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