1 // SPDX-License-Identifier: GPL-2.0+
2 /*
3  * This file contains the functions which manage clocksource drivers.
4  *
5  * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
6  */
7 
8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9 
10 #include <linux/device.h>
11 #include <linux/clocksource.h>
12 #include <linux/init.h>
13 #include <linux/module.h>
14 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
15 #include <linux/tick.h>
16 #include <linux/kthread.h>
17 #include <linux/prandom.h>
18 #include <linux/cpu.h>
19 
20 #include "tick-internal.h"
21 #include "timekeeping_internal.h"
22 
23 /**
24  * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
25  * @mult:	pointer to mult variable
26  * @shift:	pointer to shift variable
27  * @from:	frequency to convert from
28  * @to:		frequency to convert to
29  * @maxsec:	guaranteed runtime conversion range in seconds
30  *
31  * The function evaluates the shift/mult pair for the scaled math
32  * operations of clocksources and clockevents.
33  *
34  * @to and @from are frequency values in HZ. For clock sources @to is
35  * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
36  * event @to is the counter frequency and @from is NSEC_PER_SEC.
37  *
38  * The @maxsec conversion range argument controls the time frame in
39  * seconds which must be covered by the runtime conversion with the
40  * calculated mult and shift factors. This guarantees that no 64bit
41  * overflow happens when the input value of the conversion is
42  * multiplied with the calculated mult factor. Larger ranges may
43  * reduce the conversion accuracy by choosing smaller mult and shift
44  * factors.
45  */
46 void
clocks_calc_mult_shift(u32 * mult,u32 * shift,u32 from,u32 to,u32 maxsec)47 clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
48 {
49 	u64 tmp;
50 	u32 sft, sftacc= 32;
51 
52 	/*
53 	 * Calculate the shift factor which is limiting the conversion
54 	 * range:
55 	 */
56 	tmp = ((u64)maxsec * from) >> 32;
57 	while (tmp) {
58 		tmp >>=1;
59 		sftacc--;
60 	}
61 
62 	/*
63 	 * Find the conversion shift/mult pair which has the best
64 	 * accuracy and fits the maxsec conversion range:
65 	 */
66 	for (sft = 32; sft > 0; sft--) {
67 		tmp = (u64) to << sft;
68 		tmp += from / 2;
69 		do_div(tmp, from);
70 		if ((tmp >> sftacc) == 0)
71 			break;
72 	}
73 	*mult = tmp;
74 	*shift = sft;
75 }
76 EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
77 
78 /*[Clocksource internal variables]---------
79  * curr_clocksource:
80  *	currently selected clocksource.
81  * suspend_clocksource:
82  *	used to calculate the suspend time.
83  * clocksource_list:
84  *	linked list with the registered clocksources
85  * clocksource_mutex:
86  *	protects manipulations to curr_clocksource and the clocksource_list
87  * override_name:
88  *	Name of the user-specified clocksource.
89  */
90 static struct clocksource *curr_clocksource;
91 static struct clocksource *suspend_clocksource;
92 static LIST_HEAD(clocksource_list);
93 static DEFINE_MUTEX(clocksource_mutex);
94 static char override_name[CS_NAME_LEN];
95 static int finished_booting;
96 static u64 suspend_start;
97 
98 /*
99  * Interval: 0.5sec.
100  */
101 #define WATCHDOG_INTERVAL (HZ >> 1)
102 #define WATCHDOG_INTERVAL_MAX_NS ((2 * WATCHDOG_INTERVAL) * (NSEC_PER_SEC / HZ))
103 
104 /*
105  * Threshold: 0.0312s, when doubled: 0.0625s.
106  * Also a default for cs->uncertainty_margin when registering clocks.
107  */
108 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5)
109 
110 /*
111  * Maximum permissible delay between two readouts of the watchdog
112  * clocksource surrounding a read of the clocksource being validated.
113  * This delay could be due to SMIs, NMIs, or to VCPU preemptions.  Used as
114  * a lower bound for cs->uncertainty_margin values when registering clocks.
115  *
116  * The default of 500 parts per million is based on NTP's limits.
117  * If a clocksource is good enough for NTP, it is good enough for us!
118  */
119 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
120 #define MAX_SKEW_USEC	CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
121 #else
122 #define MAX_SKEW_USEC	(125 * WATCHDOG_INTERVAL / HZ)
123 #endif
124 
125 #define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
126 
127 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
128 static void clocksource_watchdog_work(struct work_struct *work);
129 static void clocksource_select(void);
130 
131 static LIST_HEAD(watchdog_list);
132 static struct clocksource *watchdog;
133 static struct timer_list watchdog_timer;
134 static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
135 static DEFINE_SPINLOCK(watchdog_lock);
136 static int watchdog_running;
137 static atomic_t watchdog_reset_pending;
138 static int64_t watchdog_max_interval;
139 
clocksource_watchdog_lock(unsigned long * flags)140 static inline void clocksource_watchdog_lock(unsigned long *flags)
141 {
142 	spin_lock_irqsave(&watchdog_lock, *flags);
143 }
144 
clocksource_watchdog_unlock(unsigned long * flags)145 static inline void clocksource_watchdog_unlock(unsigned long *flags)
146 {
147 	spin_unlock_irqrestore(&watchdog_lock, *flags);
148 }
149 
150 static int clocksource_watchdog_kthread(void *data);
151 static void __clocksource_change_rating(struct clocksource *cs, int rating);
152 
clocksource_watchdog_work(struct work_struct * work)153 static void clocksource_watchdog_work(struct work_struct *work)
154 {
155 	/*
156 	 * We cannot directly run clocksource_watchdog_kthread() here, because
157 	 * clocksource_select() calls timekeeping_notify() which uses
158 	 * stop_machine(). One cannot use stop_machine() from a workqueue() due
159 	 * lock inversions wrt CPU hotplug.
160 	 *
161 	 * Also, we only ever run this work once or twice during the lifetime
162 	 * of the kernel, so there is no point in creating a more permanent
163 	 * kthread for this.
164 	 *
165 	 * If kthread_run fails the next watchdog scan over the
166 	 * watchdog_list will find the unstable clock again.
167 	 */
168 	kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
169 }
170 
__clocksource_unstable(struct clocksource * cs)171 static void __clocksource_unstable(struct clocksource *cs)
172 {
173 	cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
174 	cs->flags |= CLOCK_SOURCE_UNSTABLE;
175 
176 	/*
177 	 * If the clocksource is registered clocksource_watchdog_kthread() will
178 	 * re-rate and re-select.
179 	 */
180 	if (list_empty(&cs->list)) {
181 		cs->rating = 0;
182 		return;
183 	}
184 
185 	if (cs->mark_unstable)
186 		cs->mark_unstable(cs);
187 
188 	/* kick clocksource_watchdog_kthread() */
189 	if (finished_booting)
190 		schedule_work(&watchdog_work);
191 }
192 
193 /**
194  * clocksource_mark_unstable - mark clocksource unstable via watchdog
195  * @cs:		clocksource to be marked unstable
196  *
197  * This function is called by the x86 TSC code to mark clocksources as unstable;
198  * it defers demotion and re-selection to a kthread.
199  */
clocksource_mark_unstable(struct clocksource * cs)200 void clocksource_mark_unstable(struct clocksource *cs)
201 {
202 	unsigned long flags;
203 
204 	spin_lock_irqsave(&watchdog_lock, flags);
205 	if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
206 		if (!list_empty(&cs->list) && list_empty(&cs->wd_list))
207 			list_add(&cs->wd_list, &watchdog_list);
208 		__clocksource_unstable(cs);
209 	}
210 	spin_unlock_irqrestore(&watchdog_lock, flags);
211 }
212 
213 ulong max_cswd_read_retries = 2;
214 module_param(max_cswd_read_retries, ulong, 0644);
215 EXPORT_SYMBOL_GPL(max_cswd_read_retries);
216 static int verify_n_cpus = 8;
217 module_param(verify_n_cpus, int, 0644);
218 
219 enum wd_read_status {
220 	WD_READ_SUCCESS,
221 	WD_READ_UNSTABLE,
222 	WD_READ_SKIP
223 };
224 
cs_watchdog_read(struct clocksource * cs,u64 * csnow,u64 * wdnow)225 static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
226 {
227 	unsigned int nretries;
228 	u64 wd_end, wd_end2, wd_delta;
229 	int64_t wd_delay, wd_seq_delay;
230 
231 	for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) {
232 		local_irq_disable();
233 		*wdnow = watchdog->read(watchdog);
234 		*csnow = cs->read(cs);
235 		wd_end = watchdog->read(watchdog);
236 		wd_end2 = watchdog->read(watchdog);
237 		local_irq_enable();
238 
239 		wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask);
240 		wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult,
241 					      watchdog->shift);
242 		if (wd_delay <= WATCHDOG_MAX_SKEW) {
243 			if (nretries > 1 || nretries >= max_cswd_read_retries) {
244 				pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
245 					smp_processor_id(), watchdog->name, nretries);
246 			}
247 			return WD_READ_SUCCESS;
248 		}
249 
250 		/*
251 		 * Now compute delay in consecutive watchdog read to see if
252 		 * there is too much external interferences that cause
253 		 * significant delay in reading both clocksource and watchdog.
254 		 *
255 		 * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2,
256 		 * report system busy, reinit the watchdog and skip the current
257 		 * watchdog test.
258 		 */
259 		wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask);
260 		wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift);
261 		if (wd_seq_delay > WATCHDOG_MAX_SKEW/2)
262 			goto skip_test;
263 	}
264 
265 	pr_warn("timekeeping watchdog on CPU%d: wd-%s-wd excessive read-back delay of %lldns vs. limit of %ldns, wd-wd read-back delay only %lldns, attempt %d, marking %s unstable\n",
266 		smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name);
267 	return WD_READ_UNSTABLE;
268 
269 skip_test:
270 	pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
271 		smp_processor_id(), watchdog->name, wd_seq_delay);
272 	pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
273 		cs->name, wd_delay);
274 	return WD_READ_SKIP;
275 }
276 
277 static u64 csnow_mid;
278 static cpumask_t cpus_ahead;
279 static cpumask_t cpus_behind;
280 static cpumask_t cpus_chosen;
281 
clocksource_verify_choose_cpus(void)282 static void clocksource_verify_choose_cpus(void)
283 {
284 	int cpu, i, n = verify_n_cpus;
285 
286 	if (n < 0) {
287 		/* Check all of the CPUs. */
288 		cpumask_copy(&cpus_chosen, cpu_online_mask);
289 		cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
290 		return;
291 	}
292 
293 	/* If no checking desired, or no other CPU to check, leave. */
294 	cpumask_clear(&cpus_chosen);
295 	if (n == 0 || num_online_cpus() <= 1)
296 		return;
297 
298 	/* Make sure to select at least one CPU other than the current CPU. */
299 	cpu = cpumask_first(cpu_online_mask);
300 	if (cpu == smp_processor_id())
301 		cpu = cpumask_next(cpu, cpu_online_mask);
302 	if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
303 		return;
304 	cpumask_set_cpu(cpu, &cpus_chosen);
305 
306 	/* Force a sane value for the boot parameter. */
307 	if (n > nr_cpu_ids)
308 		n = nr_cpu_ids;
309 
310 	/*
311 	 * Randomly select the specified number of CPUs.  If the same
312 	 * CPU is selected multiple times, that CPU is checked only once,
313 	 * and no replacement CPU is selected.  This gracefully handles
314 	 * situations where verify_n_cpus is greater than the number of
315 	 * CPUs that are currently online.
316 	 */
317 	for (i = 1; i < n; i++) {
318 		cpu = get_random_u32_below(nr_cpu_ids);
319 		cpu = cpumask_next(cpu - 1, cpu_online_mask);
320 		if (cpu >= nr_cpu_ids)
321 			cpu = cpumask_first(cpu_online_mask);
322 		if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
323 			cpumask_set_cpu(cpu, &cpus_chosen);
324 	}
325 
326 	/* Don't verify ourselves. */
327 	cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
328 }
329 
clocksource_verify_one_cpu(void * csin)330 static void clocksource_verify_one_cpu(void *csin)
331 {
332 	struct clocksource *cs = (struct clocksource *)csin;
333 
334 	csnow_mid = cs->read(cs);
335 }
336 
clocksource_verify_percpu(struct clocksource * cs)337 void clocksource_verify_percpu(struct clocksource *cs)
338 {
339 	int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
340 	u64 csnow_begin, csnow_end;
341 	int cpu, testcpu;
342 	s64 delta;
343 
344 	if (verify_n_cpus == 0)
345 		return;
346 	cpumask_clear(&cpus_ahead);
347 	cpumask_clear(&cpus_behind);
348 	cpus_read_lock();
349 	preempt_disable();
350 	clocksource_verify_choose_cpus();
351 	if (cpumask_empty(&cpus_chosen)) {
352 		preempt_enable();
353 		cpus_read_unlock();
354 		pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
355 		return;
356 	}
357 	testcpu = smp_processor_id();
358 	pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
359 	for_each_cpu(cpu, &cpus_chosen) {
360 		if (cpu == testcpu)
361 			continue;
362 		csnow_begin = cs->read(cs);
363 		smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
364 		csnow_end = cs->read(cs);
365 		delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
366 		if (delta < 0)
367 			cpumask_set_cpu(cpu, &cpus_behind);
368 		delta = (csnow_end - csnow_mid) & cs->mask;
369 		if (delta < 0)
370 			cpumask_set_cpu(cpu, &cpus_ahead);
371 		delta = clocksource_delta(csnow_end, csnow_begin, cs->mask);
372 		cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
373 		if (cs_nsec > cs_nsec_max)
374 			cs_nsec_max = cs_nsec;
375 		if (cs_nsec < cs_nsec_min)
376 			cs_nsec_min = cs_nsec;
377 	}
378 	preempt_enable();
379 	cpus_read_unlock();
380 	if (!cpumask_empty(&cpus_ahead))
381 		pr_warn("        CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
382 			cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
383 	if (!cpumask_empty(&cpus_behind))
384 		pr_warn("        CPUs %*pbl behind CPU %d for clocksource %s.\n",
385 			cpumask_pr_args(&cpus_behind), testcpu, cs->name);
386 	if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
387 		pr_warn("        CPU %d check durations %lldns - %lldns for clocksource %s.\n",
388 			testcpu, cs_nsec_min, cs_nsec_max, cs->name);
389 }
390 EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
391 
clocksource_reset_watchdog(void)392 static inline void clocksource_reset_watchdog(void)
393 {
394 	struct clocksource *cs;
395 
396 	list_for_each_entry(cs, &watchdog_list, wd_list)
397 		cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
398 }
399 
400 
clocksource_watchdog(struct timer_list * unused)401 static void clocksource_watchdog(struct timer_list *unused)
402 {
403 	u64 csnow, wdnow, cslast, wdlast, delta;
404 	int64_t wd_nsec, cs_nsec, interval;
405 	int next_cpu, reset_pending;
406 	struct clocksource *cs;
407 	enum wd_read_status read_ret;
408 	unsigned long extra_wait = 0;
409 	u32 md;
410 
411 	spin_lock(&watchdog_lock);
412 	if (!watchdog_running)
413 		goto out;
414 
415 	reset_pending = atomic_read(&watchdog_reset_pending);
416 
417 	list_for_each_entry(cs, &watchdog_list, wd_list) {
418 
419 		/* Clocksource already marked unstable? */
420 		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
421 			if (finished_booting)
422 				schedule_work(&watchdog_work);
423 			continue;
424 		}
425 
426 		read_ret = cs_watchdog_read(cs, &csnow, &wdnow);
427 
428 		if (read_ret == WD_READ_UNSTABLE) {
429 			/* Clock readout unreliable, so give it up. */
430 			__clocksource_unstable(cs);
431 			continue;
432 		}
433 
434 		/*
435 		 * When WD_READ_SKIP is returned, it means the system is likely
436 		 * under very heavy load, where the latency of reading
437 		 * watchdog/clocksource is very big, and affect the accuracy of
438 		 * watchdog check. So give system some space and suspend the
439 		 * watchdog check for 5 minutes.
440 		 */
441 		if (read_ret == WD_READ_SKIP) {
442 			/*
443 			 * As the watchdog timer will be suspended, and
444 			 * cs->last could keep unchanged for 5 minutes, reset
445 			 * the counters.
446 			 */
447 			clocksource_reset_watchdog();
448 			extra_wait = HZ * 300;
449 			break;
450 		}
451 
452 		/* Clocksource initialized ? */
453 		if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
454 		    atomic_read(&watchdog_reset_pending)) {
455 			cs->flags |= CLOCK_SOURCE_WATCHDOG;
456 			cs->wd_last = wdnow;
457 			cs->cs_last = csnow;
458 			continue;
459 		}
460 
461 		delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
462 		wd_nsec = clocksource_cyc2ns(delta, watchdog->mult,
463 					     watchdog->shift);
464 
465 		delta = clocksource_delta(csnow, cs->cs_last, cs->mask);
466 		cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift);
467 		wdlast = cs->wd_last; /* save these in case we print them */
468 		cslast = cs->cs_last;
469 		cs->cs_last = csnow;
470 		cs->wd_last = wdnow;
471 
472 		if (atomic_read(&watchdog_reset_pending))
473 			continue;
474 
475 		/*
476 		 * The processing of timer softirqs can get delayed (usually
477 		 * on account of ksoftirqd not getting to run in a timely
478 		 * manner), which causes the watchdog interval to stretch.
479 		 * Skew detection may fail for longer watchdog intervals
480 		 * on account of fixed margins being used.
481 		 * Some clocksources, e.g. acpi_pm, cannot tolerate
482 		 * watchdog intervals longer than a few seconds.
483 		 */
484 		interval = max(cs_nsec, wd_nsec);
485 		if (unlikely(interval > WATCHDOG_INTERVAL_MAX_NS)) {
486 			if (system_state > SYSTEM_SCHEDULING &&
487 			    interval > 2 * watchdog_max_interval) {
488 				watchdog_max_interval = interval;
489 				pr_warn("Long readout interval, skipping watchdog check: cs_nsec: %lld wd_nsec: %lld\n",
490 					cs_nsec, wd_nsec);
491 			}
492 			watchdog_timer.expires = jiffies;
493 			continue;
494 		}
495 
496 		/* Check the deviation from the watchdog clocksource. */
497 		md = cs->uncertainty_margin + watchdog->uncertainty_margin;
498 		if (abs(cs_nsec - wd_nsec) > md) {
499 			s64 cs_wd_msec;
500 			s64 wd_msec;
501 			u32 wd_rem;
502 
503 			pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
504 				smp_processor_id(), cs->name);
505 			pr_warn("                      '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
506 				watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
507 			pr_warn("                      '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
508 				cs->name, cs_nsec, csnow, cslast, cs->mask);
509 			cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem);
510 			wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem);
511 			pr_warn("                      Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n",
512 				cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec);
513 			if (curr_clocksource == cs)
514 				pr_warn("                      '%s' is current clocksource.\n", cs->name);
515 			else if (curr_clocksource)
516 				pr_warn("                      '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
517 			else
518 				pr_warn("                      No current clocksource.\n");
519 			__clocksource_unstable(cs);
520 			continue;
521 		}
522 
523 		if (cs == curr_clocksource && cs->tick_stable)
524 			cs->tick_stable(cs);
525 
526 		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
527 		    (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
528 		    (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
529 			/* Mark it valid for high-res. */
530 			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
531 
532 			/*
533 			 * clocksource_done_booting() will sort it if
534 			 * finished_booting is not set yet.
535 			 */
536 			if (!finished_booting)
537 				continue;
538 
539 			/*
540 			 * If this is not the current clocksource let
541 			 * the watchdog thread reselect it. Due to the
542 			 * change to high res this clocksource might
543 			 * be preferred now. If it is the current
544 			 * clocksource let the tick code know about
545 			 * that change.
546 			 */
547 			if (cs != curr_clocksource) {
548 				cs->flags |= CLOCK_SOURCE_RESELECT;
549 				schedule_work(&watchdog_work);
550 			} else {
551 				tick_clock_notify();
552 			}
553 		}
554 	}
555 
556 	/*
557 	 * We only clear the watchdog_reset_pending, when we did a
558 	 * full cycle through all clocksources.
559 	 */
560 	if (reset_pending)
561 		atomic_dec(&watchdog_reset_pending);
562 
563 	/*
564 	 * Cycle through CPUs to check if the CPUs stay synchronized
565 	 * to each other.
566 	 */
567 	next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
568 	if (next_cpu >= nr_cpu_ids)
569 		next_cpu = cpumask_first(cpu_online_mask);
570 
571 	/*
572 	 * Arm timer if not already pending: could race with concurrent
573 	 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
574 	 */
575 	if (!timer_pending(&watchdog_timer)) {
576 		watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait;
577 		add_timer_on(&watchdog_timer, next_cpu);
578 	}
579 out:
580 	spin_unlock(&watchdog_lock);
581 }
582 
clocksource_start_watchdog(void)583 static inline void clocksource_start_watchdog(void)
584 {
585 	if (watchdog_running || !watchdog || list_empty(&watchdog_list))
586 		return;
587 	timer_setup(&watchdog_timer, clocksource_watchdog, 0);
588 	watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
589 	add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
590 	watchdog_running = 1;
591 }
592 
clocksource_stop_watchdog(void)593 static inline void clocksource_stop_watchdog(void)
594 {
595 	if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
596 		return;
597 	del_timer(&watchdog_timer);
598 	watchdog_running = 0;
599 }
600 
clocksource_resume_watchdog(void)601 static void clocksource_resume_watchdog(void)
602 {
603 	atomic_inc(&watchdog_reset_pending);
604 }
605 
clocksource_enqueue_watchdog(struct clocksource * cs)606 static void clocksource_enqueue_watchdog(struct clocksource *cs)
607 {
608 	INIT_LIST_HEAD(&cs->wd_list);
609 
610 	if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
611 		/* cs is a clocksource to be watched. */
612 		list_add(&cs->wd_list, &watchdog_list);
613 		cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
614 	} else {
615 		/* cs is a watchdog. */
616 		if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
617 			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
618 	}
619 }
620 
clocksource_select_watchdog(bool fallback)621 static void clocksource_select_watchdog(bool fallback)
622 {
623 	struct clocksource *cs, *old_wd;
624 	unsigned long flags;
625 
626 	spin_lock_irqsave(&watchdog_lock, flags);
627 	/* save current watchdog */
628 	old_wd = watchdog;
629 	if (fallback)
630 		watchdog = NULL;
631 
632 	list_for_each_entry(cs, &clocksource_list, list) {
633 		/* cs is a clocksource to be watched. */
634 		if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
635 			continue;
636 
637 		/* Skip current if we were requested for a fallback. */
638 		if (fallback && cs == old_wd)
639 			continue;
640 
641 		/* Pick the best watchdog. */
642 		if (!watchdog || cs->rating > watchdog->rating)
643 			watchdog = cs;
644 	}
645 	/* If we failed to find a fallback restore the old one. */
646 	if (!watchdog)
647 		watchdog = old_wd;
648 
649 	/* If we changed the watchdog we need to reset cycles. */
650 	if (watchdog != old_wd)
651 		clocksource_reset_watchdog();
652 
653 	/* Check if the watchdog timer needs to be started. */
654 	clocksource_start_watchdog();
655 	spin_unlock_irqrestore(&watchdog_lock, flags);
656 }
657 
clocksource_dequeue_watchdog(struct clocksource * cs)658 static void clocksource_dequeue_watchdog(struct clocksource *cs)
659 {
660 	if (cs != watchdog) {
661 		if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
662 			/* cs is a watched clocksource. */
663 			list_del_init(&cs->wd_list);
664 			/* Check if the watchdog timer needs to be stopped. */
665 			clocksource_stop_watchdog();
666 		}
667 	}
668 }
669 
__clocksource_watchdog_kthread(void)670 static int __clocksource_watchdog_kthread(void)
671 {
672 	struct clocksource *cs, *tmp;
673 	unsigned long flags;
674 	int select = 0;
675 
676 	/* Do any required per-CPU skew verification. */
677 	if (curr_clocksource &&
678 	    curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
679 	    curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
680 		clocksource_verify_percpu(curr_clocksource);
681 
682 	spin_lock_irqsave(&watchdog_lock, flags);
683 	list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
684 		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
685 			list_del_init(&cs->wd_list);
686 			__clocksource_change_rating(cs, 0);
687 			select = 1;
688 		}
689 		if (cs->flags & CLOCK_SOURCE_RESELECT) {
690 			cs->flags &= ~CLOCK_SOURCE_RESELECT;
691 			select = 1;
692 		}
693 	}
694 	/* Check if the watchdog timer needs to be stopped. */
695 	clocksource_stop_watchdog();
696 	spin_unlock_irqrestore(&watchdog_lock, flags);
697 
698 	return select;
699 }
700 
clocksource_watchdog_kthread(void * data)701 static int clocksource_watchdog_kthread(void *data)
702 {
703 	mutex_lock(&clocksource_mutex);
704 	if (__clocksource_watchdog_kthread())
705 		clocksource_select();
706 	mutex_unlock(&clocksource_mutex);
707 	return 0;
708 }
709 
clocksource_is_watchdog(struct clocksource * cs)710 static bool clocksource_is_watchdog(struct clocksource *cs)
711 {
712 	return cs == watchdog;
713 }
714 
715 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */
716 
clocksource_enqueue_watchdog(struct clocksource * cs)717 static void clocksource_enqueue_watchdog(struct clocksource *cs)
718 {
719 	if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
720 		cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
721 }
722 
clocksource_select_watchdog(bool fallback)723 static void clocksource_select_watchdog(bool fallback) { }
clocksource_dequeue_watchdog(struct clocksource * cs)724 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
clocksource_resume_watchdog(void)725 static inline void clocksource_resume_watchdog(void) { }
__clocksource_watchdog_kthread(void)726 static inline int __clocksource_watchdog_kthread(void) { return 0; }
clocksource_is_watchdog(struct clocksource * cs)727 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
clocksource_mark_unstable(struct clocksource * cs)728 void clocksource_mark_unstable(struct clocksource *cs) { }
729 
clocksource_watchdog_lock(unsigned long * flags)730 static inline void clocksource_watchdog_lock(unsigned long *flags) { }
clocksource_watchdog_unlock(unsigned long * flags)731 static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
732 
733 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
734 
clocksource_is_suspend(struct clocksource * cs)735 static bool clocksource_is_suspend(struct clocksource *cs)
736 {
737 	return cs == suspend_clocksource;
738 }
739 
__clocksource_suspend_select(struct clocksource * cs)740 static void __clocksource_suspend_select(struct clocksource *cs)
741 {
742 	/*
743 	 * Skip the clocksource which will be stopped in suspend state.
744 	 */
745 	if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
746 		return;
747 
748 	/*
749 	 * The nonstop clocksource can be selected as the suspend clocksource to
750 	 * calculate the suspend time, so it should not supply suspend/resume
751 	 * interfaces to suspend the nonstop clocksource when system suspends.
752 	 */
753 	if (cs->suspend || cs->resume) {
754 		pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
755 			cs->name);
756 	}
757 
758 	/* Pick the best rating. */
759 	if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
760 		suspend_clocksource = cs;
761 }
762 
763 /**
764  * clocksource_suspend_select - Select the best clocksource for suspend timing
765  * @fallback:	if select a fallback clocksource
766  */
clocksource_suspend_select(bool fallback)767 static void clocksource_suspend_select(bool fallback)
768 {
769 	struct clocksource *cs, *old_suspend;
770 
771 	old_suspend = suspend_clocksource;
772 	if (fallback)
773 		suspend_clocksource = NULL;
774 
775 	list_for_each_entry(cs, &clocksource_list, list) {
776 		/* Skip current if we were requested for a fallback. */
777 		if (fallback && cs == old_suspend)
778 			continue;
779 
780 		__clocksource_suspend_select(cs);
781 	}
782 }
783 
784 /**
785  * clocksource_start_suspend_timing - Start measuring the suspend timing
786  * @cs:			current clocksource from timekeeping
787  * @start_cycles:	current cycles from timekeeping
788  *
789  * This function will save the start cycle values of suspend timer to calculate
790  * the suspend time when resuming system.
791  *
792  * This function is called late in the suspend process from timekeeping_suspend(),
793  * that means processes are frozen, non-boot cpus and interrupts are disabled
794  * now. It is therefore possible to start the suspend timer without taking the
795  * clocksource mutex.
796  */
clocksource_start_suspend_timing(struct clocksource * cs,u64 start_cycles)797 void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
798 {
799 	if (!suspend_clocksource)
800 		return;
801 
802 	/*
803 	 * If current clocksource is the suspend timer, we should use the
804 	 * tkr_mono.cycle_last value as suspend_start to avoid same reading
805 	 * from suspend timer.
806 	 */
807 	if (clocksource_is_suspend(cs)) {
808 		suspend_start = start_cycles;
809 		return;
810 	}
811 
812 	if (suspend_clocksource->enable &&
813 	    suspend_clocksource->enable(suspend_clocksource)) {
814 		pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
815 		return;
816 	}
817 
818 	suspend_start = suspend_clocksource->read(suspend_clocksource);
819 }
820 
821 /**
822  * clocksource_stop_suspend_timing - Stop measuring the suspend timing
823  * @cs:		current clocksource from timekeeping
824  * @cycle_now:	current cycles from timekeeping
825  *
826  * This function will calculate the suspend time from suspend timer.
827  *
828  * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
829  *
830  * This function is called early in the resume process from timekeeping_resume(),
831  * that means there is only one cpu, no processes are running and the interrupts
832  * are disabled. It is therefore possible to stop the suspend timer without
833  * taking the clocksource mutex.
834  */
clocksource_stop_suspend_timing(struct clocksource * cs,u64 cycle_now)835 u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
836 {
837 	u64 now, delta, nsec = 0;
838 
839 	if (!suspend_clocksource)
840 		return 0;
841 
842 	/*
843 	 * If current clocksource is the suspend timer, we should use the
844 	 * tkr_mono.cycle_last value from timekeeping as current cycle to
845 	 * avoid same reading from suspend timer.
846 	 */
847 	if (clocksource_is_suspend(cs))
848 		now = cycle_now;
849 	else
850 		now = suspend_clocksource->read(suspend_clocksource);
851 
852 	if (now > suspend_start) {
853 		delta = clocksource_delta(now, suspend_start,
854 					  suspend_clocksource->mask);
855 		nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult,
856 				       suspend_clocksource->shift);
857 	}
858 
859 	/*
860 	 * Disable the suspend timer to save power if current clocksource is
861 	 * not the suspend timer.
862 	 */
863 	if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
864 		suspend_clocksource->disable(suspend_clocksource);
865 
866 	return nsec;
867 }
868 
869 /**
870  * clocksource_suspend - suspend the clocksource(s)
871  */
clocksource_suspend(void)872 void clocksource_suspend(void)
873 {
874 	struct clocksource *cs;
875 
876 	list_for_each_entry_reverse(cs, &clocksource_list, list)
877 		if (cs->suspend)
878 			cs->suspend(cs);
879 }
880 
881 /**
882  * clocksource_resume - resume the clocksource(s)
883  */
clocksource_resume(void)884 void clocksource_resume(void)
885 {
886 	struct clocksource *cs;
887 
888 	list_for_each_entry(cs, &clocksource_list, list)
889 		if (cs->resume)
890 			cs->resume(cs);
891 
892 	clocksource_resume_watchdog();
893 }
894 
895 /**
896  * clocksource_touch_watchdog - Update watchdog
897  *
898  * Update the watchdog after exception contexts such as kgdb so as not
899  * to incorrectly trip the watchdog. This might fail when the kernel
900  * was stopped in code which holds watchdog_lock.
901  */
clocksource_touch_watchdog(void)902 void clocksource_touch_watchdog(void)
903 {
904 	clocksource_resume_watchdog();
905 }
906 
907 /**
908  * clocksource_max_adjustment- Returns max adjustment amount
909  * @cs:         Pointer to clocksource
910  *
911  */
clocksource_max_adjustment(struct clocksource * cs)912 static u32 clocksource_max_adjustment(struct clocksource *cs)
913 {
914 	u64 ret;
915 	/*
916 	 * We won't try to correct for more than 11% adjustments (110,000 ppm),
917 	 */
918 	ret = (u64)cs->mult * 11;
919 	do_div(ret,100);
920 	return (u32)ret;
921 }
922 
923 /**
924  * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
925  * @mult:	cycle to nanosecond multiplier
926  * @shift:	cycle to nanosecond divisor (power of two)
927  * @maxadj:	maximum adjustment value to mult (~11%)
928  * @mask:	bitmask for two's complement subtraction of non 64 bit counters
929  * @max_cyc:	maximum cycle value before potential overflow (does not include
930  *		any safety margin)
931  *
932  * NOTE: This function includes a safety margin of 50%, in other words, we
933  * return half the number of nanoseconds the hardware counter can technically
934  * cover. This is done so that we can potentially detect problems caused by
935  * delayed timers or bad hardware, which might result in time intervals that
936  * are larger than what the math used can handle without overflows.
937  */
clocks_calc_max_nsecs(u32 mult,u32 shift,u32 maxadj,u64 mask,u64 * max_cyc)938 u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
939 {
940 	u64 max_nsecs, max_cycles;
941 
942 	/*
943 	 * Calculate the maximum number of cycles that we can pass to the
944 	 * cyc2ns() function without overflowing a 64-bit result.
945 	 */
946 	max_cycles = ULLONG_MAX;
947 	do_div(max_cycles, mult+maxadj);
948 
949 	/*
950 	 * The actual maximum number of cycles we can defer the clocksource is
951 	 * determined by the minimum of max_cycles and mask.
952 	 * Note: Here we subtract the maxadj to make sure we don't sleep for
953 	 * too long if there's a large negative adjustment.
954 	 */
955 	max_cycles = min(max_cycles, mask);
956 	max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
957 
958 	/* return the max_cycles value as well if requested */
959 	if (max_cyc)
960 		*max_cyc = max_cycles;
961 
962 	/* Return 50% of the actual maximum, so we can detect bad values */
963 	max_nsecs >>= 1;
964 
965 	return max_nsecs;
966 }
967 
968 /**
969  * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
970  * @cs:         Pointer to clocksource to be updated
971  *
972  */
clocksource_update_max_deferment(struct clocksource * cs)973 static inline void clocksource_update_max_deferment(struct clocksource *cs)
974 {
975 	cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
976 						cs->maxadj, cs->mask,
977 						&cs->max_cycles);
978 }
979 
clocksource_find_best(bool oneshot,bool skipcur)980 static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
981 {
982 	struct clocksource *cs;
983 
984 	if (!finished_booting || list_empty(&clocksource_list))
985 		return NULL;
986 
987 	/*
988 	 * We pick the clocksource with the highest rating. If oneshot
989 	 * mode is active, we pick the highres valid clocksource with
990 	 * the best rating.
991 	 */
992 	list_for_each_entry(cs, &clocksource_list, list) {
993 		if (skipcur && cs == curr_clocksource)
994 			continue;
995 		if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
996 			continue;
997 		return cs;
998 	}
999 	return NULL;
1000 }
1001 
__clocksource_select(bool skipcur)1002 static void __clocksource_select(bool skipcur)
1003 {
1004 	bool oneshot = tick_oneshot_mode_active();
1005 	struct clocksource *best, *cs;
1006 
1007 	/* Find the best suitable clocksource */
1008 	best = clocksource_find_best(oneshot, skipcur);
1009 	if (!best)
1010 		return;
1011 
1012 	if (!strlen(override_name))
1013 		goto found;
1014 
1015 	/* Check for the override clocksource. */
1016 	list_for_each_entry(cs, &clocksource_list, list) {
1017 		if (skipcur && cs == curr_clocksource)
1018 			continue;
1019 		if (strcmp(cs->name, override_name) != 0)
1020 			continue;
1021 		/*
1022 		 * Check to make sure we don't switch to a non-highres
1023 		 * capable clocksource if the tick code is in oneshot
1024 		 * mode (highres or nohz)
1025 		 */
1026 		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
1027 			/* Override clocksource cannot be used. */
1028 			if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
1029 				pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
1030 					cs->name);
1031 				override_name[0] = 0;
1032 			} else {
1033 				/*
1034 				 * The override cannot be currently verified.
1035 				 * Deferring to let the watchdog check.
1036 				 */
1037 				pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
1038 					cs->name);
1039 			}
1040 		} else
1041 			/* Override clocksource can be used. */
1042 			best = cs;
1043 		break;
1044 	}
1045 
1046 found:
1047 	if (curr_clocksource != best && !timekeeping_notify(best)) {
1048 		pr_info("Switched to clocksource %s\n", best->name);
1049 		curr_clocksource = best;
1050 	}
1051 }
1052 
1053 /**
1054  * clocksource_select - Select the best clocksource available
1055  *
1056  * Private function. Must hold clocksource_mutex when called.
1057  *
1058  * Select the clocksource with the best rating, or the clocksource,
1059  * which is selected by userspace override.
1060  */
clocksource_select(void)1061 static void clocksource_select(void)
1062 {
1063 	__clocksource_select(false);
1064 }
1065 
clocksource_select_fallback(void)1066 static void clocksource_select_fallback(void)
1067 {
1068 	__clocksource_select(true);
1069 }
1070 
1071 /*
1072  * clocksource_done_booting - Called near the end of core bootup
1073  *
1074  * Hack to avoid lots of clocksource churn at boot time.
1075  * We use fs_initcall because we want this to start before
1076  * device_initcall but after subsys_initcall.
1077  */
clocksource_done_booting(void)1078 static int __init clocksource_done_booting(void)
1079 {
1080 	mutex_lock(&clocksource_mutex);
1081 	curr_clocksource = clocksource_default_clock();
1082 	finished_booting = 1;
1083 	/*
1084 	 * Run the watchdog first to eliminate unstable clock sources
1085 	 */
1086 	__clocksource_watchdog_kthread();
1087 	clocksource_select();
1088 	mutex_unlock(&clocksource_mutex);
1089 	return 0;
1090 }
1091 fs_initcall(clocksource_done_booting);
1092 
1093 /*
1094  * Enqueue the clocksource sorted by rating
1095  */
clocksource_enqueue(struct clocksource * cs)1096 static void clocksource_enqueue(struct clocksource *cs)
1097 {
1098 	struct list_head *entry = &clocksource_list;
1099 	struct clocksource *tmp;
1100 
1101 	list_for_each_entry(tmp, &clocksource_list, list) {
1102 		/* Keep track of the place, where to insert */
1103 		if (tmp->rating < cs->rating)
1104 			break;
1105 		entry = &tmp->list;
1106 	}
1107 	list_add(&cs->list, entry);
1108 }
1109 
1110 /**
1111  * __clocksource_update_freq_scale - Used update clocksource with new freq
1112  * @cs:		clocksource to be registered
1113  * @scale:	Scale factor multiplied against freq to get clocksource hz
1114  * @freq:	clocksource frequency (cycles per second) divided by scale
1115  *
1116  * This should only be called from the clocksource->enable() method.
1117  *
1118  * This *SHOULD NOT* be called directly! Please use the
1119  * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
1120  * functions.
1121  */
__clocksource_update_freq_scale(struct clocksource * cs,u32 scale,u32 freq)1122 void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
1123 {
1124 	u64 sec;
1125 
1126 	/*
1127 	 * Default clocksources are *special* and self-define their mult/shift.
1128 	 * But, you're not special, so you should specify a freq value.
1129 	 */
1130 	if (freq) {
1131 		/*
1132 		 * Calc the maximum number of seconds which we can run before
1133 		 * wrapping around. For clocksources which have a mask > 32-bit
1134 		 * we need to limit the max sleep time to have a good
1135 		 * conversion precision. 10 minutes is still a reasonable
1136 		 * amount. That results in a shift value of 24 for a
1137 		 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
1138 		 * ~ 0.06ppm granularity for NTP.
1139 		 */
1140 		sec = cs->mask;
1141 		do_div(sec, freq);
1142 		do_div(sec, scale);
1143 		if (!sec)
1144 			sec = 1;
1145 		else if (sec > 600 && cs->mask > UINT_MAX)
1146 			sec = 600;
1147 
1148 		clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
1149 				       NSEC_PER_SEC / scale, sec * scale);
1150 	}
1151 
1152 	/*
1153 	 * If the uncertainty margin is not specified, calculate it.
1154 	 * If both scale and freq are non-zero, calculate the clock
1155 	 * period, but bound below at 2*WATCHDOG_MAX_SKEW.  However,
1156 	 * if either of scale or freq is zero, be very conservative and
1157 	 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the
1158 	 * uncertainty margin.  Allow stupidly small uncertainty margins
1159 	 * to be specified by the caller for testing purposes, but warn
1160 	 * to discourage production use of this capability.
1161 	 */
1162 	if (scale && freq && !cs->uncertainty_margin) {
1163 		cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
1164 		if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
1165 			cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
1166 	} else if (!cs->uncertainty_margin) {
1167 		cs->uncertainty_margin = WATCHDOG_THRESHOLD;
1168 	}
1169 	WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);
1170 
1171 	/*
1172 	 * Ensure clocksources that have large 'mult' values don't overflow
1173 	 * when adjusted.
1174 	 */
1175 	cs->maxadj = clocksource_max_adjustment(cs);
1176 	while (freq && ((cs->mult + cs->maxadj < cs->mult)
1177 		|| (cs->mult - cs->maxadj > cs->mult))) {
1178 		cs->mult >>= 1;
1179 		cs->shift--;
1180 		cs->maxadj = clocksource_max_adjustment(cs);
1181 	}
1182 
1183 	/*
1184 	 * Only warn for *special* clocksources that self-define
1185 	 * their mult/shift values and don't specify a freq.
1186 	 */
1187 	WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
1188 		"timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
1189 		cs->name);
1190 
1191 	clocksource_update_max_deferment(cs);
1192 
1193 	pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
1194 		cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
1195 }
1196 EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
1197 
1198 /**
1199  * __clocksource_register_scale - Used to install new clocksources
1200  * @cs:		clocksource to be registered
1201  * @scale:	Scale factor multiplied against freq to get clocksource hz
1202  * @freq:	clocksource frequency (cycles per second) divided by scale
1203  *
1204  * Returns -EBUSY if registration fails, zero otherwise.
1205  *
1206  * This *SHOULD NOT* be called directly! Please use the
1207  * clocksource_register_hz() or clocksource_register_khz helper functions.
1208  */
__clocksource_register_scale(struct clocksource * cs,u32 scale,u32 freq)1209 int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
1210 {
1211 	unsigned long flags;
1212 
1213 	clocksource_arch_init(cs);
1214 
1215 	if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
1216 		cs->id = CSID_GENERIC;
1217 	if (cs->vdso_clock_mode < 0 ||
1218 	    cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
1219 		pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
1220 			cs->name, cs->vdso_clock_mode);
1221 		cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
1222 	}
1223 
1224 	/* Initialize mult/shift and max_idle_ns */
1225 	__clocksource_update_freq_scale(cs, scale, freq);
1226 
1227 	/* Add clocksource to the clocksource list */
1228 	mutex_lock(&clocksource_mutex);
1229 
1230 	clocksource_watchdog_lock(&flags);
1231 	clocksource_enqueue(cs);
1232 	clocksource_enqueue_watchdog(cs);
1233 	clocksource_watchdog_unlock(&flags);
1234 
1235 	clocksource_select();
1236 	clocksource_select_watchdog(false);
1237 	__clocksource_suspend_select(cs);
1238 	mutex_unlock(&clocksource_mutex);
1239 	return 0;
1240 }
1241 EXPORT_SYMBOL_GPL(__clocksource_register_scale);
1242 
__clocksource_change_rating(struct clocksource * cs,int rating)1243 static void __clocksource_change_rating(struct clocksource *cs, int rating)
1244 {
1245 	list_del(&cs->list);
1246 	cs->rating = rating;
1247 	clocksource_enqueue(cs);
1248 }
1249 
1250 /**
1251  * clocksource_change_rating - Change the rating of a registered clocksource
1252  * @cs:		clocksource to be changed
1253  * @rating:	new rating
1254  */
clocksource_change_rating(struct clocksource * cs,int rating)1255 void clocksource_change_rating(struct clocksource *cs, int rating)
1256 {
1257 	unsigned long flags;
1258 
1259 	mutex_lock(&clocksource_mutex);
1260 	clocksource_watchdog_lock(&flags);
1261 	__clocksource_change_rating(cs, rating);
1262 	clocksource_watchdog_unlock(&flags);
1263 
1264 	clocksource_select();
1265 	clocksource_select_watchdog(false);
1266 	clocksource_suspend_select(false);
1267 	mutex_unlock(&clocksource_mutex);
1268 }
1269 EXPORT_SYMBOL(clocksource_change_rating);
1270 
1271 /*
1272  * Unbind clocksource @cs. Called with clocksource_mutex held
1273  */
clocksource_unbind(struct clocksource * cs)1274 static int clocksource_unbind(struct clocksource *cs)
1275 {
1276 	unsigned long flags;
1277 
1278 	if (clocksource_is_watchdog(cs)) {
1279 		/* Select and try to install a replacement watchdog. */
1280 		clocksource_select_watchdog(true);
1281 		if (clocksource_is_watchdog(cs))
1282 			return -EBUSY;
1283 	}
1284 
1285 	if (cs == curr_clocksource) {
1286 		/* Select and try to install a replacement clock source */
1287 		clocksource_select_fallback();
1288 		if (curr_clocksource == cs)
1289 			return -EBUSY;
1290 	}
1291 
1292 	if (clocksource_is_suspend(cs)) {
1293 		/*
1294 		 * Select and try to install a replacement suspend clocksource.
1295 		 * If no replacement suspend clocksource, we will just let the
1296 		 * clocksource go and have no suspend clocksource.
1297 		 */
1298 		clocksource_suspend_select(true);
1299 	}
1300 
1301 	clocksource_watchdog_lock(&flags);
1302 	clocksource_dequeue_watchdog(cs);
1303 	list_del_init(&cs->list);
1304 	clocksource_watchdog_unlock(&flags);
1305 
1306 	return 0;
1307 }
1308 
1309 /**
1310  * clocksource_unregister - remove a registered clocksource
1311  * @cs:	clocksource to be unregistered
1312  */
clocksource_unregister(struct clocksource * cs)1313 int clocksource_unregister(struct clocksource *cs)
1314 {
1315 	int ret = 0;
1316 
1317 	mutex_lock(&clocksource_mutex);
1318 	if (!list_empty(&cs->list))
1319 		ret = clocksource_unbind(cs);
1320 	mutex_unlock(&clocksource_mutex);
1321 	return ret;
1322 }
1323 EXPORT_SYMBOL(clocksource_unregister);
1324 
1325 #ifdef CONFIG_SYSFS
1326 /**
1327  * current_clocksource_show - sysfs interface for current clocksource
1328  * @dev:	unused
1329  * @attr:	unused
1330  * @buf:	char buffer to be filled with clocksource list
1331  *
1332  * Provides sysfs interface for listing current clocksource.
1333  */
current_clocksource_show(struct device * dev,struct device_attribute * attr,char * buf)1334 static ssize_t current_clocksource_show(struct device *dev,
1335 					struct device_attribute *attr,
1336 					char *buf)
1337 {
1338 	ssize_t count = 0;
1339 
1340 	mutex_lock(&clocksource_mutex);
1341 	count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
1342 	mutex_unlock(&clocksource_mutex);
1343 
1344 	return count;
1345 }
1346 
sysfs_get_uname(const char * buf,char * dst,size_t cnt)1347 ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1348 {
1349 	size_t ret = cnt;
1350 
1351 	/* strings from sysfs write are not 0 terminated! */
1352 	if (!cnt || cnt >= CS_NAME_LEN)
1353 		return -EINVAL;
1354 
1355 	/* strip of \n: */
1356 	if (buf[cnt-1] == '\n')
1357 		cnt--;
1358 	if (cnt > 0)
1359 		memcpy(dst, buf, cnt);
1360 	dst[cnt] = 0;
1361 	return ret;
1362 }
1363 
1364 /**
1365  * current_clocksource_store - interface for manually overriding clocksource
1366  * @dev:	unused
1367  * @attr:	unused
1368  * @buf:	name of override clocksource
1369  * @count:	length of buffer
1370  *
1371  * Takes input from sysfs interface for manually overriding the default
1372  * clocksource selection.
1373  */
current_clocksource_store(struct device * dev,struct device_attribute * attr,const char * buf,size_t count)1374 static ssize_t current_clocksource_store(struct device *dev,
1375 					 struct device_attribute *attr,
1376 					 const char *buf, size_t count)
1377 {
1378 	ssize_t ret;
1379 
1380 	mutex_lock(&clocksource_mutex);
1381 
1382 	ret = sysfs_get_uname(buf, override_name, count);
1383 	if (ret >= 0)
1384 		clocksource_select();
1385 
1386 	mutex_unlock(&clocksource_mutex);
1387 
1388 	return ret;
1389 }
1390 static DEVICE_ATTR_RW(current_clocksource);
1391 
1392 /**
1393  * unbind_clocksource_store - interface for manually unbinding clocksource
1394  * @dev:	unused
1395  * @attr:	unused
1396  * @buf:	unused
1397  * @count:	length of buffer
1398  *
1399  * Takes input from sysfs interface for manually unbinding a clocksource.
1400  */
unbind_clocksource_store(struct device * dev,struct device_attribute * attr,const char * buf,size_t count)1401 static ssize_t unbind_clocksource_store(struct device *dev,
1402 					struct device_attribute *attr,
1403 					const char *buf, size_t count)
1404 {
1405 	struct clocksource *cs;
1406 	char name[CS_NAME_LEN];
1407 	ssize_t ret;
1408 
1409 	ret = sysfs_get_uname(buf, name, count);
1410 	if (ret < 0)
1411 		return ret;
1412 
1413 	ret = -ENODEV;
1414 	mutex_lock(&clocksource_mutex);
1415 	list_for_each_entry(cs, &clocksource_list, list) {
1416 		if (strcmp(cs->name, name))
1417 			continue;
1418 		ret = clocksource_unbind(cs);
1419 		break;
1420 	}
1421 	mutex_unlock(&clocksource_mutex);
1422 
1423 	return ret ? ret : count;
1424 }
1425 static DEVICE_ATTR_WO(unbind_clocksource);
1426 
1427 /**
1428  * available_clocksource_show - sysfs interface for listing clocksource
1429  * @dev:	unused
1430  * @attr:	unused
1431  * @buf:	char buffer to be filled with clocksource list
1432  *
1433  * Provides sysfs interface for listing registered clocksources
1434  */
available_clocksource_show(struct device * dev,struct device_attribute * attr,char * buf)1435 static ssize_t available_clocksource_show(struct device *dev,
1436 					  struct device_attribute *attr,
1437 					  char *buf)
1438 {
1439 	struct clocksource *src;
1440 	ssize_t count = 0;
1441 
1442 	mutex_lock(&clocksource_mutex);
1443 	list_for_each_entry(src, &clocksource_list, list) {
1444 		/*
1445 		 * Don't show non-HRES clocksource if the tick code is
1446 		 * in one shot mode (highres=on or nohz=on)
1447 		 */
1448 		if (!tick_oneshot_mode_active() ||
1449 		    (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1450 			count += snprintf(buf + count,
1451 				  max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1452 				  "%s ", src->name);
1453 	}
1454 	mutex_unlock(&clocksource_mutex);
1455 
1456 	count += snprintf(buf + count,
1457 			  max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1458 
1459 	return count;
1460 }
1461 static DEVICE_ATTR_RO(available_clocksource);
1462 
1463 static struct attribute *clocksource_attrs[] = {
1464 	&dev_attr_current_clocksource.attr,
1465 	&dev_attr_unbind_clocksource.attr,
1466 	&dev_attr_available_clocksource.attr,
1467 	NULL
1468 };
1469 ATTRIBUTE_GROUPS(clocksource);
1470 
1471 static struct bus_type clocksource_subsys = {
1472 	.name = "clocksource",
1473 	.dev_name = "clocksource",
1474 };
1475 
1476 static struct device device_clocksource = {
1477 	.id	= 0,
1478 	.bus	= &clocksource_subsys,
1479 	.groups	= clocksource_groups,
1480 };
1481 
init_clocksource_sysfs(void)1482 static int __init init_clocksource_sysfs(void)
1483 {
1484 	int error = subsys_system_register(&clocksource_subsys, NULL);
1485 
1486 	if (!error)
1487 		error = device_register(&device_clocksource);
1488 
1489 	return error;
1490 }
1491 
1492 device_initcall(init_clocksource_sysfs);
1493 #endif /* CONFIG_SYSFS */
1494 
1495 /**
1496  * boot_override_clocksource - boot clock override
1497  * @str:	override name
1498  *
1499  * Takes a clocksource= boot argument and uses it
1500  * as the clocksource override name.
1501  */
boot_override_clocksource(char * str)1502 static int __init boot_override_clocksource(char* str)
1503 {
1504 	mutex_lock(&clocksource_mutex);
1505 	if (str)
1506 		strscpy(override_name, str, sizeof(override_name));
1507 	mutex_unlock(&clocksource_mutex);
1508 	return 1;
1509 }
1510 
1511 __setup("clocksource=", boot_override_clocksource);
1512 
1513 /**
1514  * boot_override_clock - Compatibility layer for deprecated boot option
1515  * @str:	override name
1516  *
1517  * DEPRECATED! Takes a clock= boot argument and uses it
1518  * as the clocksource override name
1519  */
boot_override_clock(char * str)1520 static int __init boot_override_clock(char* str)
1521 {
1522 	if (!strcmp(str, "pmtmr")) {
1523 		pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1524 		return boot_override_clocksource("acpi_pm");
1525 	}
1526 	pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1527 	return boot_override_clocksource(str);
1528 }
1529 
1530 __setup("clock=", boot_override_clock);
1531