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
  23static void clocksource_enqueue(struct clocksource *cs);
 
  24
  25static noinline u64 cycles_to_nsec_safe(struct clocksource *cs, u64 start, u64 end)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  26{
  27	u64 delta = clocksource_delta(end, start, cs->mask, cs->max_raw_delta);
 
  28
  29	if (likely(delta < cs->max_cycles))
  30		return clocksource_cyc2ns(delta, cs->mult, cs->shift);
 
 
 
 
 
 
 
 
 
  31
  32	return mul_u64_u32_shr(delta, cs->mult, cs->shift);
  33}
 
  34
  35/**
  36 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
  37 * @mult:	pointer to mult variable
  38 * @shift:	pointer to shift variable
  39 * @from:	frequency to convert from
  40 * @to:		frequency to convert to
  41 * @maxsec:	guaranteed runtime conversion range in seconds
  42 *
  43 * The function evaluates the shift/mult pair for the scaled math
  44 * operations of clocksources and clockevents.
  45 *
  46 * @to and @from are frequency values in HZ. For clock sources @to is
  47 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
  48 * event @to is the counter frequency and @from is NSEC_PER_SEC.
  49 *
  50 * The @maxsec conversion range argument controls the time frame in
  51 * seconds which must be covered by the runtime conversion with the
  52 * calculated mult and shift factors. This guarantees that no 64bit
  53 * overflow happens when the input value of the conversion is
  54 * multiplied with the calculated mult factor. Larger ranges may
  55 * reduce the conversion accuracy by choosing smaller mult and shift
  56 * factors.
  57 */
  58void
  59clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
  60{
  61	u64 tmp;
  62	u32 sft, sftacc= 32;
  63
  64	/*
  65	 * Calculate the shift factor which is limiting the conversion
  66	 * range:
  67	 */
  68	tmp = ((u64)maxsec * from) >> 32;
  69	while (tmp) {
  70		tmp >>=1;
  71		sftacc--;
  72	}
  73
  74	/*
  75	 * Find the conversion shift/mult pair which has the best
  76	 * accuracy and fits the maxsec conversion range:
  77	 */
  78	for (sft = 32; sft > 0; sft--) {
  79		tmp = (u64) to << sft;
  80		tmp += from / 2;
  81		do_div(tmp, from);
  82		if ((tmp >> sftacc) == 0)
  83			break;
  84	}
  85	*mult = tmp;
  86	*shift = sft;
  87}
  88EXPORT_SYMBOL_GPL(clocks_calc_mult_shift);
  89
  90/*[Clocksource internal variables]---------
  91 * curr_clocksource:
  92 *	currently selected clocksource.
  93 * suspend_clocksource:
  94 *	used to calculate the suspend time.
  95 * clocksource_list:
  96 *	linked list with the registered clocksources
  97 * clocksource_mutex:
  98 *	protects manipulations to curr_clocksource and the clocksource_list
  99 * override_name:
 100 *	Name of the user-specified clocksource.
 101 */
 102static struct clocksource *curr_clocksource;
 103static struct clocksource *suspend_clocksource;
 104static LIST_HEAD(clocksource_list);
 105static DEFINE_MUTEX(clocksource_mutex);
 106static char override_name[CS_NAME_LEN];
 107static int finished_booting;
 108static u64 suspend_start;
 109
 110/*
 111 * Interval: 0.5sec.
 112 */
 113#define WATCHDOG_INTERVAL (HZ >> 1)
 114#define WATCHDOG_INTERVAL_MAX_NS ((2 * WATCHDOG_INTERVAL) * (NSEC_PER_SEC / HZ))
 115
 116/*
 117 * Threshold: 0.0312s, when doubled: 0.0625s.
 118 */
 119#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5)
 120
 121/*
 122 * Maximum permissible delay between two readouts of the watchdog
 123 * clocksource surrounding a read of the clocksource being validated.
 124 * This delay could be due to SMIs, NMIs, or to VCPU preemptions.  Used as
 125 * a lower bound for cs->uncertainty_margin values when registering clocks.
 126 *
 127 * The default of 500 parts per million is based on NTP's limits.
 128 * If a clocksource is good enough for NTP, it is good enough for us!
 129 *
 130 * In other words, by default, even if a clocksource is extremely
 131 * precise (for example, with a sub-nanosecond period), the maximum
 132 * permissible skew between the clocksource watchdog and the clocksource
 133 * under test is not permitted to go below the 500ppm minimum defined
 134 * by MAX_SKEW_USEC.  This 500ppm minimum may be overridden using the
 135 * CLOCKSOURCE_WATCHDOG_MAX_SKEW_US Kconfig option.
 136 */
 137#ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
 138#define MAX_SKEW_USEC	CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
 139#else
 140#define MAX_SKEW_USEC	(125 * WATCHDOG_INTERVAL / HZ)
 141#endif
 142
 143/*
 144 * Default for maximum permissible skew when cs->uncertainty_margin is
 145 * not specified, and the lower bound even when cs->uncertainty_margin
 146 * is specified.  This is also the default that is used when registering
 147 * clocks with unspecifed cs->uncertainty_margin, so this macro is used
 148 * even in CONFIG_CLOCKSOURCE_WATCHDOG=n kernels.
 149 */
 150#define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC)
 151
 152#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
 153static void clocksource_watchdog_work(struct work_struct *work);
 154static void clocksource_select(void);
 155
 156static LIST_HEAD(watchdog_list);
 157static struct clocksource *watchdog;
 158static struct timer_list watchdog_timer;
 159static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
 160static DEFINE_SPINLOCK(watchdog_lock);
 161static int watchdog_running;
 162static atomic_t watchdog_reset_pending;
 163static int64_t watchdog_max_interval;
 164
 165static inline void clocksource_watchdog_lock(unsigned long *flags)
 166{
 167	spin_lock_irqsave(&watchdog_lock, *flags);
 168}
 169
 170static inline void clocksource_watchdog_unlock(unsigned long *flags)
 171{
 172	spin_unlock_irqrestore(&watchdog_lock, *flags);
 173}
 174
 175static int clocksource_watchdog_kthread(void *data);
 
 
 
 
 
 
 
 176
 177static void clocksource_watchdog_work(struct work_struct *work)
 178{
 179	/*
 180	 * We cannot directly run clocksource_watchdog_kthread() here, because
 181	 * clocksource_select() calls timekeeping_notify() which uses
 182	 * stop_machine(). One cannot use stop_machine() from a workqueue() due
 183	 * lock inversions wrt CPU hotplug.
 184	 *
 185	 * Also, we only ever run this work once or twice during the lifetime
 186	 * of the kernel, so there is no point in creating a more permanent
 187	 * kthread for this.
 188	 *
 189	 * If kthread_run fails the next watchdog scan over the
 190	 * watchdog_list will find the unstable clock again.
 191	 */
 192	kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
 193}
 194
 195static void clocksource_change_rating(struct clocksource *cs, int rating)
 196{
 197	list_del(&cs->list);
 198	cs->rating = rating;
 199	clocksource_enqueue(cs);
 200}
 201
 202static void __clocksource_unstable(struct clocksource *cs)
 203{
 204	cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
 205	cs->flags |= CLOCK_SOURCE_UNSTABLE;
 206
 207	/*
 208	 * If the clocksource is registered clocksource_watchdog_kthread() will
 209	 * re-rate and re-select.
 210	 */
 211	if (list_empty(&cs->list)) {
 212		cs->rating = 0;
 213		return;
 214	}
 215
 216	if (cs->mark_unstable)
 217		cs->mark_unstable(cs);
 218
 219	/* kick clocksource_watchdog_kthread() */
 220	if (finished_booting)
 221		schedule_work(&watchdog_work);
 222}
 223
 
 
 
 
 
 
 
 224/**
 225 * clocksource_mark_unstable - mark clocksource unstable via watchdog
 226 * @cs:		clocksource to be marked unstable
 227 *
 228 * This function is called by the x86 TSC code to mark clocksources as unstable;
 229 * it defers demotion and re-selection to a kthread.
 
 
 230 */
 231void clocksource_mark_unstable(struct clocksource *cs)
 232{
 233	unsigned long flags;
 234
 235	spin_lock_irqsave(&watchdog_lock, flags);
 236	if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
 237		if (!list_empty(&cs->list) && list_empty(&cs->wd_list))
 238			list_add(&cs->wd_list, &watchdog_list);
 239		__clocksource_unstable(cs);
 240	}
 241	spin_unlock_irqrestore(&watchdog_lock, flags);
 242}
 243
 244static int verify_n_cpus = 8;
 245module_param(verify_n_cpus, int, 0644);
 246
 247enum wd_read_status {
 248	WD_READ_SUCCESS,
 249	WD_READ_UNSTABLE,
 250	WD_READ_SKIP
 251};
 252
 253static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow)
 254{
 255	int64_t md = 2 * watchdog->uncertainty_margin;
 256	unsigned int nretries, max_retries;
 257	int64_t wd_delay, wd_seq_delay;
 258	u64 wd_end, wd_end2;
 259
 260	max_retries = clocksource_get_max_watchdog_retry();
 261	for (nretries = 0; nretries <= max_retries; nretries++) {
 262		local_irq_disable();
 263		*wdnow = watchdog->read(watchdog);
 264		*csnow = cs->read(cs);
 265		wd_end = watchdog->read(watchdog);
 266		wd_end2 = watchdog->read(watchdog);
 267		local_irq_enable();
 268
 269		wd_delay = cycles_to_nsec_safe(watchdog, *wdnow, wd_end);
 270		if (wd_delay <= md + cs->uncertainty_margin) {
 271			if (nretries > 1 && nretries >= max_retries) {
 272				pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n",
 273					smp_processor_id(), watchdog->name, nretries);
 274			}
 275			return WD_READ_SUCCESS;
 276		}
 277
 278		/*
 279		 * Now compute delay in consecutive watchdog read to see if
 280		 * there is too much external interferences that cause
 281		 * significant delay in reading both clocksource and watchdog.
 282		 *
 283		 * If consecutive WD read-back delay > md, report
 284		 * system busy, reinit the watchdog and skip the current
 285		 * watchdog test.
 286		 */
 287		wd_seq_delay = cycles_to_nsec_safe(watchdog, wd_end, wd_end2);
 288		if (wd_seq_delay > md)
 289			goto skip_test;
 290	}
 291
 292	pr_warn("timekeeping watchdog on CPU%d: wd-%s-wd excessive read-back delay of %lldns vs. limit of %ldns, wd-wd read-back delay only %lldns, attempt %d, marking %s unstable\n",
 293		smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name);
 294	return WD_READ_UNSTABLE;
 295
 296skip_test:
 297	pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n",
 298		smp_processor_id(), watchdog->name, wd_seq_delay);
 299	pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n",
 300		cs->name, wd_delay);
 301	return WD_READ_SKIP;
 302}
 303
 304static u64 csnow_mid;
 305static cpumask_t cpus_ahead;
 306static cpumask_t cpus_behind;
 307static cpumask_t cpus_chosen;
 308
 309static void clocksource_verify_choose_cpus(void)
 310{
 311	int cpu, i, n = verify_n_cpus;
 312
 313	if (n < 0) {
 314		/* Check all of the CPUs. */
 315		cpumask_copy(&cpus_chosen, cpu_online_mask);
 316		cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
 317		return;
 318	}
 319
 320	/* If no checking desired, or no other CPU to check, leave. */
 321	cpumask_clear(&cpus_chosen);
 322	if (n == 0 || num_online_cpus() <= 1)
 323		return;
 324
 325	/* Make sure to select at least one CPU other than the current CPU. */
 326	cpu = cpumask_first(cpu_online_mask);
 327	if (cpu == smp_processor_id())
 328		cpu = cpumask_next(cpu, cpu_online_mask);
 329	if (WARN_ON_ONCE(cpu >= nr_cpu_ids))
 330		return;
 331	cpumask_set_cpu(cpu, &cpus_chosen);
 332
 333	/* Force a sane value for the boot parameter. */
 334	if (n > nr_cpu_ids)
 335		n = nr_cpu_ids;
 336
 337	/*
 338	 * Randomly select the specified number of CPUs.  If the same
 339	 * CPU is selected multiple times, that CPU is checked only once,
 340	 * and no replacement CPU is selected.  This gracefully handles
 341	 * situations where verify_n_cpus is greater than the number of
 342	 * CPUs that are currently online.
 343	 */
 344	for (i = 1; i < n; i++) {
 345		cpu = get_random_u32_below(nr_cpu_ids);
 346		cpu = cpumask_next(cpu - 1, cpu_online_mask);
 347		if (cpu >= nr_cpu_ids)
 348			cpu = cpumask_first(cpu_online_mask);
 349		if (!WARN_ON_ONCE(cpu >= nr_cpu_ids))
 350			cpumask_set_cpu(cpu, &cpus_chosen);
 351	}
 352
 353	/* Don't verify ourselves. */
 354	cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);
 355}
 356
 357static void clocksource_verify_one_cpu(void *csin)
 358{
 359	struct clocksource *cs = (struct clocksource *)csin;
 360
 361	csnow_mid = cs->read(cs);
 362}
 363
 364void clocksource_verify_percpu(struct clocksource *cs)
 365{
 366	int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX;
 367	u64 csnow_begin, csnow_end;
 368	int cpu, testcpu;
 369	s64 delta;
 370
 371	if (verify_n_cpus == 0)
 372		return;
 373	cpumask_clear(&cpus_ahead);
 374	cpumask_clear(&cpus_behind);
 375	cpus_read_lock();
 376	migrate_disable();
 377	clocksource_verify_choose_cpus();
 378	if (cpumask_empty(&cpus_chosen)) {
 379		migrate_enable();
 380		cpus_read_unlock();
 381		pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name);
 382		return;
 383	}
 384	testcpu = smp_processor_id();
 385	pr_info("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n",
 386		cs->name, testcpu, cpumask_pr_args(&cpus_chosen));
 387	preempt_disable();
 388	for_each_cpu(cpu, &cpus_chosen) {
 389		if (cpu == testcpu)
 390			continue;
 391		csnow_begin = cs->read(cs);
 392		smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1);
 393		csnow_end = cs->read(cs);
 394		delta = (s64)((csnow_mid - csnow_begin) & cs->mask);
 395		if (delta < 0)
 396			cpumask_set_cpu(cpu, &cpus_behind);
 397		delta = (csnow_end - csnow_mid) & cs->mask;
 398		if (delta < 0)
 399			cpumask_set_cpu(cpu, &cpus_ahead);
 400		cs_nsec = cycles_to_nsec_safe(cs, csnow_begin, csnow_end);
 401		if (cs_nsec > cs_nsec_max)
 402			cs_nsec_max = cs_nsec;
 403		if (cs_nsec < cs_nsec_min)
 404			cs_nsec_min = cs_nsec;
 405	}
 406	preempt_enable();
 407	migrate_enable();
 408	cpus_read_unlock();
 409	if (!cpumask_empty(&cpus_ahead))
 410		pr_warn("        CPUs %*pbl ahead of CPU %d for clocksource %s.\n",
 411			cpumask_pr_args(&cpus_ahead), testcpu, cs->name);
 412	if (!cpumask_empty(&cpus_behind))
 413		pr_warn("        CPUs %*pbl behind CPU %d for clocksource %s.\n",
 414			cpumask_pr_args(&cpus_behind), testcpu, cs->name);
 415	if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind))
 416		pr_warn("        CPU %d check durations %lldns - %lldns for clocksource %s.\n",
 417			testcpu, cs_nsec_min, cs_nsec_max, cs->name);
 418}
 419EXPORT_SYMBOL_GPL(clocksource_verify_percpu);
 420
 421static inline void clocksource_reset_watchdog(void)
 422{
 423	struct clocksource *cs;
 424
 425	list_for_each_entry(cs, &watchdog_list, wd_list)
 426		cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
 427}
 428
 429
 430static void clocksource_watchdog(struct timer_list *unused)
 431{
 432	int64_t wd_nsec, cs_nsec, interval;
 433	u64 csnow, wdnow, cslast, wdlast;
 434	int next_cpu, reset_pending;
 435	struct clocksource *cs;
 436	enum wd_read_status read_ret;
 437	unsigned long extra_wait = 0;
 438	u32 md;
 439
 440	spin_lock(&watchdog_lock);
 441	if (!watchdog_running)
 442		goto out;
 443
 444	reset_pending = atomic_read(&watchdog_reset_pending);
 445
 446	list_for_each_entry(cs, &watchdog_list, wd_list) {
 447
 448		/* Clocksource already marked unstable? */
 449		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
 450			if (finished_booting)
 451				schedule_work(&watchdog_work);
 452			continue;
 453		}
 454
 455		read_ret = cs_watchdog_read(cs, &csnow, &wdnow);
 456
 457		if (read_ret == WD_READ_UNSTABLE) {
 458			/* Clock readout unreliable, so give it up. */
 459			__clocksource_unstable(cs);
 460			continue;
 461		}
 462
 463		/*
 464		 * When WD_READ_SKIP is returned, it means the system is likely
 465		 * under very heavy load, where the latency of reading
 466		 * watchdog/clocksource is very big, and affect the accuracy of
 467		 * watchdog check. So give system some space and suspend the
 468		 * watchdog check for 5 minutes.
 469		 */
 470		if (read_ret == WD_READ_SKIP) {
 471			/*
 472			 * As the watchdog timer will be suspended, and
 473			 * cs->last could keep unchanged for 5 minutes, reset
 474			 * the counters.
 475			 */
 476			clocksource_reset_watchdog();
 477			extra_wait = HZ * 300;
 478			break;
 479		}
 480
 481		/* Clocksource initialized ? */
 482		if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
 483		    atomic_read(&watchdog_reset_pending)) {
 484			cs->flags |= CLOCK_SOURCE_WATCHDOG;
 485			cs->wd_last = wdnow;
 486			cs->cs_last = csnow;
 487			continue;
 488		}
 489
 490		wd_nsec = cycles_to_nsec_safe(watchdog, cs->wd_last, wdnow);
 491		cs_nsec = cycles_to_nsec_safe(cs, cs->cs_last, csnow);
 492		wdlast = cs->wd_last; /* save these in case we print them */
 493		cslast = cs->cs_last;
 
 494		cs->cs_last = csnow;
 495		cs->wd_last = wdnow;
 496
 497		if (atomic_read(&watchdog_reset_pending))
 498			continue;
 499
 500		/*
 501		 * The processing of timer softirqs can get delayed (usually
 502		 * on account of ksoftirqd not getting to run in a timely
 503		 * manner), which causes the watchdog interval to stretch.
 504		 * Skew detection may fail for longer watchdog intervals
 505		 * on account of fixed margins being used.
 506		 * Some clocksources, e.g. acpi_pm, cannot tolerate
 507		 * watchdog intervals longer than a few seconds.
 508		 */
 509		interval = max(cs_nsec, wd_nsec);
 510		if (unlikely(interval > WATCHDOG_INTERVAL_MAX_NS)) {
 511			if (system_state > SYSTEM_SCHEDULING &&
 512			    interval > 2 * watchdog_max_interval) {
 513				watchdog_max_interval = interval;
 514				pr_warn("Long readout interval, skipping watchdog check: cs_nsec: %lld wd_nsec: %lld\n",
 515					cs_nsec, wd_nsec);
 516			}
 517			watchdog_timer.expires = jiffies;
 518			continue;
 519		}
 520
 521		/* Check the deviation from the watchdog clocksource. */
 522		md = cs->uncertainty_margin + watchdog->uncertainty_margin;
 523		if (abs(cs_nsec - wd_nsec) > md) {
 524			s64 cs_wd_msec;
 525			s64 wd_msec;
 526			u32 wd_rem;
 527
 528			pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n",
 529				smp_processor_id(), cs->name);
 530			pr_warn("                      '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n",
 531				watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask);
 532			pr_warn("                      '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n",
 533				cs->name, cs_nsec, csnow, cslast, cs->mask);
 534			cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem);
 535			wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem);
 536			pr_warn("                      Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n",
 537				cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec);
 538			if (curr_clocksource == cs)
 539				pr_warn("                      '%s' is current clocksource.\n", cs->name);
 540			else if (curr_clocksource)
 541				pr_warn("                      '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name);
 542			else
 543				pr_warn("                      No current clocksource.\n");
 544			__clocksource_unstable(cs);
 545			continue;
 546		}
 547
 548		if (cs == curr_clocksource && cs->tick_stable)
 549			cs->tick_stable(cs);
 550
 551		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
 552		    (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
 553		    (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
 554			/* Mark it valid for high-res. */
 555			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 556
 557			/*
 558			 * clocksource_done_booting() will sort it if
 559			 * finished_booting is not set yet.
 560			 */
 561			if (!finished_booting)
 562				continue;
 563
 564			/*
 565			 * If this is not the current clocksource let
 566			 * the watchdog thread reselect it. Due to the
 567			 * change to high res this clocksource might
 568			 * be preferred now. If it is the current
 569			 * clocksource let the tick code know about
 570			 * that change.
 571			 */
 572			if (cs != curr_clocksource) {
 573				cs->flags |= CLOCK_SOURCE_RESELECT;
 574				schedule_work(&watchdog_work);
 575			} else {
 576				tick_clock_notify();
 577			}
 578		}
 579	}
 580
 581	/*
 582	 * We only clear the watchdog_reset_pending, when we did a
 583	 * full cycle through all clocksources.
 584	 */
 585	if (reset_pending)
 586		atomic_dec(&watchdog_reset_pending);
 587
 588	/*
 589	 * Cycle through CPUs to check if the CPUs stay synchronized
 590	 * to each other.
 591	 */
 592	next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
 593	if (next_cpu >= nr_cpu_ids)
 594		next_cpu = cpumask_first(cpu_online_mask);
 595
 596	/*
 597	 * Arm timer if not already pending: could race with concurrent
 598	 * pair clocksource_stop_watchdog() clocksource_start_watchdog().
 599	 */
 600	if (!timer_pending(&watchdog_timer)) {
 601		watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait;
 602		add_timer_on(&watchdog_timer, next_cpu);
 603	}
 604out:
 605	spin_unlock(&watchdog_lock);
 606}
 607
 608static inline void clocksource_start_watchdog(void)
 609{
 610	if (watchdog_running || !watchdog || list_empty(&watchdog_list))
 611		return;
 612	timer_setup(&watchdog_timer, clocksource_watchdog, 0);
 
 613	watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
 614	add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
 615	watchdog_running = 1;
 616}
 617
 618static inline void clocksource_stop_watchdog(void)
 619{
 620	if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
 621		return;
 622	del_timer(&watchdog_timer);
 623	watchdog_running = 0;
 624}
 625
 
 
 
 
 
 
 
 
 626static void clocksource_resume_watchdog(void)
 627{
 628	atomic_inc(&watchdog_reset_pending);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 629}
 630
 631static void clocksource_enqueue_watchdog(struct clocksource *cs)
 632{
 633	INIT_LIST_HEAD(&cs->wd_list);
 634
 
 635	if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
 636		/* cs is a clocksource to be watched. */
 637		list_add(&cs->wd_list, &watchdog_list);
 638		cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
 639	} else {
 640		/* cs is a watchdog. */
 641		if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 642			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 643	}
 644}
 645
 646static void clocksource_select_watchdog(bool fallback)
 647{
 648	struct clocksource *cs, *old_wd;
 649	unsigned long flags;
 650
 651	spin_lock_irqsave(&watchdog_lock, flags);
 652	/* save current watchdog */
 653	old_wd = watchdog;
 654	if (fallback)
 655		watchdog = NULL;
 656
 657	list_for_each_entry(cs, &clocksource_list, list) {
 658		/* cs is a clocksource to be watched. */
 659		if (cs->flags & CLOCK_SOURCE_MUST_VERIFY)
 660			continue;
 661
 662		/* Skip current if we were requested for a fallback. */
 663		if (fallback && cs == old_wd)
 664			continue;
 665
 666		/* Pick the best watchdog. */
 667		if (!watchdog || cs->rating > watchdog->rating)
 668			watchdog = cs;
 
 
 
 669	}
 670	/* If we failed to find a fallback restore the old one. */
 671	if (!watchdog)
 672		watchdog = old_wd;
 673
 674	/* If we changed the watchdog we need to reset cycles. */
 675	if (watchdog != old_wd)
 676		clocksource_reset_watchdog();
 677
 678	/* Check if the watchdog timer needs to be started. */
 679	clocksource_start_watchdog();
 680	spin_unlock_irqrestore(&watchdog_lock, flags);
 681}
 682
 683static void clocksource_dequeue_watchdog(struct clocksource *cs)
 684{
 685	if (cs != watchdog) {
 686		if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
 687			/* cs is a watched clocksource. */
 688			list_del_init(&cs->wd_list);
 689			/* Check if the watchdog timer needs to be stopped. */
 690			clocksource_stop_watchdog();
 
 
 
 
 
 
 
 
 
 
 
 691		}
 692	}
 
 
 
 
 693}
 694
 695static int __clocksource_watchdog_kthread(void)
 696{
 697	struct clocksource *cs, *tmp;
 698	unsigned long flags;
 699	int select = 0;
 700
 701	/* Do any required per-CPU skew verification. */
 702	if (curr_clocksource &&
 703	    curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE &&
 704	    curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU)
 705		clocksource_verify_percpu(curr_clocksource);
 706
 
 707	spin_lock_irqsave(&watchdog_lock, flags);
 708	list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
 709		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
 710			list_del_init(&cs->wd_list);
 711			clocksource_change_rating(cs, 0);
 712			select = 1;
 713		}
 714		if (cs->flags & CLOCK_SOURCE_RESELECT) {
 715			cs->flags &= ~CLOCK_SOURCE_RESELECT;
 716			select = 1;
 717		}
 718	}
 719	/* Check if the watchdog timer needs to be stopped. */
 720	clocksource_stop_watchdog();
 721	spin_unlock_irqrestore(&watchdog_lock, flags);
 722
 723	return select;
 724}
 725
 726static int clocksource_watchdog_kthread(void *data)
 727{
 728	mutex_lock(&clocksource_mutex);
 729	if (__clocksource_watchdog_kthread())
 730		clocksource_select();
 731	mutex_unlock(&clocksource_mutex);
 732	return 0;
 733}
 734
 735static bool clocksource_is_watchdog(struct clocksource *cs)
 736{
 737	return cs == watchdog;
 738}
 739
 740#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
 741
 742static void clocksource_enqueue_watchdog(struct clocksource *cs)
 743{
 744	if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 745		cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 746}
 747
 748static void clocksource_select_watchdog(bool fallback) { }
 749static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
 750static inline void clocksource_resume_watchdog(void) { }
 751static inline int __clocksource_watchdog_kthread(void) { return 0; }
 752static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
 753void clocksource_mark_unstable(struct clocksource *cs) { }
 754
 755static inline void clocksource_watchdog_lock(unsigned long *flags) { }
 756static inline void clocksource_watchdog_unlock(unsigned long *flags) { }
 757
 758#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
 759
 760static bool clocksource_is_suspend(struct clocksource *cs)
 761{
 762	return cs == suspend_clocksource;
 763}
 764
 765static void __clocksource_suspend_select(struct clocksource *cs)
 766{
 767	/*
 768	 * Skip the clocksource which will be stopped in suspend state.
 769	 */
 770	if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP))
 771		return;
 772
 773	/*
 774	 * The nonstop clocksource can be selected as the suspend clocksource to
 775	 * calculate the suspend time, so it should not supply suspend/resume
 776	 * interfaces to suspend the nonstop clocksource when system suspends.
 777	 */
 778	if (cs->suspend || cs->resume) {
 779		pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n",
 780			cs->name);
 781	}
 782
 783	/* Pick the best rating. */
 784	if (!suspend_clocksource || cs->rating > suspend_clocksource->rating)
 785		suspend_clocksource = cs;
 786}
 787
 788/**
 789 * clocksource_suspend_select - Select the best clocksource for suspend timing
 790 * @fallback:	if select a fallback clocksource
 791 */
 792static void clocksource_suspend_select(bool fallback)
 793{
 794	struct clocksource *cs, *old_suspend;
 795
 796	old_suspend = suspend_clocksource;
 797	if (fallback)
 798		suspend_clocksource = NULL;
 799
 800	list_for_each_entry(cs, &clocksource_list, list) {
 801		/* Skip current if we were requested for a fallback. */
 802		if (fallback && cs == old_suspend)
 803			continue;
 804
 805		__clocksource_suspend_select(cs);
 806	}
 807}
 808
 809/**
 810 * clocksource_start_suspend_timing - Start measuring the suspend timing
 811 * @cs:			current clocksource from timekeeping
 812 * @start_cycles:	current cycles from timekeeping
 813 *
 814 * This function will save the start cycle values of suspend timer to calculate
 815 * the suspend time when resuming system.
 816 *
 817 * This function is called late in the suspend process from timekeeping_suspend(),
 818 * that means processes are frozen, non-boot cpus and interrupts are disabled
 819 * now. It is therefore possible to start the suspend timer without taking the
 820 * clocksource mutex.
 821 */
 822void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles)
 823{
 824	if (!suspend_clocksource)
 825		return;
 826
 827	/*
 828	 * If current clocksource is the suspend timer, we should use the
 829	 * tkr_mono.cycle_last value as suspend_start to avoid same reading
 830	 * from suspend timer.
 831	 */
 832	if (clocksource_is_suspend(cs)) {
 833		suspend_start = start_cycles;
 834		return;
 835	}
 836
 837	if (suspend_clocksource->enable &&
 838	    suspend_clocksource->enable(suspend_clocksource)) {
 839		pr_warn_once("Failed to enable the non-suspend-able clocksource.\n");
 840		return;
 841	}
 842
 843	suspend_start = suspend_clocksource->read(suspend_clocksource);
 844}
 845
 846/**
 847 * clocksource_stop_suspend_timing - Stop measuring the suspend timing
 848 * @cs:		current clocksource from timekeeping
 849 * @cycle_now:	current cycles from timekeeping
 850 *
 851 * This function will calculate the suspend time from suspend timer.
 852 *
 853 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource.
 854 *
 855 * This function is called early in the resume process from timekeeping_resume(),
 856 * that means there is only one cpu, no processes are running and the interrupts
 857 * are disabled. It is therefore possible to stop the suspend timer without
 858 * taking the clocksource mutex.
 859 */
 860u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now)
 861{
 862	u64 now, nsec = 0;
 863
 864	if (!suspend_clocksource)
 865		return 0;
 866
 867	/*
 868	 * If current clocksource is the suspend timer, we should use the
 869	 * tkr_mono.cycle_last value from timekeeping as current cycle to
 870	 * avoid same reading from suspend timer.
 871	 */
 872	if (clocksource_is_suspend(cs))
 873		now = cycle_now;
 874	else
 875		now = suspend_clocksource->read(suspend_clocksource);
 876
 877	if (now > suspend_start)
 878		nsec = cycles_to_nsec_safe(suspend_clocksource, suspend_start, now);
 879
 880	/*
 881	 * Disable the suspend timer to save power if current clocksource is
 882	 * not the suspend timer.
 883	 */
 884	if (!clocksource_is_suspend(cs) && suspend_clocksource->disable)
 885		suspend_clocksource->disable(suspend_clocksource);
 886
 887	return nsec;
 888}
 889
 890/**
 891 * clocksource_suspend - suspend the clocksource(s)
 892 */
 893void clocksource_suspend(void)
 894{
 895	struct clocksource *cs;
 896
 897	list_for_each_entry_reverse(cs, &clocksource_list, list)
 898		if (cs->suspend)
 899			cs->suspend(cs);
 900}
 901
 902/**
 903 * clocksource_resume - resume the clocksource(s)
 904 */
 905void clocksource_resume(void)
 906{
 907	struct clocksource *cs;
 908
 909	list_for_each_entry(cs, &clocksource_list, list)
 910		if (cs->resume)
 911			cs->resume(cs);
 912
 913	clocksource_resume_watchdog();
 914}
 915
 916/**
 917 * clocksource_touch_watchdog - Update watchdog
 918 *
 919 * Update the watchdog after exception contexts such as kgdb so as not
 920 * to incorrectly trip the watchdog. This might fail when the kernel
 921 * was stopped in code which holds watchdog_lock.
 922 */
 923void clocksource_touch_watchdog(void)
 924{
 925	clocksource_resume_watchdog();
 926}
 927
 928/**
 929 * clocksource_max_adjustment- Returns max adjustment amount
 930 * @cs:         Pointer to clocksource
 931 *
 932 */
 933static u32 clocksource_max_adjustment(struct clocksource *cs)
 934{
 935	u64 ret;
 936	/*
 937	 * We won't try to correct for more than 11% adjustments (110,000 ppm),
 938	 */
 939	ret = (u64)cs->mult * 11;
 940	do_div(ret,100);
 941	return (u32)ret;
 942}
 943
 944/**
 945 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
 946 * @mult:	cycle to nanosecond multiplier
 947 * @shift:	cycle to nanosecond divisor (power of two)
 948 * @maxadj:	maximum adjustment value to mult (~11%)
 949 * @mask:	bitmask for two's complement subtraction of non 64 bit counters
 950 * @max_cyc:	maximum cycle value before potential overflow (does not include
 951 *		any safety margin)
 952 *
 953 * NOTE: This function includes a safety margin of 50%, in other words, we
 954 * return half the number of nanoseconds the hardware counter can technically
 955 * cover. This is done so that we can potentially detect problems caused by
 956 * delayed timers or bad hardware, which might result in time intervals that
 957 * are larger than what the math used can handle without overflows.
 958 */
 959u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)
 960{
 961	u64 max_nsecs, max_cycles;
 962
 963	/*
 964	 * Calculate the maximum number of cycles that we can pass to the
 965	 * cyc2ns() function without overflowing a 64-bit result.
 
 
 
 
 
 
 
 
 
 
 966	 */
 967	max_cycles = ULLONG_MAX;
 968	do_div(max_cycles, mult+maxadj);
 969
 970	/*
 971	 * The actual maximum number of cycles we can defer the clocksource is
 972	 * determined by the minimum of max_cycles and mask.
 973	 * Note: Here we subtract the maxadj to make sure we don't sleep for
 974	 * too long if there's a large negative adjustment.
 975	 */
 976	max_cycles = min(max_cycles, mask);
 977	max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
 978
 979	/* return the max_cycles value as well if requested */
 980	if (max_cyc)
 981		*max_cyc = max_cycles;
 982
 983	/* Return 50% of the actual maximum, so we can detect bad values */
 984	max_nsecs >>= 1;
 985
 986	return max_nsecs;
 987}
 988
 989/**
 990 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles
 991 * @cs:         Pointer to clocksource to be updated
 992 *
 993 */
 994static inline void clocksource_update_max_deferment(struct clocksource *cs)
 995{
 996	cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,
 997						cs->maxadj, cs->mask,
 998						&cs->max_cycles);
 999
1000	/*
1001	 * Threshold for detecting negative motion in clocksource_delta().
1002	 *
1003	 * Allow for 0.875 of the counter width so that overly long idle
1004	 * sleeps, which go slightly over mask/2, do not trigger the
1005	 * negative motion detection.
1006	 */
1007	cs->max_raw_delta = (cs->mask >> 1) + (cs->mask >> 2) + (cs->mask >> 3);
1008}
1009
1010static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
1011{
1012	struct clocksource *cs;
1013
1014	if (!finished_booting || list_empty(&clocksource_list))
1015		return NULL;
1016
1017	/*
1018	 * We pick the clocksource with the highest rating. If oneshot
1019	 * mode is active, we pick the highres valid clocksource with
1020	 * the best rating.
1021	 */
1022	list_for_each_entry(cs, &clocksource_list, list) {
1023		if (skipcur && cs == curr_clocksource)
1024			continue;
1025		if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1026			continue;
1027		return cs;
1028	}
1029	return NULL;
1030}
1031
1032static void __clocksource_select(bool skipcur)
 
 
 
 
 
 
 
 
1033{
1034	bool oneshot = tick_oneshot_mode_active();
1035	struct clocksource *best, *cs;
1036
1037	/* Find the best suitable clocksource */
1038	best = clocksource_find_best(oneshot, skipcur);
1039	if (!best)
1040		return;
1041
1042	if (!strlen(override_name))
1043		goto found;
1044
1045	/* Check for the override clocksource. */
1046	list_for_each_entry(cs, &clocksource_list, list) {
1047		if (skipcur && cs == curr_clocksource)
1048			continue;
1049		if (strcmp(cs->name, override_name) != 0)
1050			continue;
1051		/*
1052		 * Check to make sure we don't switch to a non-highres
1053		 * capable clocksource if the tick code is in oneshot
1054		 * mode (highres or nohz)
1055		 */
1056		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
 
1057			/* Override clocksource cannot be used. */
1058			if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
1059				pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n",
1060					cs->name);
1061				override_name[0] = 0;
1062			} else {
1063				/*
1064				 * The override cannot be currently verified.
1065				 * Deferring to let the watchdog check.
1066				 */
1067				pr_info("Override clocksource %s is not currently HRT compatible - deferring\n",
1068					cs->name);
1069			}
1070		} else
1071			/* Override clocksource can be used. */
1072			best = cs;
1073		break;
1074	}
1075
1076found:
1077	if (curr_clocksource != best && !timekeeping_notify(best)) {
1078		pr_info("Switched to clocksource %s\n", best->name);
1079		curr_clocksource = best;
 
1080	}
1081}
1082
1083/**
1084 * clocksource_select - Select the best clocksource available
1085 *
1086 * Private function. Must hold clocksource_mutex when called.
1087 *
1088 * Select the clocksource with the best rating, or the clocksource,
1089 * which is selected by userspace override.
1090 */
1091static void clocksource_select(void)
1092{
1093	__clocksource_select(false);
1094}
1095
1096static void clocksource_select_fallback(void)
1097{
1098	__clocksource_select(true);
1099}
1100
1101/*
1102 * clocksource_done_booting - Called near the end of core bootup
1103 *
1104 * Hack to avoid lots of clocksource churn at boot time.
1105 * We use fs_initcall because we want this to start before
1106 * device_initcall but after subsys_initcall.
1107 */
1108static int __init clocksource_done_booting(void)
1109{
1110	mutex_lock(&clocksource_mutex);
1111	curr_clocksource = clocksource_default_clock();
 
 
1112	finished_booting = 1;
 
1113	/*
1114	 * Run the watchdog first to eliminate unstable clock sources
1115	 */
1116	__clocksource_watchdog_kthread();
 
 
1117	clocksource_select();
1118	mutex_unlock(&clocksource_mutex);
1119	return 0;
1120}
1121fs_initcall(clocksource_done_booting);
1122
1123/*
1124 * Enqueue the clocksource sorted by rating
1125 */
1126static void clocksource_enqueue(struct clocksource *cs)
1127{
1128	struct list_head *entry = &clocksource_list;
1129	struct clocksource *tmp;
1130
1131	list_for_each_entry(tmp, &clocksource_list, list) {
1132		/* Keep track of the place, where to insert */
1133		if (tmp->rating < cs->rating)
1134			break;
1135		entry = &tmp->list;
1136	}
1137	list_add(&cs->list, entry);
1138}
1139
1140/**
1141 * __clocksource_update_freq_scale - Used update clocksource with new freq
1142 * @cs:		clocksource to be registered
1143 * @scale:	Scale factor multiplied against freq to get clocksource hz
1144 * @freq:	clocksource frequency (cycles per second) divided by scale
1145 *
1146 * This should only be called from the clocksource->enable() method.
1147 *
1148 * This *SHOULD NOT* be called directly! Please use the
1149 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper
1150 * functions.
1151 */
1152void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq)
1153{
1154	u64 sec;
1155
1156	/*
1157	 * Default clocksources are *special* and self-define their mult/shift.
1158	 * But, you're not special, so you should specify a freq value.
1159	 */
1160	if (freq) {
1161		/*
1162		 * Calc the maximum number of seconds which we can run before
1163		 * wrapping around. For clocksources which have a mask > 32-bit
1164		 * we need to limit the max sleep time to have a good
1165		 * conversion precision. 10 minutes is still a reasonable
1166		 * amount. That results in a shift value of 24 for a
1167		 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to
1168		 * ~ 0.06ppm granularity for NTP.
1169		 */
1170		sec = cs->mask;
1171		do_div(sec, freq);
1172		do_div(sec, scale);
1173		if (!sec)
1174			sec = 1;
1175		else if (sec > 600 && cs->mask > UINT_MAX)
1176			sec = 600;
1177
1178		clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
1179				       NSEC_PER_SEC / scale, sec * scale);
1180	}
1181
1182	/*
1183	 * If the uncertainty margin is not specified, calculate it.  If
1184	 * both scale and freq are non-zero, calculate the clock period, but
1185	 * bound below at 2*WATCHDOG_MAX_SKEW, that is, 500ppm by default.
1186	 * However, if either of scale or freq is zero, be very conservative
1187	 * and take the tens-of-milliseconds WATCHDOG_THRESHOLD value
1188	 * for the uncertainty margin.  Allow stupidly small uncertainty
1189	 * margins to be specified by the caller for testing purposes,
1190	 * but warn to discourage production use of this capability.
1191	 *
1192	 * Bottom line:  The sum of the uncertainty margins of the
1193	 * watchdog clocksource and the clocksource under test will be at
1194	 * least 500ppm by default.  For more information, please see the
1195	 * comment preceding CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US above.
1196	 */
1197	if (scale && freq && !cs->uncertainty_margin) {
1198		cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq);
1199		if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW)
1200			cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW;
1201	} else if (!cs->uncertainty_margin) {
1202		cs->uncertainty_margin = WATCHDOG_THRESHOLD;
1203	}
1204	WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW);
1205
1206	/*
1207	 * Ensure clocksources that have large 'mult' values don't overflow
1208	 * when adjusted.
1209	 */
1210	cs->maxadj = clocksource_max_adjustment(cs);
1211	while (freq && ((cs->mult + cs->maxadj < cs->mult)
1212		|| (cs->mult - cs->maxadj > cs->mult))) {
1213		cs->mult >>= 1;
1214		cs->shift--;
1215		cs->maxadj = clocksource_max_adjustment(cs);
1216	}
1217
1218	/*
1219	 * Only warn for *special* clocksources that self-define
1220	 * their mult/shift values and don't specify a freq.
1221	 */
1222	WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
1223		"timekeeping: Clocksource %s might overflow on 11%% adjustment\n",
1224		cs->name);
1225
1226	clocksource_update_max_deferment(cs);
1227
1228	pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n",
1229		cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns);
1230}
1231EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale);
1232
1233/**
1234 * __clocksource_register_scale - Used to install new clocksources
1235 * @cs:		clocksource to be registered
1236 * @scale:	Scale factor multiplied against freq to get clocksource hz
1237 * @freq:	clocksource frequency (cycles per second) divided by scale
1238 *
1239 * Returns -EBUSY if registration fails, zero otherwise.
1240 *
1241 * This *SHOULD NOT* be called directly! Please use the
1242 * clocksource_register_hz() or clocksource_register_khz helper functions.
1243 */
1244int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
1245{
1246	unsigned long flags;
1247
1248	clocksource_arch_init(cs);
1249
1250	if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX))
1251		cs->id = CSID_GENERIC;
1252	if (cs->vdso_clock_mode < 0 ||
1253	    cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) {
1254		pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n",
1255			cs->name, cs->vdso_clock_mode);
1256		cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
1257	}
1258
1259	/* Initialize mult/shift and max_idle_ns */
1260	__clocksource_update_freq_scale(cs, scale, freq);
1261
1262	/* Add clocksource to the clocksource list */
1263	mutex_lock(&clocksource_mutex);
1264
1265	clocksource_watchdog_lock(&flags);
1266	clocksource_enqueue(cs);
1267	clocksource_enqueue_watchdog(cs);
1268	clocksource_watchdog_unlock(&flags);
1269
1270	clocksource_select();
1271	clocksource_select_watchdog(false);
1272	__clocksource_suspend_select(cs);
1273	mutex_unlock(&clocksource_mutex);
1274	return 0;
1275}
1276EXPORT_SYMBOL_GPL(__clocksource_register_scale);
1277
1278/*
1279 * Unbind clocksource @cs. Called with clocksource_mutex held
 
 
 
 
1280 */
1281static int clocksource_unbind(struct clocksource *cs)
1282{
1283	unsigned long flags;
1284
1285	if (clocksource_is_watchdog(cs)) {
1286		/* Select and try to install a replacement watchdog. */
1287		clocksource_select_watchdog(true);
1288		if (clocksource_is_watchdog(cs))
1289			return -EBUSY;
1290	}
1291
1292	if (cs == curr_clocksource) {
1293		/* Select and try to install a replacement clock source */
1294		clocksource_select_fallback();
1295		if (curr_clocksource == cs)
1296			return -EBUSY;
1297	}
1298
1299	if (clocksource_is_suspend(cs)) {
1300		/*
1301		 * Select and try to install a replacement suspend clocksource.
1302		 * If no replacement suspend clocksource, we will just let the
1303		 * clocksource go and have no suspend clocksource.
1304		 */
1305		clocksource_suspend_select(true);
1306	}
1307
1308	clocksource_watchdog_lock(&flags);
1309	clocksource_dequeue_watchdog(cs);
1310	list_del_init(&cs->list);
1311	clocksource_watchdog_unlock(&flags);
 
 
 
1312
1313	return 0;
 
 
 
 
 
 
 
1314}
 
1315
1316/**
1317 * clocksource_unregister - remove a registered clocksource
1318 * @cs:	clocksource to be unregistered
1319 */
1320int clocksource_unregister(struct clocksource *cs)
1321{
1322	int ret = 0;
1323
1324	mutex_lock(&clocksource_mutex);
1325	if (!list_empty(&cs->list))
1326		ret = clocksource_unbind(cs);
 
1327	mutex_unlock(&clocksource_mutex);
1328	return ret;
1329}
1330EXPORT_SYMBOL(clocksource_unregister);
1331
1332#ifdef CONFIG_SYSFS
1333/**
1334 * current_clocksource_show - sysfs interface for current clocksource
1335 * @dev:	unused
1336 * @attr:	unused
1337 * @buf:	char buffer to be filled with clocksource list
1338 *
1339 * Provides sysfs interface for listing current clocksource.
1340 */
1341static ssize_t current_clocksource_show(struct device *dev,
1342					struct device_attribute *attr,
1343					char *buf)
1344{
1345	ssize_t count = 0;
1346
1347	mutex_lock(&clocksource_mutex);
1348	count = sysfs_emit(buf, "%s\n", curr_clocksource->name);
1349	mutex_unlock(&clocksource_mutex);
1350
1351	return count;
1352}
1353
1354ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
1355{
1356	size_t ret = cnt;
1357
1358	/* strings from sysfs write are not 0 terminated! */
1359	if (!cnt || cnt >= CS_NAME_LEN)
1360		return -EINVAL;
1361
1362	/* strip of \n: */
1363	if (buf[cnt-1] == '\n')
1364		cnt--;
1365	if (cnt > 0)
1366		memcpy(dst, buf, cnt);
1367	dst[cnt] = 0;
1368	return ret;
1369}
1370
1371/**
1372 * current_clocksource_store - interface for manually overriding clocksource
1373 * @dev:	unused
1374 * @attr:	unused
1375 * @buf:	name of override clocksource
1376 * @count:	length of buffer
1377 *
1378 * Takes input from sysfs interface for manually overriding the default
1379 * clocksource selection.
1380 */
1381static ssize_t current_clocksource_store(struct device *dev,
1382					 struct device_attribute *attr,
1383					 const char *buf, size_t count)
1384{
1385	ssize_t ret;
1386
1387	mutex_lock(&clocksource_mutex);
1388
1389	ret = sysfs_get_uname(buf, override_name, count);
1390	if (ret >= 0)
1391		clocksource_select();
1392
1393	mutex_unlock(&clocksource_mutex);
 
 
1394
1395	return ret;
1396}
1397static DEVICE_ATTR_RW(current_clocksource);
1398
1399/**
1400 * unbind_clocksource_store - interface for manually unbinding clocksource
1401 * @dev:	unused
1402 * @attr:	unused
1403 * @buf:	unused
1404 * @count:	length of buffer
1405 *
1406 * Takes input from sysfs interface for manually unbinding a clocksource.
1407 */
1408static ssize_t unbind_clocksource_store(struct device *dev,
1409					struct device_attribute *attr,
1410					const char *buf, size_t count)
1411{
1412	struct clocksource *cs;
1413	char name[CS_NAME_LEN];
1414	ssize_t ret;
1415
1416	ret = sysfs_get_uname(buf, name, count);
1417	if (ret < 0)
1418		return ret;
 
1419
1420	ret = -ENODEV;
1421	mutex_lock(&clocksource_mutex);
1422	list_for_each_entry(cs, &clocksource_list, list) {
1423		if (strcmp(cs->name, name))
1424			continue;
1425		ret = clocksource_unbind(cs);
1426		break;
1427	}
1428	mutex_unlock(&clocksource_mutex);
1429
1430	return ret ? ret : count;
1431}
1432static DEVICE_ATTR_WO(unbind_clocksource);
1433
1434/**
1435 * available_clocksource_show - sysfs interface for listing clocksource
1436 * @dev:	unused
1437 * @attr:	unused
1438 * @buf:	char buffer to be filled with clocksource list
1439 *
1440 * Provides sysfs interface for listing registered clocksources
1441 */
1442static ssize_t available_clocksource_show(struct device *dev,
1443					  struct device_attribute *attr,
1444					  char *buf)
 
1445{
1446	struct clocksource *src;
1447	ssize_t count = 0;
1448
1449	mutex_lock(&clocksource_mutex);
1450	list_for_each_entry(src, &clocksource_list, list) {
1451		/*
1452		 * Don't show non-HRES clocksource if the tick code is
1453		 * in one shot mode (highres=on or nohz=on)
1454		 */
1455		if (!tick_oneshot_mode_active() ||
1456		    (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1457			count += snprintf(buf + count,
1458				  max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1459				  "%s ", src->name);
1460	}
1461	mutex_unlock(&clocksource_mutex);
1462
1463	count += snprintf(buf + count,
1464			  max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1465
1466	return count;
1467}
1468static DEVICE_ATTR_RO(available_clocksource);
1469
1470static struct attribute *clocksource_attrs[] = {
1471	&dev_attr_current_clocksource.attr,
1472	&dev_attr_unbind_clocksource.attr,
1473	&dev_attr_available_clocksource.attr,
1474	NULL
1475};
1476ATTRIBUTE_GROUPS(clocksource);
 
1477
1478static const struct bus_type clocksource_subsys = {
1479	.name = "clocksource",
1480	.dev_name = "clocksource",
1481};
1482
1483static struct device device_clocksource = {
1484	.id	= 0,
1485	.bus	= &clocksource_subsys,
1486	.groups	= clocksource_groups,
1487};
1488
1489static int __init init_clocksource_sysfs(void)
1490{
1491	int error = subsys_system_register(&clocksource_subsys, NULL);
1492
1493	if (!error)
1494		error = device_register(&device_clocksource);
1495
 
 
 
 
 
 
 
1496	return error;
1497}
1498
1499device_initcall(init_clocksource_sysfs);
1500#endif /* CONFIG_SYSFS */
1501
1502/**
1503 * boot_override_clocksource - boot clock override
1504 * @str:	override name
1505 *
1506 * Takes a clocksource= boot argument and uses it
1507 * as the clocksource override name.
1508 */
1509static int __init boot_override_clocksource(char* str)
1510{
1511	mutex_lock(&clocksource_mutex);
1512	if (str)
1513		strscpy(override_name, str, sizeof(override_name));
1514	mutex_unlock(&clocksource_mutex);
1515	return 1;
1516}
1517
1518__setup("clocksource=", boot_override_clocksource);
1519
1520/**
1521 * boot_override_clock - Compatibility layer for deprecated boot option
1522 * @str:	override name
1523 *
1524 * DEPRECATED! Takes a clock= boot argument and uses it
1525 * as the clocksource override name
1526 */
1527static int __init boot_override_clock(char* str)
1528{
1529	if (!strcmp(str, "pmtmr")) {
1530		pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n");
 
1531		return boot_override_clocksource("acpi_pm");
1532	}
1533	pr_warn("clock= boot option is deprecated - use clocksource=xyz\n");
 
1534	return boot_override_clocksource(str);
1535}
1536
1537__setup("clock=", boot_override_clock);