projects/linux·blob v7.2 · refs

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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 ([email protected])
6 */
7
8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9
10#include <linux/clocksource.h>
11#include <linux/cpu.h>
12#include <linux/delay.h>
13#include <linux/device.h>
14#include <linux/init.h>
15#include <linux/kthread.h>
16#include <linux/module.h>
17#include <linux/prandom.h>
18#include <linux/sched.h>
19#include <linux/tick.h>
20#include <linux/topology.h>
21
22#include "tick-internal.h"
23#include "timekeeping_internal.h"
24
25static void clocksource_enqueue(struct clocksource *cs);
26
27static noinline u64 cycles_to_nsec_safe(struct clocksource *cs, u64 start, u64 end)
28{
29 u64 delta = clocksource_delta(end, start, cs->mask, cs->max_raw_delta);
30
31 if (likely(delta < cs->max_cycles))
32 return clocksource_cyc2ns(delta, cs->mult, cs->shift);
33
34 return mul_u64_u32_shr(delta, cs->mult, cs->shift);
35}
36
37/**
38 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
39 * @mult: pointer to mult variable
40 * @shift: pointer to shift variable
41 * @from: frequency to convert from
42 * @to: frequency to convert to
43 * @maxsec: guaranteed runtime conversion range in seconds
44 *
45 * The function evaluates the shift/mult pair for the scaled math
46 * operations of clocksources and clockevents.
47 *
48 * @to and @from are frequency values in HZ. For clock sources @to is
49 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
50 * event @to is the counter frequency and @from is NSEC_PER_SEC.
51 *
52 * The @maxsec conversion range argument controls the time frame in
53 * seconds which must be covered by the runtime conversion with the
54 * calculated mult and shift factors. This guarantees that no 64bit
55 * overflow happens when the input value of the conversion is
56 * multiplied with the calculated mult factor. Larger ranges may
57 * reduce the conversion accuracy by choosing smaller mult and shift
58 * factors.
59 */
60void
61clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
62{
63 u64 tmp;
64 u32 sft, sftacc= 32;
65
66 /*
67 * Calculate the shift factor which is limiting the conversion
68 * range:
69 */
70 tmp = ((u64)maxsec * from) >> 32;
71 while (tmp) {
72 tmp >>=1;
73 sftacc--;
74 }
75
76 /*
77 * Find the conversion shift/mult pair which has the best
78 * accuracy and fits the maxsec conversion range:
79 */
80 for (sft = 32; sft > 0; sft--) {
81 tmp = (u64) to << sft;
82 tmp += from / 2;
83 do_div(tmp, from);
84 if ((tmp >> sftacc) == 0)
85 break;
86 }
87 *mult = tmp;
88 *shift = sft;
89}
90EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
91
92/*[Clocksource internal variables]---------
93 * curr_clocksource:
94 * currently selected clocksource.
95 * suspend_clocksource:
96 * used to calculate the suspend time.
97 * clocksource_list:
98 * linked list with the registered clocksources
99 * clocksource_mutex:
100 * protects manipulations to curr_clocksource and the clocksource_list
101 * override_name:
102 * Name of the user-specified clocksource.
103 */
104static struct clocksource *curr_clocksource;
105static struct clocksource *suspend_clocksource;
106static LIST_HEAD(clocksource_list);
107static DEFINE_MUTEX(clocksource_mutex);
108static char override_name[CS_NAME_LEN];
109static int finished_booting;
110static u64 suspend_start;
111
112#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
113static void clocksource_watchdog_work(struct work_struct *work);
114static void clocksource_select(void);
115
116static LIST_HEAD(watchdog_list);
117static struct clocksource *watchdog;
118static struct timer_list watchdog_timer;
119static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
120static DEFINE_SPINLOCK(watchdog_lock);
121static int watchdog_running;
122static atomic_t watchdog_reset_pending;
123
124/* Watchdog interval: 0.5sec. */
125#define WATCHDOG_INTERVAL (HZ >> 1)
126#define WATCHDOG_INTERVAL_NS (WATCHDOG_INTERVAL * (NSEC_PER_SEC / HZ))
127
128/* Maximum time between two reference watchdog readouts */
129#define WATCHDOG_READOUT_MAX_NS (50U * NSEC_PER_USEC)
130
131/*
132 * Maximum time between two remote readouts for NUMA=n. On NUMA enabled systems
133 * the timeout is calculated from the numa distance.
134 */
135#define WATCHDOG_DEFAULT_TIMEOUT_NS (50U * NSEC_PER_USEC)
136
137/*
138 * Remote timeout NUMA distance multiplier. The local distance is 10. The
139 * default remote distance is 20. ACPI tables provide more accurate numbers
140 * which are guaranteed to be greater than the local distance.
141 *
142 * This results in a 5us base value, which is equivalent to the above !NUMA
143 * default.
144 */
145#define WATCHDOG_NUMA_MULTIPLIER_NS ((u64)(WATCHDOG_DEFAULT_TIMEOUT_NS / LOCAL_DISTANCE))
146
147/* Limit the NUMA timeout in case the distance values are insanely big */
148#define WATCHDOG_NUMA_MAX_TIMEOUT_NS ((u64)(500U * NSEC_PER_USEC))
149
150/* Shift values to calculate the approximate $N ppm of a given delta. */
151#define SHIFT_500PPM 11
152#define SHIFT_4000PPM 8
153
154/* Number of attempts to read the watchdog */
155#define WATCHDOG_FREQ_RETRIES 3
156
157/* Five reads local and remote for inter CPU skew detection */
158#define WATCHDOG_REMOTE_MAX_SEQ 10
159
160static inline void clocksource_watchdog_lock(unsigned long *flags)
161{
162 spin_lock_irqsave(&watchdog_lock, *flags);
163}
164
165static inline void clocksource_watchdog_unlock(unsigned long *flags)
166{
167 spin_unlock_irqrestore(&watchdog_lock, *flags);
168}
169
170static int clocksource_watchdog_kthread(void *data);
171
172static void clocksource_watchdog_work(struct work_struct *work)
173{
174 /*
175 * We cannot directly run clocksource_watchdog_kthread() here, because
176 * clocksource_select() calls timekeeping_notify() which uses
177 * stop_machine(). One cannot use stop_machine() from a workqueue() due
178 * lock inversions wrt CPU hotplug.
179 *
180 * Also, we only ever run this work once or twice during the lifetime
181 * of the kernel, so there is no point in creating a more permanent
182 * kthread for this.
183 *
184 * If kthread_run fails the next watchdog scan over the
185 * watchdog_list will find the unstable clock again.
186 */
187 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
188}
189
190static void clocksource_change_rating(struct clocksource *cs, int rating)
191{
192 list_del(&cs->list);
193 cs->rating = rating;
194 clocksource_enqueue(cs);
195}
196
197static void __clocksource_unstable(struct clocksource *cs)
198{
199 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
200 cs->flags |= CLOCK_SOURCE_UNSTABLE;
201
202 /*
203 * If the clocksource is registered clocksource_watchdog_kthread() will
204 * re-rate and re-select.
205 */
206 if (list_empty(&cs->list)) {
207 cs->rating = 0;
208 return;
209 }
210
211 if (cs->mark_unstable)
212 cs->mark_unstable(cs);
213
214 /* kick clocksource_watchdog_kthread() */
215 if (finished_booting)
216 schedule_work(&watchdog_work);
217}
218
219/**
220 * clocksource_mark_unstable - mark clocksource unstable via watchdog
221 * @cs: clocksource to be marked unstable
222 *
223 * This function is called by the x86 TSC code to mark clocksources as unstable;
224 * it defers demotion and re-selection to a kthread.
225 */
226void clocksource_mark_unstable(struct clocksource *cs)
227{
228 unsigned long flags;
229
230 spin_lock_irqsave(&watchdog_lock, flags);
231 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
232 if (!list_empty(&cs->list) && list_empty(&cs->wd_list))
233 list_add(&cs->wd_list, &watchdog_list);
234 __clocksource_unstable(cs);
235 }
236 spin_unlock_irqrestore(&watchdog_lock, flags);
237}
238
239static inline void clocksource_reset_watchdog(void)
240{
241 struct clocksource *cs;
242
243 list_for_each_entry(cs, &watchdog_list, wd_list)
244 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
245}
246
247enum wd_result {
248 WD_SUCCESS,
249 WD_FREQ_NO_WATCHDOG,
250 WD_FREQ_TIMEOUT,
251 WD_FREQ_RESET,
252 WD_FREQ_SKEWED,
253 WD_CPU_TIMEOUT,
254 WD_CPU_SKEWED,
255};
256
257struct watchdog_cpu_data {
258 /* Keep first as it is 32 byte aligned */
259 call_single_data_t csd;
260 atomic_t remote_inprogress;
261 enum wd_result result;
262 u64 cpu_ts[2];
263 struct clocksource *cs;
264 /* Ensure that the sequence is in a separate cache line */
265 atomic_t seq ____cacheline_aligned;
266 /* Set by the control CPU according to NUMA distance */
267 u64 timeout_ns;
268};
269
270struct watchdog_data {
271 raw_spinlock_t lock;
272 enum wd_result result;
273
274 u64 wd_seq;
275 u64 wd_delta;
276 u64 cs_delta;
277 u64 cpu_ts[2];
278
279 unsigned int curr_cpu;
280} ____cacheline_aligned_in_smp;
281
282static void watchdog_check_skew_remote(void *unused);
283
284static DEFINE_PER_CPU_ALIGNED(struct watchdog_cpu_data, watchdog_cpu_data) = {
285 .csd = CSD_INIT(watchdog_check_skew_remote, NULL),
286};
287
288static struct watchdog_data watchdog_data = {
289 .lock = __RAW_SPIN_LOCK_UNLOCKED(watchdog_data.lock),
290};
291
292static inline void watchdog_set_result(struct watchdog_cpu_data *wd, enum wd_result result)
293{
294 guard(raw_spinlock)(&watchdog_data.lock);
295 if (!wd->result) {
296 atomic_set(&wd->seq, WATCHDOG_REMOTE_MAX_SEQ);
297 WRITE_ONCE(wd->result, result);
298 }
299}
300
301/* Wait for the sequence number to hand over control. */
302static bool watchdog_wait_seq(struct watchdog_cpu_data *wd, u64 start, int seq)
303{
304 for(int cnt = 0; atomic_read(&wd->seq) < seq; cnt++) {
305 /* Bail if the other side set an error result */
306 if (READ_ONCE(wd->result) != WD_SUCCESS)
307 return false;
308
309 /* Prevent endless loops if the other CPU does not react. */
310 if (cnt == 5000) {
311 u64 nsecs = ktime_get_raw_fast_ns();
312
313 if (nsecs - start >=wd->timeout_ns) {
314 watchdog_set_result(wd, WD_CPU_TIMEOUT);
315 return false;
316 }
317 cnt = 0;
318 }
319 cpu_relax();
320 }
321 return seq < WATCHDOG_REMOTE_MAX_SEQ;
322}
323
324static void watchdog_check_skew(struct watchdog_cpu_data *wd, int index)
325{
326 u64 prev, now, delta, start = ktime_get_raw_fast_ns();
327 int local = index, remote = (index + 1) & 0x1;
328 struct clocksource *cs = wd->cs;
329
330 /* Set the local timestamp so that the first iteration works correctly */
331 wd->cpu_ts[local] = cs->read(cs);
332
333 /* Signal arrival */
334 atomic_inc(&wd->seq);
335
336 for (int seq = local + 2; seq < WATCHDOG_REMOTE_MAX_SEQ; seq += 2) {
337 if (!watchdog_wait_seq(wd, start, seq))
338 return;
339
340 /* Capture local timestamp before possible non-local coherency overhead */
341 now = cs->read(cs);
342
343 /* Store local timestamp before reading remote to limit coherency stalls */
344 wd->cpu_ts[local] = now;
345
346 prev = wd->cpu_ts[remote];
347 delta = (now - prev) & cs->mask;
348
349 if (delta > cs->max_raw_delta) {
350 watchdog_set_result(wd, WD_CPU_SKEWED);
351 return;
352 }
353
354 /* Hand over to the remote CPU */
355 atomic_inc(&wd->seq);
356 }
357}
358
359static void watchdog_check_skew_remote(void *unused)
360{
361 struct watchdog_cpu_data *wd = this_cpu_ptr(&watchdog_cpu_data);
362
363 atomic_inc(&wd->remote_inprogress);
364 watchdog_check_skew(wd, 1);
365 atomic_dec(&wd->remote_inprogress);
366}
367
368static inline bool wd_csd_locked(struct watchdog_cpu_data *wd)
369{
370 return READ_ONCE(wd->csd.node.u_flags) & CSD_FLAG_LOCK;
371}
372
373/*
374 * This is only invoked for remote CPUs. See watchdog_check_cpu_skew().
375 */
376static inline u64 wd_get_remote_timeout(unsigned int remote_cpu)
377{
378 unsigned int n1, n2;
379 u64 ns;
380
381 if (nr_node_ids == 1)
382 return WATCHDOG_DEFAULT_TIMEOUT_NS;
383
384 n1 = cpu_to_node(smp_processor_id());
385 n2 = cpu_to_node(remote_cpu);
386 ns = WATCHDOG_NUMA_MULTIPLIER_NS * node_distance(n1, n2);
387 return min(ns, WATCHDOG_NUMA_MAX_TIMEOUT_NS);
388}
389
390static void __watchdog_check_cpu_skew(struct clocksource *cs, unsigned int cpu)
391{
392 struct watchdog_cpu_data *wd;
393
394 wd = per_cpu_ptr(&watchdog_cpu_data, cpu);
395 if (atomic_read(&wd->remote_inprogress) || wd_csd_locked(wd)) {
396 watchdog_data.result = WD_CPU_TIMEOUT;
397 return;
398 }
399
400 atomic_set(&wd->seq, 0);
401 wd->result = WD_SUCCESS;
402 wd->cs = cs;
403 /* Store the current CPU ID for the watchdog test unit */
404 cs->wd_cpu = smp_processor_id();
405
406 wd->timeout_ns = wd_get_remote_timeout(cpu);
407
408 /* Kick the remote CPU into the watchdog function */
409 if (WARN_ON_ONCE(smp_call_function_single_async(cpu, &wd->csd))) {
410 watchdog_data.result = WD_CPU_TIMEOUT;
411 return;
412 }
413
414 scoped_guard(irq)
415 watchdog_check_skew(wd, 0);
416
417 scoped_guard(raw_spinlock_irq, &watchdog_data.lock) {
418 watchdog_data.result = wd->result;
419 memcpy(watchdog_data.cpu_ts, wd->cpu_ts, sizeof(wd->cpu_ts));
420 }
421}
422
423static void watchdog_check_cpu_skew(struct clocksource *cs)
424{
425 unsigned int cpu = watchdog_data.curr_cpu;
426
427 cpu = cpumask_next_wrap(cpu, cpu_online_mask);
428 watchdog_data.curr_cpu = cpu;
429
430 /* Skip the current CPU. Handles num_online_cpus() == 1 as well */
431 if (cpu == smp_processor_id())
432 return;
433
434 /* Don't interfere with the test mechanics */
435 if ((cs->flags & CLOCK_SOURCE_WDTEST) && !(cs->flags & CLOCK_SOURCE_WDTEST_PERCPU))
436 return;
437
438 __watchdog_check_cpu_skew(cs, cpu);
439}
440
441static bool watchdog_check_freq(struct clocksource *cs, bool reset_pending)
442{
443 unsigned int ppm_shift = SHIFT_4000PPM;
444 u64 wd_ts0, wd_ts1, cs_ts;
445
446 watchdog_data.result = WD_SUCCESS;
447 if (!watchdog) {
448 watchdog_data.result = WD_FREQ_NO_WATCHDOG;
449 return false;
450 }
451
452 if (cs->flags & CLOCK_SOURCE_WDTEST_PERCPU)
453 return true;
454
455 /*
456 * If both the clocksource and the watchdog claim they are
457 * calibrated use 500ppm limit. Uncalibrated clocksources need a
458 * larger allowance because thefirmware supplied frequencies can be
459 * way off.
460 */
461 if (watchdog->flags & CLOCK_SOURCE_CALIBRATED && cs->flags & CLOCK_SOURCE_CALIBRATED)
462 ppm_shift = SHIFT_500PPM;
463
464 for (int retries = 0; retries < WATCHDOG_FREQ_RETRIES; retries++) {
465 s64 wd_last, cs_last, wd_seq, wd_delta, cs_delta, max_delta;
466
467 scoped_guard(irq) {
468 wd_ts0 = watchdog->read(watchdog);
469 cs_ts = cs->read(cs);
470 wd_ts1 = watchdog->read(watchdog);
471 }
472
473 wd_last = cs->wd_last;
474 cs_last = cs->cs_last;
475
476 /* Validate the watchdog readout window */
477 wd_seq = cycles_to_nsec_safe(watchdog, wd_ts0, wd_ts1);
478 if (wd_seq > WATCHDOG_READOUT_MAX_NS) {
479 /* Store for printout in case all retries fail */
480 watchdog_data.wd_seq = wd_seq;
481 continue;
482 }
483
484 /* Store for subsequent processing */
485 cs->wd_last = wd_ts0;
486 cs->cs_last = cs_ts;
487
488 /* First round or reset pending? */
489 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) || reset_pending)
490 goto reset;
491
492 /* Calculate the nanosecond deltas from the last invocation */
493 wd_delta = cycles_to_nsec_safe(watchdog, wd_last, wd_ts0);
494 cs_delta = cycles_to_nsec_safe(cs, cs_last, cs_ts);
495
496 watchdog_data.wd_delta = wd_delta;
497 watchdog_data.cs_delta = cs_delta;
498
499 /*
500 * Ensure that the deltas are within the readout limits of
501 * the clocksource and the watchdog. Long delays can cause
502 * clocksources to overflow.
503 */
504 max_delta = max(wd_delta, cs_delta);
505 if (max_delta > cs->max_idle_ns || max_delta > watchdog->max_idle_ns)
506 goto reset;
507
508 /*
509 * Calculate and validate the skew against the allowed PPM
510 * value of the maximum delta plus the watchdog readout
511 * time.
512 */
513 if (abs(wd_delta - cs_delta) < (max_delta >> ppm_shift) + wd_seq)
514 return true;
515
516 watchdog_data.result = WD_FREQ_SKEWED;
517 return false;
518 }
519
520 watchdog_data.result = WD_FREQ_TIMEOUT;
521 return false;
522
523reset:
524 cs->flags |= CLOCK_SOURCE_WATCHDOG;
525 watchdog_data.result = WD_FREQ_RESET;
526 return false;
527}
528
529/* Synchronization for sched clock */
530static void clocksource_tick_stable(struct clocksource *cs)
531{
532 if (cs == curr_clocksource && cs->tick_stable)
533 cs->tick_stable(cs);
534}
535
536/* Conditionaly enable high resolution mode */
537static void clocksource_enable_highres(struct clocksource *cs)
538{
539 if ((cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) ||
540 !(cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) ||
541 !watchdog || !(watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS))
542 return;
543
544 /* Mark it valid for high-res. */
545 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
546
547 /*
548 * Can't schedule work before finished_booting is
549 * true. clocksource_done_booting will take care of it.
550 */
551 if (!finished_booting)
552 return;
553
554 if (cs->flags & CLOCK_SOURCE_WDTEST)
555 return;
556
557 /*
558 * If this is not the current clocksource let the watchdog thread
559 * reselect it. Due to the change to high res this clocksource
560 * might be preferred now. If it is the current clocksource let the
561 * tick code know about that change.
562 */
563 if (cs != curr_clocksource) {
564 cs->flags |= CLOCK_SOURCE_RESELECT;
565 schedule_work(&watchdog_work);
566 } else {
567 tick_clock_notify();
568 }
569}
570
571static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 2);
572
573static void watchdog_print_freq_timeout(struct clocksource *cs)
574{
575 if (!__ratelimit(&ratelimit_state))
576 return;
577 pr_info("Watchdog %s read timed out. Readout sequence took: %lluns\n",
578 watchdog->name, watchdog_data.wd_seq);
579}
580
581static void watchdog_print_freq_skew(struct clocksource *cs)
582{
583 pr_warn("Marking clocksource %s unstable due to frequency skew\n", cs->name);
584 pr_warn("Watchdog %20s interval: %16lluns\n", watchdog->name, watchdog_data.wd_delta);
585 pr_warn("Clocksource %20s interval: %16lluns\n", cs->name, watchdog_data.cs_delta);
586}
587
588static void watchdog_handle_remote_timeout(struct clocksource *cs)
589{
590 pr_info_once("Watchdog remote CPU %u read timed out\n", watchdog_data.curr_cpu);
591}
592
593static void watchdog_print_remote_skew(struct clocksource *cs)
594{
595 pr_warn("Marking clocksource %s unstable due to inter CPU skew\n", cs->name);
596 if (watchdog_data.cpu_ts[0] < watchdog_data.cpu_ts[1]) {
597 pr_warn("CPU%u %16llu < CPU%u %16llu (cycles)\n", smp_processor_id(),
598 watchdog_data.cpu_ts[0], watchdog_data.curr_cpu, watchdog_data.cpu_ts[1]);
599 } else {
600 pr_warn("CPU%u %16llu < CPU%u %16llu (cycles)\n", watchdog_data.curr_cpu,
601 watchdog_data.cpu_ts[1], smp_processor_id(), watchdog_data.cpu_ts[0]);
602 }
603}
604
605static void watchdog_check_result(struct clocksource *cs)
606{
607 switch (watchdog_data.result) {
608 case WD_SUCCESS:
609 clocksource_tick_stable(cs);
610 clocksource_enable_highres(cs);
611 return;
612
613 case WD_FREQ_TIMEOUT:
614 watchdog_print_freq_timeout(cs);
615 /* Try again later and invalidate the reference timestamps. */
616 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
617 return;
618
619 case WD_FREQ_NO_WATCHDOG:
620 case WD_FREQ_RESET:
621 /*
622 * Nothing to do when the reference timestamps were reset
623 * or no watchdog clocksource registered.
624 */
625 return;
626
627 case WD_FREQ_SKEWED:
628 watchdog_print_freq_skew(cs);
629 break;
630
631 case WD_CPU_TIMEOUT:
632 /* Remote check timed out. Try again next cycle. */
633 watchdog_handle_remote_timeout(cs);
634 return;
635
636 case WD_CPU_SKEWED:
637 watchdog_print_remote_skew(cs);
638 break;
639 }
640 __clocksource_unstable(cs);
641}
642
643static void clocksource_watchdog(struct timer_list *unused)
644{
645 struct clocksource *cs;
646 bool reset_pending;
647
648 guard(spinlock)(&watchdog_lock);
649 if (!watchdog_running)
650 return;
651
652 reset_pending = atomic_read(&watchdog_reset_pending);
653
654 list_for_each_entry(cs, &watchdog_list, wd_list) {
655 /* Clocksource already marked unstable? */
656 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
657 if (finished_booting)
658 schedule_work(&watchdog_work);
659 continue;
660 }
661
662 /* Compare against watchdog clocksource if available */
663 if (watchdog_check_freq(cs, reset_pending)) {
664 /* Check for inter CPU skew */
665 watchdog_check_cpu_skew(cs);
666 }
667
668 watchdog_check_result(cs);
669 }
670
671 /* Clear after the full clocksource walk */
672 if (reset_pending)
673 atomic_dec(&watchdog_reset_pending);
674
675 /* Could have been rearmed by a stop/start cycle */
676 if (!timer_pending(&watchdog_timer)) {
677 watchdog_timer.expires += WATCHDOG_INTERVAL;
678 add_timer_local(&watchdog_timer);
679 }
680}
681
682static inline void clocksource_start_watchdog(void)
683{
684 if (watchdog_running || list_empty(&watchdog_list))
685 return;
686 timer_setup(&watchdog_timer, clocksource_watchdog, TIMER_PINNED);
687 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
688
689 add_timer_on(&watchdog_timer, get_boot_cpu_id());
690 watchdog_running = 1;
691}
692
693static inline void clocksource_stop_watchdog(void)
694{
695 if (!watchdog_running || !list_empty(&watchdog_list))
696 return;
697 timer_delete(&watchdog_timer);
698 watchdog_running = 0;
699}
700
701static void clocksource_resume_watchdog(void)
702{
703 atomic_inc(&watchdog_reset_pending);
704}
705
706static void clocksource_enqueue_watchdog(struct clocksource *cs)
707{
708 INIT_LIST_HEAD(&cs->wd_list);
709
710 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
711 /* cs is a clocksource to be watched. */
712 list_add(&cs->wd_list, &watchdog_list);
713 cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
714 } else {
715 /* cs is a watchdog. */
716 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
717 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
718 }
719}
720
721static void clocksource_select_watchdog(bool fallback)
722{
723 struct clocksource *cs, *old_wd;
724 unsigned long flags;
725
726 spin_lock_irqsave(&watchdog_lock, flags);
727 /* save current watchdog */
728 old_wd = watchdog;
729 if (fallback)
730 watchdog = NULL;
731
732 list_for_each_entry(cs, &clocksource_list, list) {
733 /* cs is a clocksource to be watched. */
734 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
735 continue;
736
737 /*
738 * If it's not continuous, don't put the fox in charge of
739 * the henhouse.
740 */
741 if (!(cs->flags & CLOCK_SOURCE_IS_CONTINUOUS))
742 continue;
743
744 /* Skip current if we were requested for a fallback. */
745 if (fallback && cs == old_wd)
746 continue;
747
748 /* Pick the best watchdog. */
749 if (!watchdog || cs->rating > watchdog->rating)
750 watchdog = cs;
751 }
752 /* If we failed to find a fallback restore the old one. */
753 if (!watchdog)
754 watchdog = old_wd;
755
756 /* If we changed the watchdog we need to reset cycles. */
757 if (watchdog != old_wd)
758 clocksource_reset_watchdog();
759
760 /* Check if the watchdog timer needs to be started. */
761 clocksource_start_watchdog();
762 spin_unlock_irqrestore(&watchdog_lock, flags);
763}
764
765static void clocksource_dequeue_watchdog(struct clocksource *cs)
766{
767 if (cs != watchdog) {
768 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
769 /* cs is a watched clocksource. */
770 list_del_init(&cs->wd_list);
771 /* Check if the watchdog timer needs to be stopped. */
772 clocksource_stop_watchdog();
773 }
774 }
775}
776
777static int __clocksource_watchdog_kthread(void)
778{
779 struct clocksource *cs, *tmp;
780 unsigned long flags;
781 int select = 0;
782
783 spin_lock_irqsave(&watchdog_lock, flags);
784 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
785 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
786 list_del_init(&cs->wd_list);
787 clocksource_change_rating(cs, 0);
788 select = 1;
789 }
790 if (cs->flags & CLOCK_SOURCE_RESELECT) {
791 cs->flags &= ~CLOCK_SOURCE_RESELECT;
792 select = 1;
793 }
794 }
795 /* Check if the watchdog timer needs to be stopped. */
796 clocksource_stop_watchdog();
797 spin_unlock_irqrestore(&watchdog_lock, flags);
798
799 return select;
800}
801
802static int clocksource_watchdog_kthread(void *data)
803{
804 mutex_lock(&clocksource_mutex);
805 if (__clocksource_watchdog_kthread())
806 clocksource_select();
807 mutex_unlock(&clocksource_mutex);
808 return 0;
809}
810
811static bool clocksource_is_watchdog(struct clocksource *cs)
812{
813 return cs == watchdog;
814}
815
816#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
817
818static void clocksource_enqueue_watchdog(struct clocksource *cs)
819{
820 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
821 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
822}
823
824static void clocksource_select_watchdog(bool fallback) { }
825static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
826static inline void clocksource_resume_watchdog(void) { }
827static inline int __clocksource_watchdog_kthread(void) { return 0; }
828static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
829void clocksource_mark_unstable(struct clocksource *cs) { }
830
831static inline void clocksource_watchdog_lock(unsigned long *flags) { }
832static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
833
834#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
835
836static bool clocksource_is_suspend(struct clocksource *cs)
837{
838 return cs == suspend_clocksource;
839}
840
841static void __clocksource_suspend_select(struct clocksource *cs)
842{
843 /*
844 * Skip the clocksource which will be stopped in suspend state.
845 */
846 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
847 return;
848
849 /*
850 * The nonstop clocksource can be selected as the suspend clocksource to
851 * calculate the suspend time, so it should not supply suspend/resume
852 * interfaces to suspend the nonstop clocksource when system suspends.
853 */
854 if (cs->suspend || cs->resume) {
855 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
856 cs->name);
857 }
858
859 /* Pick the best rating. */
860 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
861 suspend_clocksource = cs;
862}
863
864/**
865 * clocksource_suspend_select - Select the best clocksource for suspend timing
866 * @fallback: if select a fallback clocksource
867 */
868static void clocksource_suspend_select(bool fallback)
869{
870 struct clocksource *cs, *old_suspend;
871
872 old_suspend = suspend_clocksource;
873 if (fallback)
874 suspend_clocksource = NULL;
875
876 list_for_each_entry(cs, &clocksource_list, list) {
877 /* Skip current if we were requested for a fallback. */
878 if (fallback && cs == old_suspend)
879 continue;
880
881 __clocksource_suspend_select(cs);
882 }
883}
884
885/**
886 * clocksource_start_suspend_timing - Start measuring the suspend timing
887 * @cs: current clocksource from timekeeping
888 * @start_cycles: current cycles from timekeeping
889 *
890 * This function will save the start cycle values of suspend timer to calculate
891 * the suspend time when resuming system.
892 *
893 * This function is called late in the suspend process from timekeeping_suspend(),
894 * that means processes are frozen, non-boot cpus and interrupts are disabled
895 * now. It is therefore possible to start the suspend timer without taking the
896 * clocksource mutex.
897 */
898void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
899{
900 if (!suspend_clocksource)
901 return;
902
903 /*
904 * If current clocksource is the suspend timer, we should use the
905 * tkr_mono.cycle_last value as suspend_start to avoid same reading
906 * from suspend timer.
907 */
908 if (clocksource_is_suspend(cs)) {
909 suspend_start = start_cycles;
910 return;
911 }
912
913 if (suspend_clocksource->enable &&
914 suspend_clocksource->enable(suspend_clocksource)) {
915 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
916 return;
917 }
918
919 suspend_start = suspend_clocksource->read(suspend_clocksource);
920}
921
922/**
923 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
924 * @cs: current clocksource from timekeeping
925 * @cycle_now: current cycles from timekeeping
926 *
927 * This function will calculate the suspend time from suspend timer.
928 *
929 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
930 *
931 * This function is called early in the resume process from timekeeping_resume(),
932 * that means there is only one cpu, no processes are running and the interrupts
933 * are disabled. It is therefore possible to stop the suspend timer without
934 * taking the clocksource mutex.
935 */
936u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
937{
938 u64 now, nsec = 0;
939
940 if (!suspend_clocksource)
941 return 0;
942
943 /*
944 * If current clocksource is the suspend timer, we should use the
945 * tkr_mono.cycle_last value from timekeeping as current cycle to
946 * avoid same reading from suspend timer.
947 */
948 if (clocksource_is_suspend(cs))
949 now = cycle_now;
950 else
951 now = suspend_clocksource->read(suspend_clocksource);
952
953 if (now > suspend_start)
954 nsec = cycles_to_nsec_safe(suspend_clocksource, suspend_start, now);
955
956 /*
957 * Disable the suspend timer to save power if current clocksource is
958 * not the suspend timer.
959 */
960 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
961 suspend_clocksource->disable(suspend_clocksource);
962
963 return nsec;
964}
965
966/**
967 * clocksource_suspend - suspend the clocksource(s)
968 */
969void clocksource_suspend(void)
970{
971 struct clocksource *cs;
972
973 list_for_each_entry_reverse(cs, &clocksource_list, list)
974 if (cs->suspend)
975 cs->suspend(cs);
976}
977
978/**
979 * clocksource_resume - resume the clocksource(s)
980 */
981void clocksource_resume(void)
982{
983 struct clocksource *cs;
984
985 list_for_each_entry(cs, &clocksource_list, list)
986 if (cs->resume)
987 cs->resume(cs);
988
989 clocksource_resume_watchdog();
990}
991
992/**
993 * clocksource_touch_watchdog - Update watchdog
994 *
995 * Update the watchdog after exception contexts such as kgdb so as not
996 * to incorrectly trip the watchdog. This might fail when the kernel
997 * was stopped in code which holds watchdog_lock.
998 */
999void clocksource_touch_watchdog(void)
1000{
1001 clocksource_resume_watchdog();
1002}
1003
1004/**
1005 * clocksource_max_adjustment- Returns max adjustment amount
1006 * @cs: Pointer to clocksource
1007 *
1008 */
1009static u32 clocksource_max_adjustment(struct clocksource *cs)
1010{
1011 u64 ret;
1012 /*
1013 * We won't try to correct for more than 11% adjustments (110,000 ppm),
1014 */
1015 ret = (u64)cs->mult * 11;
1016 do_div(ret,100);
1017 return (u32)ret;
1018}
1019
1020/**
1021 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
1022 * @mult: cycle to nanosecond multiplier
1023 * @shift: cycle to nanosecond divisor (power of two)
1024 * @maxadj: maximum adjustment value to mult (~11%)
1025 * @mask: bitmask for two's complement subtraction of non 64 bit counters
1026 * @max_cyc: maximum cycle value before potential overflow (does not include
1027 * any safety margin)
1028 *
1029 * NOTE: This function includes a safety margin of 50%, in other words, we
1030 * return half the number of nanoseconds the hardware counter can technically
1031 * cover. This is done so that we can potentially detect problems caused by
1032 * delayed timers or bad hardware, which might result in time intervals that
1033 * are larger than what the math used can handle without overflows.
1034 */
1035u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
1036{
1037 u64 max_nsecs, max_cycles;
1038
1039 /*
1040 * Calculate the maximum number of cycles that we can pass to the
1041 * cyc2ns() function without overflowing a 64-bit result.
1042 */
1043 max_cycles = ULLONG_MAX;
1044 do_div(max_cycles, mult+maxadj);
1045
1046 /*
1047 * The actual maximum number of cycles we can defer the clocksource is
1048 * determined by the minimum of max_cycles and mask.
1049 * Note: Here we subtract the maxadj to make sure we don't sleep for
1050 * too long if there's a large negative adjustment.
1051 */
1052 max_cycles = min(max_cycles, mask);
1053 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
1054
1055 /* return the max_cycles value as well if requested */
1056 if (max_cyc)
1057 *max_cyc = max_cycles;
1058
1059 /* Return 50% of the actual maximum, so we can detect bad values */
1060 max_nsecs >>= 1;
1061
1062 return max_nsecs;
1063}
1064
1065/**
1066 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
1067 * @cs: Pointer to clocksource to be updated
1068 *
1069 */
1070static inline void clocksource_update_max_deferment(struct clocksource *cs)
1071{
1072 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
1073 cs->maxadj, cs->mask,
1074 &cs->max_cycles);
1075
1076 /*
1077 * Threshold for detecting negative motion in clocksource_delta().
1078 *
1079 * Allow for 0.875 of the counter width so that overly long idle
1080 * sleeps, which go slightly over mask/2, do not trigger the
1081 * negative motion detection.
1082 */
1083 cs->max_raw_delta = (cs->mask >> 1) + (cs->mask >> 2) + (cs->mask >> 3);
1084}
1085
1086static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
1087{
1088 struct clocksource *cs;
1089
1090 if (!finished_booting || list_empty(&clocksource_list))
1091 return NULL;
1092
1093 /*
1094 * We pick the clocksource with the highest rating. If oneshot
1095 * mode is active, we pick the highres valid clocksource with
1096 * the best rating.
1097 */
1098 list_for_each_entry(cs, &clocksource_list, list) {
1099 if (skipcur && cs == curr_clocksource)
1100 continue;
1101 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1102 continue;
1103 if (cs->flags & CLOCK_SOURCE_WDTEST)
1104 continue;
1105 return cs;
1106 }
1107 return NULL;
1108}
1109
1110static void __clocksource_select(bool skipcur)
1111{
1112 bool oneshot = tick_oneshot_mode_active();
1113 struct clocksource *best, *cs;
1114
1115 /* Find the best suitable clocksource */
1116 best = clocksource_find_best(oneshot, skipcur);
1117 if (!best)
1118 return;
1119
1120 if (!strlen(override_name))
1121 goto found;
1122
1123 /* Check for the override clocksource. */
1124 list_for_each_entry(cs, &clocksource_list, list) {
1125 if (skipcur && cs == curr_clocksource)
1126 continue;
1127 if (strcmp(cs->name, override_name) != 0)
1128 continue;
1129 if (cs->flags & CLOCK_SOURCE_WDTEST)
1130 continue;
1131 /*
1132 * Check to make sure we don't switch to a non-highres
1133 * capable clocksource if the tick code is in oneshot
1134 * mode (highres or nohz)
1135 */
1136 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
1137 /* Override clocksource cannot be used. */
1138 if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
1139 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
1140 cs->name);
1141 override_name[0] = 0;
1142 } else {
1143 /*
1144 * The override cannot be currently verified.
1145 * Deferring to let the watchdog check.
1146 */
1147 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
1148 cs->name);
1149 }
1150 } else
1151 /* Override clocksource can be used. */
1152 best = cs;
1153 break;
1154 }
1155
1156found:
1157 if (curr_clocksource != best && !timekeeping_notify(best)) {
1158 pr_info("Switched to clocksource %s\n", best->name);
1159 curr_clocksource = best;
1160 }
1161}
1162
1163/**
1164 * clocksource_select - Select the best clocksource available
1165 *
1166 * Private function. Must hold clocksource_mutex when called.
1167 *
1168 * Select the clocksource with the best rating, or the clocksource,
1169 * which is selected by userspace override.
1170 */
1171static void clocksource_select(void)
1172{
1173 __clocksource_select(false);
1174}
1175
1176static void clocksource_select_fallback(void)
1177{
1178 __clocksource_select(true);
1179}
1180
1181/*
1182 * clocksource_done_booting - Called near the end of core bootup
1183 *
1184 * Hack to avoid lots of clocksource churn at boot time.
1185 * We use fs_initcall because we want this to start before
1186 * device_initcall but after subsys_initcall.
1187 */
1188static int __init clocksource_done_booting(void)
1189{
1190 mutex_lock(&clocksource_mutex);
1191 curr_clocksource = clocksource_default_clock();
1192 finished_booting = 1;
1193 /*
1194 * Run the watchdog first to eliminate unstable clock sources
1195 */
1196 __clocksource_watchdog_kthread();
1197 clocksource_select();
1198 mutex_unlock(&clocksource_mutex);
1199 return 0;
1200}
1201fs_initcall(clocksource_done_booting);
1202
1203/*
1204 * Enqueue the clocksource sorted by rating
1205 */
1206static void clocksource_enqueue(struct clocksource *cs)
1207{
1208 struct list_head *entry = &clocksource_list;
1209 struct clocksource *tmp;
1210
1211 list_for_each_entry(tmp, &clocksource_list, list) {
1212 /* Keep track of the place, where to insert */
1213 if (tmp->rating < cs->rating)
1214 break;
1215 entry = &tmp->list;
1216 }
1217 list_add(&cs->list, entry);
1218}
1219
1220/**
1221 * __clocksource_update_freq_scale - Used update clocksource with new freq
1222 * @cs: clocksource to be registered
1223 * @scale: Scale factor multiplied against freq to get clocksource hz
1224 * @freq: clocksource frequency (cycles per second) divided by scale
1225 */
1226static void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
1227{
1228 u64 sec;
1229
1230 /*
1231 * Default clocksources are *special* and self-define their mult/shift.
1232 * But, you're not special, so you should specify a freq value.
1233 */
1234 if (freq) {
1235 /*
1236 * Calc the maximum number of seconds which we can run before
1237 * wrapping around. For clocksources which have a mask > 32-bit
1238 * we need to limit the max sleep time to have a good
1239 * conversion precision. 10 minutes is still a reasonable
1240 * amount. That results in a shift value of 24 for a
1241 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
1242 * ~ 0.06ppm granularity for NTP.
1243 */
1244 sec = cs->mask;
1245 do_div(sec, freq);
1246 do_div(sec, scale);
1247 if (!sec)
1248 sec = 1;
1249 else if (sec > 600 && cs->mask > UINT_MAX)
1250 sec = 600;
1251
1252 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
1253 NSEC_PER_SEC / scale, sec * scale);
1254
1255 /* Update cs::freq_khz */
1256 cs->freq_khz = div_u64((u64)freq * scale, 1000);
1257 }
1258
1259 /*
1260 * Ensure clocksources that have large 'mult' values don't overflow
1261 * when adjusted.
1262 */
1263 cs->maxadj = clocksource_max_adjustment(cs);
1264 while (freq && ((cs->mult + cs->maxadj < cs->mult)
1265 || (cs->mult - cs->maxadj > cs->mult))) {
1266 cs->mult >>= 1;
1267 cs->shift--;
1268 cs->maxadj = clocksource_max_adjustment(cs);
1269 }
1270
1271 /*
1272 * Only warn for *special* clocksources that self-define
1273 * their mult/shift values and don't specify a freq.
1274 */
1275 WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
1276 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
1277 cs->name);
1278
1279 clocksource_update_max_deferment(cs);
1280
1281 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
1282 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
1283}
1284
1285/**
1286 * __clocksource_register_scale - Used to install new clocksources
1287 * @cs: clocksource to be registered
1288 * @scale: Scale factor multiplied against freq to get clocksource hz
1289 * @freq: clocksource frequency (cycles per second) divided by scale
1290 *
1291 * Returns -EBUSY if registration fails, zero otherwise.
1292 *
1293 * This *SHOULD NOT* be called directly! Please use the
1294 * clocksource_register_hz() or clocksource_register_khz helper functions.
1295 */
1296int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
1297{
1298 unsigned long flags;
1299
1300 clocksource_arch_init(cs);
1301
1302 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
1303 cs->id = CSID_GENERIC;
1304
1305 if (WARN_ON_ONCE(!freq && cs->flags & CLOCK_SOURCE_HAS_COUPLED_CLOCK_EVENT))
1306 cs->flags &= ~CLOCK_SOURCE_HAS_COUPLED_CLOCK_EVENT;
1307
1308 if (cs->vdso_clock_mode < 0 ||
1309 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
1310 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
1311 cs->name, cs->vdso_clock_mode);
1312 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
1313 }
1314
1315 /* Initialize mult/shift and max_idle_ns */
1316 __clocksource_update_freq_scale(cs, scale, freq);
1317
1318 /* Add clocksource to the clocksource list */
1319 mutex_lock(&clocksource_mutex);
1320
1321 clocksource_watchdog_lock(&flags);
1322 clocksource_enqueue(cs);
1323 clocksource_enqueue_watchdog(cs);
1324 clocksource_watchdog_unlock(&flags);
1325
1326 clocksource_select();
1327 clocksource_select_watchdog(false);
1328 __clocksource_suspend_select(cs);
1329 mutex_unlock(&clocksource_mutex);
1330 return 0;
1331}
1332EXPORT_SYMBOL_GPL(__clocksource_register_scale);
1333
1334static void __devm_clocksource_unregister(void *data)
1335{
1336 struct clocksource *cs = data;
1337
1338 clocksource_unregister(cs);
1339}
1340
1341int __devm_clocksource_register_scale(struct device *dev, struct clocksource *cs,
1342 u32 scale, u32 freq)
1343{
1344 int ret;
1345
1346 ret = __clocksource_register_scale(cs, scale, freq);
1347 if (ret)
1348 return ret;
1349
1350 return devm_add_action_or_reset(dev, __devm_clocksource_unregister, cs);
1351}
1352EXPORT_SYMBOL_GPL(__devm_clocksource_register_scale);
1353
1354/*
1355 * Unbind clocksource @cs. Called with clocksource_mutex held
1356 */
1357static int clocksource_unbind(struct clocksource *cs)
1358{
1359 unsigned long flags;
1360
1361 if (clocksource_is_watchdog(cs)) {
1362 /* Select and try to install a replacement watchdog. */
1363 clocksource_select_watchdog(true);
1364 if (clocksource_is_watchdog(cs))
1365 return -EBUSY;
1366 }
1367
1368 if (cs == curr_clocksource) {
1369 /* Select and try to install a replacement clock source */
1370 clocksource_select_fallback();
1371 if (curr_clocksource == cs)
1372 return -EBUSY;
1373 }
1374
1375 if (clocksource_is_suspend(cs)) {
1376 /*
1377 * Select and try to install a replacement suspend clocksource.
1378 * If no replacement suspend clocksource, we will just let the
1379 * clocksource go and have no suspend clocksource.
1380 */
1381 clocksource_suspend_select(true);
1382 }
1383
1384 clocksource_watchdog_lock(&flags);
1385 clocksource_dequeue_watchdog(cs);
1386 list_del_init(&cs->list);
1387 clocksource_watchdog_unlock(&flags);
1388
1389 return 0;
1390}
1391
1392/**
1393 * clocksource_unregister - remove a registered clocksource
1394 * @cs: clocksource to be unregistered
1395 */
1396int clocksource_unregister(struct clocksource *cs)
1397{
1398 int ret = 0;
1399
1400 mutex_lock(&clocksource_mutex);
1401 if (!list_empty(&cs->list))
1402 ret = clocksource_unbind(cs);
1403 mutex_unlock(&clocksource_mutex);
1404 return ret;
1405}
1406EXPORT_SYMBOL(clocksource_unregister);
1407
1408#ifdef CONFIG_SYSFS
1409/**
1410 * current_clocksource_show - sysfs interface for current clocksource
1411 * @dev: unused
1412 * @attr: unused
1413 * @buf: char buffer to be filled with clocksource list
1414 *
1415 * Provides sysfs interface for listing current clocksource.
1416 */
1417static ssize_t current_clocksource_show(struct device *dev,
1418 struct device_attribute *attr,
1419 char *buf)
1420{
1421 ssize_t count = 0;
1422
1423 mutex_lock(&clocksource_mutex);
1424 count = sysfs_emit(buf, "%s\n", curr_clocksource->name);
1425 mutex_unlock(&clocksource_mutex);
1426
1427 return count;
1428}
1429
1430ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1431{
1432 size_t ret = cnt;
1433
1434 /* strings from sysfs write are not 0 terminated! */
1435 if (!cnt || cnt >= CS_NAME_LEN)
1436 return -EINVAL;
1437
1438 /* strip of \n: */
1439 if (buf[cnt-1] == '\n')
1440 cnt--;
1441 if (cnt > 0)
1442 memcpy(dst, buf, cnt);
1443 dst[cnt] = 0;
1444 return ret;
1445}
1446
1447/**
1448 * current_clocksource_store - interface for manually overriding clocksource
1449 * @dev: unused
1450 * @attr: unused
1451 * @buf: name of override clocksource
1452 * @count: length of buffer
1453 *
1454 * Takes input from sysfs interface for manually overriding the default
1455 * clocksource selection.
1456 */
1457static ssize_t current_clocksource_store(struct device *dev,
1458 struct device_attribute *attr,
1459 const char *buf, size_t count)
1460{
1461 ssize_t ret;
1462
1463 mutex_lock(&clocksource_mutex);
1464
1465 ret = sysfs_get_uname(buf, override_name, count);
1466 if (ret >= 0)
1467 clocksource_select();
1468
1469 mutex_unlock(&clocksource_mutex);
1470
1471 return ret;
1472}
1473static DEVICE_ATTR_RW(current_clocksource);
1474
1475/**
1476 * unbind_clocksource_store - interface for manually unbinding clocksource
1477 * @dev: unused
1478 * @attr: unused
1479 * @buf: unused
1480 * @count: length of buffer
1481 *
1482 * Takes input from sysfs interface for manually unbinding a clocksource.
1483 */
1484static ssize_t unbind_clocksource_store(struct device *dev,
1485 struct device_attribute *attr,
1486 const char *buf, size_t count)
1487{
1488 struct clocksource *cs;
1489 char name[CS_NAME_LEN];
1490 ssize_t ret;
1491
1492 ret = sysfs_get_uname(buf, name, count);
1493 if (ret < 0)
1494 return ret;
1495
1496 ret = -ENODEV;
1497 mutex_lock(&clocksource_mutex);
1498 list_for_each_entry(cs, &clocksource_list, list) {
1499 if (strcmp(cs->name, name))
1500 continue;
1501 ret = clocksource_unbind(cs);
1502 break;
1503 }
1504 mutex_unlock(&clocksource_mutex);
1505
1506 return ret ? ret : count;
1507}
1508static DEVICE_ATTR_WO(unbind_clocksource);
1509
1510/**
1511 * available_clocksource_show - sysfs interface for listing clocksource
1512 * @dev: unused
1513 * @attr: unused
1514 * @buf: char buffer to be filled with clocksource list
1515 *
1516 * Provides sysfs interface for listing registered clocksources
1517 */
1518static ssize_t available_clocksource_show(struct device *dev,
1519 struct device_attribute *attr,
1520 char *buf)
1521{
1522 struct clocksource *src;
1523 ssize_t count = 0;
1524
1525 mutex_lock(&clocksource_mutex);
1526 list_for_each_entry(src, &clocksource_list, list) {
1527 /*
1528 * Don't show non-HRES clocksource if the tick code is
1529 * in one shot mode (highres=on or nohz=on)
1530 */
1531 if (!tick_oneshot_mode_active() ||
1532 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1533 count += snprintf(buf + count,
1534 max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1535 "%s ", src->name);
1536 }
1537 mutex_unlock(&clocksource_mutex);
1538
1539 count += snprintf(buf + count,
1540 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1541
1542 return count;
1543}
1544static DEVICE_ATTR_RO(available_clocksource);
1545
1546static struct attribute *clocksource_attrs[] = {
1547 &dev_attr_current_clocksource.attr,
1548 &dev_attr_unbind_clocksource.attr,
1549 &dev_attr_available_clocksource.attr,
1550 NULL
1551};
1552ATTRIBUTE_GROUPS(clocksource);
1553
1554static const struct bus_type clocksource_subsys = {
1555 .name = "clocksource",
1556 .dev_name = "clocksource",
1557};
1558
1559static struct device device_clocksource = {
1560 .id = 0,
1561 .bus = &clocksource_subsys,
1562 .groups = clocksource_groups,
1563};
1564
1565static int __init init_clocksource_sysfs(void)
1566{
1567 int error = subsys_system_register(&clocksource_subsys, NULL);
1568
1569 if (!error)
1570 error = device_register(&device_clocksource);
1571
1572 return error;
1573}
1574
1575device_initcall(init_clocksource_sysfs);
1576#endif /* CONFIG_SYSFS */
1577
1578/**
1579 * boot_override_clocksource - boot clock override
1580 * @str: override name
1581 *
1582 * Takes a clocksource= boot argument and uses it
1583 * as the clocksource override name.
1584 */
1585static int __init boot_override_clocksource(char* str)
1586{
1587 mutex_lock(&clocksource_mutex);
1588 if (str)
1589 strscpy(override_name, str);
1590 mutex_unlock(&clocksource_mutex);
1591 return 1;
1592}
1593
1594__setup("clocksource=", boot_override_clocksource);
1595
1596/**
1597 * boot_override_clock - Compatibility layer for deprecated boot option
1598 * @str: override name
1599 *
1600 * DEPRECATED! Takes a clock= boot argument and uses it
1601 * as the clocksource override name
1602 */
1603static int __init boot_override_clock(char* str)
1604{
1605 if (!strcmp(str, "pmtmr")) {
1606 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
1607 return boot_override_clocksource("acpi_pm");
1608 }
1609 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
1610 return boot_override_clocksource(str);
1611}
1612
1613__setup("clock=", boot_override_clock);