}

/**
 * clocksource_mark_unstable - mark clocksource unstable via watchdog
 * @cs:		clocksource to be marked unstable
 *
 * This function is called by the x86 TSC code to mark clocksources as unstable;
 * it defers demotion and re-selection to a kthread.
 */
void clocksource_mark_unstable(struct clocksource *cs)
{
	unsigned long flags;

	spin_lock_irqsave(&watchdog_lock, flags);
	if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
		if (!list_empty(&cs->list) && list_empty(&cs->wd_list))
			list_add(&cs->wd_list, &watchdog_list);
		__clocksource_unstable(cs);
	}
	spin_unlock_irqrestore(&watchdog_lock, flags);
}

ulong max_cswd_read_retries = 2;
module_param(max_cswd_read_retries, ulong, 0644);
EXPORT_SYMBOL_GPL(max_cswd_read_retries);
static int verify_n_cpus = 8;
module_param(verify_n_cpus, int, 0644);

enum wd_read_status {
	WD_READ_SUCCESS,
	WD_READ_UNSTABLE,
	WD_READ_SKIP
};

static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
{
	unsigned int nretries;
	u64 wd_end, wd_end2, wd_delta;
	int64_t wd_delay, wd_seq_delay;

	for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) {
		local_irq_disable();
		*wdnow = watchdog->read(watchdog);
		*csnow = cs->read(cs);
		wd_end = watchdog->read(watchdog);
		wd_end2 = watchdog->read(watchdog);
		local_irq_enable();

		wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask);
		wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult,
					      watchdog->shift);
		if (wd_delay <= WATCHDOG_MAX_SKEW) {
			if (nretries > 1 || nretries >= max_cswd_read_retries) {
				pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
					smp_processor_id(), watchdog->name, nretries);
			}
			return WD_READ_SUCCESS;
		}

		/*
		 * Now compute delay in consecutive watchdog read to see if
		 * there is too much external interferences that cause
		 * significant delay in reading both clocksource and watchdog.
		 *
		 * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2,
		 * report system busy, reinit the watchdog and skip the current
		 * watchdog test.
		 */
		wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask);
		wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift);
		if (wd_seq_delay > WATCHDOG_MAX_SKEW/2)
			goto skip_test;
	}

	pr_warn("timekeeping watchdog on CPU%d: %s read-back delay of %lldns, attempt %d, marking unstable\n",
		smp_processor_id(), watchdog->name, wd_delay, nretries);
	return WD_READ_UNSTABLE;

skip_test:
	pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
		smp_processor_id(), watchdog->name, wd_seq_delay);
	pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
		cs->name, wd_delay);
	return WD_READ_SKIP;
}

static u64 csnow_mid;
static cpumask_t cpus_ahead;
static cpumask_t cpus_behind;
static cpumask_t cpus_chosen;

static void clocksource_verify_choose_cpus(void)
{
	int cpu, i, n = verify_n_cpus;

	if (n < 0) {
		/* Check all of the CPUs. */
		cpumask_copy(&cpus_chosen, cpu_online_mask);
		cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
		return;
	}

	/* If no checking desired, or no other CPU to check, leave. */
	cpumask_clear(&cpus_chosen);
	if (n == 0 || num_online_cpus() <= 1)
		return;

	/* Make sure to select at least one CPU other than the current CPU. */
	cpu = cpumask_first(cpu_online_mask);
	if (cpu == smp_processor_id())
		cpu = cpumask_next(cpu, cpu_online_mask);
	if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
		return;
	cpumask_set_cpu(cpu, &cpus_chosen);

	/* Force a sane value for the boot parameter. */
	if (n > nr_cpu_ids)
		n = nr_cpu_ids;

	/*
	 * Randomly select the specified number of CPUs.  If the same
	 * CPU is selected multiple times, that CPU is checked only once,
	 * and no replacement CPU is selected.  This gracefully handles
	 * situations where verify_n_cpus is greater than the number of
	 * CPUs that are currently online.
	 */
	for (i = 1; i < n; i++) {
		cpu = prandom_u32() % nr_cpu_ids;
		cpu = cpumask_next(cpu - 1, cpu_online_mask);
		if (cpu >= nr_cpu_ids)
			cpu = cpumask_first(cpu_online_mask);
		if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
			cpumask_set_cpu(cpu, &cpus_chosen);
	}

	/* Don't verify ourselves. */
	cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
}

static void clocksource_verify_one_cpu(void *csin)
{
	struct clocksource *cs = (struct clocksource *)csin;

	csnow_mid = cs->read(cs);
}

void clocksource_verify_percpu(struct clocksource *cs)
{
	int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
	u64 csnow_begin, csnow_end;
	int cpu, testcpu;
	s64 delta;

	if (verify_n_cpus == 0)
		return;
	cpumask_clear(&cpus_ahead);
	cpumask_clear(&cpus_behind);
	cpus_read_lock();
	preempt_disable();
	clocksource_verify_choose_cpus();
	if (cpumask_weight(&cpus_chosen) == 0) {
		preempt_enable();
		cpus_read_unlock();
		pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
		return;
	}
	testcpu = smp_processor_id();
	pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
	for_each_cpu(cpu, &cpus_chosen) {
		if (cpu == testcpu)
			continue;
		csnow_begin = cs->read(cs);
		smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
		csnow_end = cs->read(cs);
		delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
		if (delta < 0)
			cpumask_set_cpu(cpu, &cpus_behind);
		delta = (csnow_end - csnow_mid) & cs->mask;
		if (delta < 0)
			cpumask_set_cpu(cpu, &cpus_ahead);
		delta = clocksource_delta(csnow_end, csnow_begin, cs->mask);
		cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
		if (cs_nsec > cs_nsec_max)
			cs_nsec_max = cs_nsec;
		if (cs_nsec < cs_nsec_min)
			cs_nsec_min = cs_nsec;
	}
	preempt_enable();
	cpus_read_unlock();
	if (!cpumask_empty(&cpus_ahead))
		pr_warn("        CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
			cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
	if (!cpumask_empty(&cpus_behind))
		pr_warn("        CPUs %*pbl behind CPU %d for clocksource %s.\n",
			cpumask_pr_args(&cpus_behind), testcpu, cs->name);
	if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
		pr_warn("        CPU %d check durations %lldns - %lldns for clocksource %s.\n",
			testcpu, cs_nsec_min, cs_nsec_max, cs->name);
}
EXPORT_SYMBOL_GPL(clocksource_verify_percpu);

static void clocksource_watchdog(struct timer_list *unused)
{
	u64 csnow, wdnow, cslast, wdlast, delta;
	int next_cpu, reset_pending;
	int64_t wd_nsec, cs_nsec;
	struct clocksource *cs;
	enum wd_read_status read_ret;
	u32 md;

	spin_lock(&watchdog_lock);
	if (!watchdog_running)
		goto out;

	reset_pending = atomic_read(&watchdog_reset_pending);

	list_for_each_entry(cs, &watchdog_list, wd_list) {

		/* Clocksource already marked unstable? */
		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
			if (finished_booting)
				schedule_work(&watchdog_work);
			continue;
		}

		read_ret = cs_watchdog_read(cs, &csnow, &wdnow);

		if (read_ret != WD_READ_SUCCESS) {
			if (read_ret == WD_READ_UNSTABLE)
				/* Clock readout unreliable, so give it up. */
				__clocksource_unstable(cs);
			continue;
		}

		/* Clocksource initialized ? */
		if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
		    atomic_read(&watchdog_reset_pending)) {
			cs->flags |= CLOCK_SOURCE_WATCHDOG;
			cs->wd_last = wdnow;
			cs->cs_last = csnow;
			continue;
		}

		delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
		wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
					     watchdog->shift);

		delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
		cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
		wdlast = cs->wd_last; /* save these in case we print them */
		cslast = cs->cs_last;
		cs->cs_last = csnow;
		cs->wd_last = wdnow;

		if (atomic_read(&watchdog_reset_pending))
			continue;

		/* Check the deviation from the watchdog clocksource. */
		md = cs->uncertainty_margin + watchdog->uncertainty_margin;
		if (abs(cs_nsec - wd_nsec) > md) {
			pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
				smp_processor_id(), cs->name);
			pr_warn("                      '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
				watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
			pr_warn("                      '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
				cs->name, cs_nsec, csnow, cslast, cs->mask);
			if (curr_clocksource == cs)
				pr_warn("                      '%s' is current clocksource.\n", cs->name);
			else if (curr_clocksource)
				pr_warn("                      '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
			else
				pr_warn("                      No current clocksource.\n");
			__clocksource_unstable(cs);
			continue;
		}

		if (cs == curr_clocksource && cs->tick_stable)
			cs->tick_stable(cs);

		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
		    (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
		    (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
			/* Mark it valid for high-res. */
			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;

			/*
			 * clocksource_done_booting() will sort it if
			 * finished_booting is not set yet.
			 */
			if (!finished_booting)
				continue;

			/*
			 * If this is not the current clocksource let
			 * the watchdog thread reselect it. Due to the
			 * change to high res this clocksource might
			 * be preferred now. If it is the current
			 * clocksource let the tick code know about
			 * that change.
			 */
			if (cs != curr_clocksource) {
				cs->flags |= CLOCK_SOURCE_RESELECT;
				schedule_work(&watchdog_work);
			} else {
				tick_clock_notify();
			}
		}
	}

	/*
	 * We only clear the watchdog_reset_pending, when we did a
	 * full cycle through all clocksources.
	 */
	if (reset_pending)
		atomic_dec(&watchdog_reset_pending);

	/*
	 * Cycle through CPUs to check if the CPUs stay synchronized
	 * to each other.
	 */
	next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
	if (next_cpu >= nr_cpu_ids)
		next_cpu = cpumask_first(cpu_online_mask);

	/*
	 * Arm timer if not already pending: could race with concurrent
	 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
	 */
	if (!timer_pending(&watchdog_timer)) {
		watchdog_timer.expires += WATCHDOG_INTERVAL;
		add_timer_on(&watchdog_timer, next_cpu);
	}
out:
	spin_unlock(&watchdog_lock);
}

static inline void clocksource_start_watchdog(void)
{
	if (watchdog_running || !watchdog || list_empty(&watchdog_list))
		return;
	timer_setup(&watchdog_timer, clocksource_watchdog, 0);
	watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
	add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
	watchdog_running = 1;
}

static inline void clocksource_stop_watchdog(void)
{
	if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
		return;
	del_timer(&watchdog_timer);
	watchdog_running = 0;
}

static inline void clocksource_reset_watchdog(void)
{
	struct clocksource *cs;

	list_for_each_entry(cs, &watchdog_list, wd_list)
		cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
}

static void clocksource_resume_watchdog(void)
{
	atomic_inc(&watchdog_reset_pending);
}

static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
	INIT_LIST_HEAD(&cs->wd_list);

	if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
		/* cs is a clocksource to be watched. */
		list_add(&cs->wd_list, &watchdog_list);
		cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
	} else {
		/* cs is a watchdog. */
		if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
	}
}

static void clocksource_select_watchdog(bool fallback)
{
	struct clocksource *cs, *old_wd;
	unsigned long flags;

	spin_lock_irqsave(&watchdog_lock, flags);
	/* save current watchdog */
	old_wd = watchdog;
	if (fallback)
		watchdog = NULL;

	list_for_each_entry(cs, &clocksource_list, list) {
		/* cs is a clocksource to be watched. */
		if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
			continue;

		/* Skip current if we were requested for a fallback. */
		if (fallback && cs == old_wd)
			continue;

		/* Pick the best watchdog. */
		if (!watchdog || cs->rating > watchdog->rating)
			watchdog = cs;
	}
	/* If we failed to find a fallback restore the old one. */
	if (!watchdog)
		watchdog = old_wd;

	/* If we changed the watchdog we need to reset cycles. */
	if (watchdog != old_wd)
		clocksource_reset_watchdog();

	/* Check if the watchdog timer needs to be started. */
	clocksource_start_watchdog();
	spin_unlock_irqrestore(&watchdog_lock, flags);
}

static void clocksource_dequeue_watchdog(struct clocksource *cs)
{
	if (cs != watchdog) {
		if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
			/* cs is a watched clocksource. */
			list_del_init(&cs->wd_list);
			/* Check if the watchdog timer needs to be stopped. */
			clocksource_stop_watchdog();
		}
	}
}

static int __clocksource_watchdog_kthread(void)
{
	struct clocksource *cs, *tmp;
	unsigned long flags;
	int select = 0;

	/* Do any required per-CPU skew verification. */
	if (curr_clocksource &&
	    curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
	    curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
		clocksource_verify_percpu(curr_clocksource);

	spin_lock_irqsave(&watchdog_lock, flags);
	list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
			list_del_init(&cs->wd_list);
			__clocksource_change_rating(cs, 0);
			select = 1;
		}
		if (cs->flags & CLOCK_SOURCE_RESELECT) {
			cs->flags &= ~CLOCK_SOURCE_RESELECT;
			select = 1;
		}
	}
	/* Check if the watchdog timer needs to be stopped. */
	clocksource_stop_watchdog();
	spin_unlock_irqrestore(&watchdog_lock, flags);

	return select;
}

static int clocksource_watchdog_kthread(void *data)
{
	mutex_lock(&clocksource_mutex);
	if (__clocksource_watchdog_kthread())
		clocksource_select();
	mutex_unlock(&clocksource_mutex);
	return 0;
}

static bool clocksource_is_watchdog(struct clocksource *cs)
{
	return cs == watchdog;
}

#else /* CONFIG_CLOCKSOURCE_WATCHDOG */

static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
	if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
		cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
}

static void clocksource_select_watchdog(bool fallback) { }
static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
static inline void clocksource_resume_watchdog(void) { }
static inline int __clocksource_watchdog_kthread(void) { return 0; }
static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
void clocksource_mark_unstable(struct clocksource *cs) { }

static inline void clocksource_watchdog_lock(unsigned long *flags) { }
static inline void clocksource_watchdog_unlock(unsigned long *flags) { }

#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */

static bool clocksource_is_suspend(struct clocksource *cs)
{
	return cs == suspend_clocksource;
}

static void __clocksource_suspend_select(struct clocksource *cs)
{
	/*
	 * Skip the clocksource which will be stopped in suspend state.
	 */
	if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
		return;

	/*
	 * The nonstop clocksource can be selected as the suspend clocksource to
	 * calculate the suspend time, so it should not supply suspend/resume
	 * interfaces to suspend the nonstop clocksource when system suspends.
	 */
	if (cs->suspend || cs->resume) {
		pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
			cs->name);
	}

	/* Pick the best rating. */
	if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
		suspend_clocksource = cs;
}

/**
 * clocksource_suspend_select - Select the best clocksource for suspend timing
 * @fallback:	if select a fallback clocksource
 */
static void clocksource_suspend_select(bool fallback)
{
	struct clocksource *cs, *old_suspend;

	old_suspend = suspend_clocksource;
	if (fallback)
		suspend_clocksource = NULL;

	list_for_each_entry(cs, &clocksource_list, list) {
		/* Skip current if we were requested for a fallback. */
		if (fallback && cs == old_suspend)
			continue;

		__clocksource_suspend_select(cs);
	}
}

/**
 * clocksource_start_suspend_timing - Start measuring the suspend timing
 * @cs:			current clocksource from timekeeping
 * @start_cycles:	current cycles from timekeeping
 *
 * This function will save the start cycle values of suspend timer to calculate
 * the suspend time when resuming system.
 *
 * This function is called late in the suspend process from timekeeping_suspend(),
 * that means processes are frozen, non-boot cpus and interrupts are disabled
 * now. It is therefore possible to start the suspend timer without taking the
 * clocksource mutex.
 */
void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
{
	if (!suspend_clocksource)
		return;

	/*
	 * If current clocksource is the suspend timer, we should use the
	 * tkr_mono.cycle_last value as suspend_start to avoid same reading
	 * from suspend timer.
	 */
	if (clocksource_is_suspend(cs)) {
		suspend_start = start_cycles;
		return;
	}

	if (suspend_clocksource->enable &&
	    suspend_clocksource->enable(suspend_clocksource)) {
		pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
		return;
	}

	suspend_start = suspend_clocksource->read(suspend_clocksource);
}

/**
 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
 * @cs:		current clocksource from timekeeping
 * @cycle_now:	current cycles from timekeeping
 *
 * This function will calculate the suspend time from suspend timer.
 *
 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
 *
 * This function is called early in the resume process from timekeeping_resume(),
 * that means there is only one cpu, no processes are running and the interrupts
 * are disabled. It is therefore possible to stop the suspend timer without
 * taking the clocksource mutex.
 */
u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
{
	u64 now, delta, nsec = 0;

	if (!suspend_clocksource)
		return 0;

	/*
	 * If current clocksource is the suspend timer, we should use the
	 * tkr_mono.cycle_last value from timekeeping as current cycle to
	 * avoid same reading from suspend timer.
	 */
	if (clocksource_is_suspend(cs))
		now = cycle_now;
	else
		now = suspend_clocksource->read(suspend_clocksource);

	if (now > suspend_start) {
		delta = clocksource_delta(now, suspend_start,
					  suspend_clocksource->mask);
		nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
				       suspend_clocksource->shift);
	}

	/*
	 * Disable the suspend timer to save power if current clocksource is
	 * not the suspend timer.
	 */
	if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
		suspend_clocksource->disable(suspend_clocksource);

	return nsec;
}

/**
 * clocksource_suspend - suspend the clocksource(s)
 */
void clocksource_suspend(void)
{
	struct clocksource *cs;

	list_for_each_entry_reverse(cs, &clocksource_list, list)
		if (cs->suspend)
			cs->suspend(cs);
}

/**
 * clocksource_resume - resume the clocksource(s)
 */
void clocksource_resume(void)
{
	struct clocksource *cs;

	list_for_each_entry(cs, &clocksource_list, list)
		if (cs->resume)
			cs->resume(cs);

	clocksource_resume_watchdog();
}

/**
 * clocksource_touch_watchdog - Update watchdog
 *
 * Update the watchdog after exception contexts such as kgdb so as not
 * to incorrectly trip the watchdog. This might fail when the kernel
 * was stopped in code which holds watchdog_lock.
 */
void clocksource_touch_watchdog(void)
{
	clocksource_resume_watchdog();
}

/**
 * clocksource_max_adjustment- Returns max adjustment amount
 * @cs:         Pointer to clocksource
 *
 */
static u32 clocksource_max_adjustment(struct clocksource *cs)
{
	u64 ret;
	/*
	 * We won't try to correct for more than 11% adjustments (110,000 ppm),
	 */
	ret = (u64)cs->mult * 11;
	do_div(ret,100);
	return (u32)ret;
}

/**
 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
 * @mult:	cycle to nanosecond multiplier
 * @shift:	cycle to nanosecond divisor (power of two)
 * @maxadj:	maximum adjustment value to mult (~11%)
 * @mask:	bitmask for two's complement subtraction of non 64 bit counters
 * @max_cyc:	maximum cycle value before potential overflow (does not include
 *		any safety margin)
 *
 * NOTE: This function includes a safety margin of 50%, in other words, we
 * return half the number of nanoseconds the hardware counter can technically
 * cover. This is done so that we can potentially detect problems caused by
 * delayed timers or bad hardware, which might result in time intervals that
 * are larger than what the math used can handle without overflows.
 */
u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
{
	u64 max_nsecs, max_cycles;

	/*
	 * Calculate the maximum number of cycles that we can pass to the
	 * cyc2ns() function without overflowing a 64-bit result.
	 */
	max_cycles = ULLONG_MAX;
	do_div(max_cycles, mult+maxadj);

	/*
	 * The actual maximum number of cycles we can defer the clocksource is
	 * determined by the minimum of max_cycles and mask.
	 * Note: Here we subtract the maxadj to make sure we don't sleep for
	 * too long if there's a large negative adjustment.
	 */
	max_cycles = min(max_cycles, mask);
	max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);

	/* return the max_cycles value as well if requested */
	if (max_cyc)
		*max_cyc = max_cycles;

	/* Return 50% of the actual maximum, so we can detect bad values */
	max_nsecs >>= 1;

	return max_nsecs;
}

/**
 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
 * @cs:         Pointer to clocksource to be updated
 *
 */
static inline void clocksource_update_max_deferment(struct clocksource *cs)
{
	cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
						cs->maxadj, cs->mask,
						&cs->max_cycles);
}

static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
{
	struct clocksource *cs;

	if (!finished_booting || list_empty(&clocksource_list))
		return NULL;

	/*
	 * We pick the clocksource with the highest rating. If oneshot
	 * mode is active, we pick the highres valid clocksource with
	 * the best rating.
	 */
	list_for_each_entry(cs, &clocksource_list, list) {
		if (skipcur && cs == curr_clocksource)
			continue;
		if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
			continue;
		return cs;
	}
	return NULL;
}

static void __clocksource_select(bool skipcur)
{
	bool oneshot = tick_oneshot_mode_active();
	struct clocksource *best, *cs;

	/* Find the best suitable clocksource */
	best = clocksource_find_best(oneshot, skipcur);
	if (!best)
		return;

	if (!strlen(override_name))
		goto found;

	/* Check for the override clocksource. */
	list_for_each_entry(cs, &clocksource_list, list) {
		if (skipcur && cs == curr_clocksource)
			continue;
		if (strcmp(cs->name, override_name) != 0)
			continue;
		/*
		 * Check to make sure we don't switch to a non-highres
		 * capable clocksource if the tick code is in oneshot
		 * mode (highres or nohz)
		 */
		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
			/* Override clocksource cannot be used. */
			if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
				pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
					cs->name);
				override_name[0] = 0;
			} else {
				/*
				 * The override cannot be currently verified.
				 * Deferring to let the watchdog check.
				 */
				pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
					cs->name);
			}
		} else
			/* Override clocksource can be used. */
			best = cs;
		break;
	}

found:
	if (curr_clocksource != best && !timekeeping_notify(best)) {
		pr_info("Switched to clocksource %s\n", best->name);
		curr_clocksource = best;
	}
}

/**
 * clocksource_select - Select the best clocksource available
 *
 * Private function. Must hold clocksource_mutex when called.
 *
 * Select the clocksource with the best rating, or the clocksource,
 * which is selected by userspace override.
 */
static void clocksource_select(void)
{
	__clocksource_select(false);
}

static void clocksource_select_fallback(void)
{
	__clocksource_select(true);
}

/*
 * clocksource_done_booting - Called near the end of core bootup
 *
 * Hack to avoid lots of clocksource churn at boot time.
 * We use fs_initcall because we want this to start before
 * device_initcall but after subsys_initcall.
 */
static int __init clocksource_done_booting(void)
{
	mutex_lock(&clocksource_mutex);
	curr_clocksource = clocksource_default_clock();
	finished_booting = 1;
	/*
	 * Run the watchdog first to eliminate unstable clock sources
	 */
	__clocksource_watchdog_kthread();
	clocksource_select();
	mutex_unlock(&clocksource_mutex);
	return 0;
}
fs_initcall(clocksource_done_booting);

/*
 * Enqueue the clocksource sorted by rating
 */
static void clocksource_enqueue(struct clocksource *cs)
{
	struct list_head *entry = &clocksource_list;
	struct clocksource *tmp;

	list_for_each_entry(tmp, &clocksource_list, list) {
		/* Keep track of the place, where to insert */
		if (tmp->rating < cs->rating)
			break;
		entry = &tmp->list;
	}
	list_add(&cs->list, entry);
}

/**
 * __clocksource_update_freq_scale - Used update clocksource with new freq
 * @cs:		clocksource to be registered
 * @scale:	Scale factor multiplied against freq to get clocksource hz
 * @freq:	clocksource frequency (cycles per second) divided by scale
 *
 * This should only be called from the clocksource->enable() method.
 *
 * This *SHOULD NOT* be called directly! Please use the
 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
 * functions.
 */
void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
{
	u64 sec;

	/*
	 * Default clocksources are *special* and self-define their mult/shift.
	 * But, you're not special, so you should specify a freq value.
	 */
	if (freq) {
		/*
		 * Calc the maximum number of seconds which we can run before
		 * wrapping around. For clocksources which have a mask > 32-bit
		 * we need to limit the max sleep time to have a good
		 * conversion precision. 10 minutes is still a reasonable
		 * amount. That results in a shift value of 24 for a
		 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
		 * ~ 0.06ppm granularity for NTP.
		 */
		sec = cs->mask;
		do_div(sec, freq);
		do_div(sec, scale);
		if (!sec)
			sec = 1;
		else if (sec > 600 && cs->mask > UINT_MAX)
			sec = 600;

		clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
				       NSEC_PER_SEC / scale, sec * scale);
	}

	/*
	 * If the uncertainty margin is not specified, calculate it.
	 * If both scale and freq are non-zero, calculate the clock
	 * period, but bound below at 2*WATCHDOG_MAX_SKEW.  However,
	 * if either of scale or freq is zero, be very conservative and
	 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the
	 * uncertainty margin.  Allow stupidly small uncertainty margins
	 * to be specified by the caller for testing purposes, but warn
	 * to discourage production use of this capability.
	 */
	if (scale && freq && !cs->uncertainty_margin) {
		cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
		if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
			cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
	} else if (!cs->uncertainty_margin) {
		cs->uncertainty_margin = WATCHDOG_THRESHOLD;
	}
	WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);

	/*
	 * Ensure clocksources that have large 'mult' values don't overflow
	 * when adjusted.
	 */
	cs->maxadj = clocksource_max_adjustment(cs);
	while (freq && ((cs->mult + cs->maxadj < cs->mult)
		|| (cs->mult - cs->maxadj > cs->mult))) {
		cs->mult >>= 1;
		cs->shift--;
		cs->maxadj = clocksource_max_adjustment(cs);
	}

	/*
	 * Only warn for *special* clocksources that self-define
	 * their mult/shift values and don't specify a freq.
	 */
	WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
		"timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
		cs->name);

	clocksource_update_max_deferment(cs);

	pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
		cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
}
EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);

/**
 * __clocksource_register_scale - Used to install new clocksources
 * @cs:		clocksource to be registered
 * @scale:	Scale factor multiplied against freq to get clocksource hz
 * @freq:	clocksource frequency (cycles per second) divided by scale
 *
 * Returns -EBUSY if registration fails, zero otherwise.
 *
 * This *SHOULD NOT* be called directly! Please use the
 * clocksource_register_hz() or clocksource_register_khz helper functions.
 */
int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
{
	unsigned long flags;

	clocksource_arch_init(cs);

	if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
		cs->id = CSID_GENERIC;
	if (cs->vdso_clock_mode < 0 ||
	    cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
		pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
			cs->name, cs->vdso_clock_mode);
		cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
	}

	/* Initialize mult/shift and max_idle_ns */
	__clocksource_update_freq_scale(cs, scale, freq);

	/* Add clocksource to the clocksource list */
	mutex_lock(&clocksource_mutex);

	clocksource_watchdog_lock(&flags);
	clocksource_enqueue(cs);
	clocksource_enqueue_watchdog(cs);
	clocksource_watchdog_unlock(&flags);

	clocksource_select();
	clocksource_select_watchdog(false);
	__clocksource_suspend_select(cs);
	mutex_unlock(&clocksource_mutex);
	return 0;
}
EXPORT_SYMBOL_GPL(__clocksource_register_scale);

static void __clocksource_change_rating(struct clocksource *cs, int rating)
{
	list_del(&cs->list);
	cs->rating = rating;
	clocksource_enqueue(cs);
}

/**
 * clocksource_change_rating - Change the rating of a registered clocksource
 * @cs:		clocksource to be changed
 * @rating:	new rating
 */
void clocksource_change_rating(struct clocksource *cs, int rating)
{
	unsigned long flags;

	mutex_lock(&clocksource_mutex);
	clocksource_watchdog_lock(&flags);
	__clocksource_change_rating(cs, rating);
	clocksource_watchdog_unlock(&flags);

	clocksource_select();
	clocksource_select_watchdog(false);
	clocksource_suspend_select(false);
	mutex_unlock(&clocksource_mutex);
}
EXPORT_SYMBOL(clocksource_change_rating);

/*
 * Unbind clocksource @cs. Called with clocksource_mutex held
 */
static int clocksource_unbind(struct clocksource *cs)
{
	unsigned long flags;

	if (clocksource_is_watchdog(cs)) {
		/* Select and try to install a replacement watchdog. */
		clocksource_select_watchdog(true);
		if (clocksource_is_watchdog(cs))
			return -EBUSY;
	}

	if (cs == curr_clocksource) {
		/* Select and try to install a replacement clock source */
		clocksource_select_fallback();
		if (curr_clocksource == cs)
			return -EBUSY;
	}

	if (clocksource_is_suspend(cs)) {
		/*
		 * Select and try to install a replacement suspend clocksource.
		 * If no replacement suspend clocksource, we will just let the
		 * clocksource go and have no suspend clocksource.
		 */
		clocksource_suspend_select(true);
	}

	clocksource_watchdog_lock(&flags);
	clocksource_dequeue_watchdog(cs);
	list_del_init(&cs->list);
	clocksource_watchdog_unlock(&flags);

	return 0;
}

/**
 * clocksource_unregister - remove a registered clocksource
 * @cs:	clocksource to be unregistered
 */
int clocksource_unregister(struct clocksource *cs)
{
	int ret = 0;

	mutex_lock(&clocksource_mutex);
	if (!list_empty(&cs->list))
		ret = clocksource_unbind(cs);
	mutex_unlock(&clocksource_mutex);
	return ret;
}
EXPORT_SYMBOL(clocksource_unregister);

#ifdef CONFIG_SYSFS
/**
 * current_clocksource_show - sysfs interface for current clocksource
 * @dev:	unused
 * @attr:	unused
 * @buf:	char buffer to be filled with clocksource list
 *
 * Provides sysfs interface for listing current clocksource.
 */
static ssize_t current_clocksource_show(struct device *dev,
					struct device_attribute *attr,
					char *buf)
{
	ssize_t count = 0;

	mutex_lock(&clocksource_mutex);
	count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
	mutex_unlock(&clocksource_mutex);

	return count;
}

ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
{
	size_t ret = cnt;

	/* strings from sysfs write are not 0 terminated! */
	if (!cnt || cnt >= CS_NAME_LEN)
		return -EINVAL;

	/* strip of \n: */
	if (buf[cnt-1] == '\n')
		cnt--;
	if (cnt > 0)
		memcpy(dst, buf, cnt);
	dst[cnt] = 0;
	return ret;
}

/**
 * current_clocksource_store - interface for manually overriding clocksource
 * @dev:	unused
 * @attr:	unused
 * @buf:	name of override clocksource
 * @count:	length of buffer
 *
 * Takes input from sysfs interface for manually overriding the default
 * clocksource selection.
 */
static ssize_t current_clocksource_store(struct device *dev,
					 struct device_attribute *attr,
					 const char *buf, size_t count)
{
	ssize_t ret;

	mutex_lock(&clocksource_mutex);

	ret = sysfs_get_uname(buf, override_name, count);
	if (ret >= 0)
		clocksource_select();

	mutex_unlock(&clocksource_mutex);

	return ret;
}
static DEVICE_ATTR_RW(current_clocksource);

/**
 * unbind_clocksource_store - interface for manually unbinding clocksource
 * @dev:	unused
 * @attr:	unused
 * @buf:	unused
 * @count:	length of buffer
 *
 * Takes input from sysfs interface for manually unbinding a clocksource.
 */
static ssize_t unbind_clocksource_store(struct device *dev,
					struct device_attribute *attr,
					const char *buf, size_t count)
{
	struct clocksource *cs;
	char name[CS_NAME_LEN];
	ssize_t ret;

	ret = sysfs_get_uname(buf, name, count);
	if (ret < 0)
		return ret;

	ret = -ENODEV;
	mutex_lock(&clocksource_mutex);
	list_for_each_entry(cs, &clocksource_list, list) {
		if (strcmp(cs->name, name))
			continue;
		ret = clocksource_unbind(cs);
		break;
	}
	mutex_unlock(&clocksource_mutex);

	return ret ? ret : count;
}
static DEVICE_ATTR_WO(unbind_clocksource);

/**
 * available_clocksource_show - sysfs interface for listing clocksource
 * @dev:	unused
 * @attr:	unused
 * @buf:	char buffer to be filled with clocksource list
 *
 * Provides sysfs interface for listing registered clocksources
 */
static ssize_t available_clocksource_show(struct device *dev,
					  struct device_attribute *attr,
					  char *buf)
{
	struct clocksource *src;
	ssize_t count = 0;

	mutex_lock(&clocksource_mutex);
	list_for_each_entry(src, &clocksource_list, list) {
		/*
		 * Don't show non-HRES clocksource if the tick code is
		 * in one shot mode (highres=on or nohz=on)
		 */
		if (!tick_oneshot_mode_active() ||
		    (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
			count += snprintf(buf + count,
				  max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
				  "%s ", src->name);
	}
	mutex_unlock(&clocksource_mutex);

	count += snprintf(buf + count,
			  max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");

	return count;
}
static DEVICE_ATTR_RO(available_clocksource);

static struct attribute *clocksource_attrs[] = {
	&dev_attr_current_clocksource.attr,
	&dev_attr_unbind_clocksource.attr,
	&dev_attr_available_clocksource.attr,
	NULL
};
ATTRIBUTE_GROUPS(clocksource);

static struct bus_type clocksource_subsys = {
	.name = "clocksource",
	.dev_name = "clocksource",
};

static struct device device_clocksource = {
	.id	= 0,
	.bus	= &clocksource_subsys,
	.groups	= clocksource_groups,
};

static int __init init_clocksource_sysfs(void)
{
	int error = subsys_system_register(&clocksource_subsys, NULL);

	if (!error)
		error = device_register(&device_clocksource);

	return error;
}

device_initcall(init_clocksource_sysfs);
#endif /* CONFIG_SYSFS */

/**
 * boot_override_clocksource - boot clock override
 * @str:	override name
 *
 * Takes a clocksource= boot argument and uses it
 * as the clocksource override name.
 */
static int __init boot_override_clocksource(char* str)
{
	mutex_lock(&clocksource_mutex);
	if (str)
		strlcpy(override_name, str, sizeof(override_name));
	mutex_unlock(&clocksource_mutex);
	return 1;
}

__setup("clocksource=", boot_override_clocksource);

/**
 * boot_override_clock - Compatibility layer for deprecated boot option
 * @str:	override name
 *
 * DEPRECATED! Takes a clock= boot argument and uses it
 * as the clocksource override name
 */
static int __init boot_override_clock(char* str)
{
	if (!strcmp(str, "pmtmr")) {
		pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
		return boot_override_clocksource("acpi_pm");
	}
	pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
	return boot_override_clocksource(str);
}

__setup("clock=", boot_override_clock);