1/*
   2 * linux/kernel/time/clocksource.c
   3 *
   4 * This file contains the functions which manage clocksource drivers.
   5 *
   6 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
   7 *
   8 * This program is free software; you can redistribute it and/or modify
   9 * it under the terms of the GNU General Public License as published by
  10 * the Free Software Foundation; either version 2 of the License, or
  11 * (at your option) any later version.
  12 *
  13 * This program is distributed in the hope that it will be useful,
  14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 * GNU General Public License for more details.
  17 *
  18 * You should have received a copy of the GNU General Public License
  19 * along with this program; if not, write to the Free Software
  20 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  21 *
  22 * TODO WishList:
  23 *   o Allow clocksource drivers to be unregistered
  24 */
  25
  26#include <linux/device.h>
  27#include <linux/clocksource.h>
 
  28#include <linux/init.h>
  29#include <linux/module.h>
  30#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
  31#include <linux/tick.h>
  32#include <linux/kthread.h>
  33
  34#include "tick-internal.h"
  35
  36void timecounter_init(struct timecounter *tc,
  37		      const struct cyclecounter *cc,
  38		      u64 start_tstamp)
  39{
  40	tc->cc = cc;
  41	tc->cycle_last = cc->read(cc);
  42	tc->nsec = start_tstamp;
  43}
  44EXPORT_SYMBOL_GPL(timecounter_init);
  45
  46/**
  47 * timecounter_read_delta - get nanoseconds since last call of this function
  48 * @tc:         Pointer to time counter
  49 *
  50 * When the underlying cycle counter runs over, this will be handled
  51 * correctly as long as it does not run over more than once between
  52 * calls.
  53 *
  54 * The first call to this function for a new time counter initializes
  55 * the time tracking and returns an undefined result.
  56 */
  57static u64 timecounter_read_delta(struct timecounter *tc)
  58{
  59	cycle_t cycle_now, cycle_delta;
  60	u64 ns_offset;
  61
  62	/* read cycle counter: */
  63	cycle_now = tc->cc->read(tc->cc);
  64
  65	/* calculate the delta since the last timecounter_read_delta(): */
  66	cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
  67
  68	/* convert to nanoseconds: */
  69	ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta);
  70
  71	/* update time stamp of timecounter_read_delta() call: */
  72	tc->cycle_last = cycle_now;
  73
  74	return ns_offset;
  75}
  76
  77u64 timecounter_read(struct timecounter *tc)
  78{
  79	u64 nsec;
  80
  81	/* increment time by nanoseconds since last call */
  82	nsec = timecounter_read_delta(tc);
  83	nsec += tc->nsec;
  84	tc->nsec = nsec;
  85
  86	return nsec;
  87}
  88EXPORT_SYMBOL_GPL(timecounter_read);
  89
  90u64 timecounter_cyc2time(struct timecounter *tc,
  91			 cycle_t cycle_tstamp)
  92{
  93	u64 cycle_delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
  94	u64 nsec;
  95
  96	/*
  97	 * Instead of always treating cycle_tstamp as more recent
  98	 * than tc->cycle_last, detect when it is too far in the
  99	 * future and treat it as old time stamp instead.
 100	 */
 101	if (cycle_delta > tc->cc->mask / 2) {
 102		cycle_delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
 103		nsec = tc->nsec - cyclecounter_cyc2ns(tc->cc, cycle_delta);
 104	} else {
 105		nsec = cyclecounter_cyc2ns(tc->cc, cycle_delta) + tc->nsec;
 106	}
 107
 108	return nsec;
 109}
 110EXPORT_SYMBOL_GPL(timecounter_cyc2time);
 111
 112/**
 113 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
 114 * @mult:	pointer to mult variable
 115 * @shift:	pointer to shift variable
 116 * @from:	frequency to convert from
 117 * @to:		frequency to convert to
 118 * @maxsec:	guaranteed runtime conversion range in seconds
 119 *
 120 * The function evaluates the shift/mult pair for the scaled math
 121 * operations of clocksources and clockevents.
 122 *
 123 * @to and @from are frequency values in HZ. For clock sources @to is
 124 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
 125 * event @to is the counter frequency and @from is NSEC_PER_SEC.
 126 *
 127 * The @maxsec conversion range argument controls the time frame in
 128 * seconds which must be covered by the runtime conversion with the
 129 * calculated mult and shift factors. This guarantees that no 64bit
 130 * overflow happens when the input value of the conversion is
 131 * multiplied with the calculated mult factor. Larger ranges may
 132 * reduce the conversion accuracy by chosing smaller mult and shift
 133 * factors.
 134 */
 135void
 136clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec)
 137{
 138	u64 tmp;
 139	u32 sft, sftacc= 32;
 140
 141	/*
 142	 * Calculate the shift factor which is limiting the conversion
 143	 * range:
 144	 */
 145	tmp = ((u64)maxsec * from) >> 32;
 146	while (tmp) {
 147		tmp >>=1;
 148		sftacc--;
 149	}
 150
 151	/*
 152	 * Find the conversion shift/mult pair which has the best
 153	 * accuracy and fits the maxsec conversion range:
 154	 */
 155	for (sft = 32; sft > 0; sft--) {
 156		tmp = (u64) to << sft;
 157		tmp += from / 2;
 158		do_div(tmp, from);
 159		if ((tmp >> sftacc) == 0)
 160			break;
 161	}
 162	*mult = tmp;
 163	*shift = sft;
 164}
 165
 166/*[Clocksource internal variables]---------
 167 * curr_clocksource:
 168 *	currently selected clocksource.
 169 * clocksource_list:
 170 *	linked list with the registered clocksources
 171 * clocksource_mutex:
 172 *	protects manipulations to curr_clocksource and the clocksource_list
 173 * override_name:
 174 *	Name of the user-specified clocksource.
 175 */
 176static struct clocksource *curr_clocksource;
 177static LIST_HEAD(clocksource_list);
 178static DEFINE_MUTEX(clocksource_mutex);
 179static char override_name[CS_NAME_LEN];
 180static int finished_booting;
 181
 182#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
 183static void clocksource_watchdog_work(struct work_struct *work);
 184static void clocksource_select(void);
 185
 186static LIST_HEAD(watchdog_list);
 187static struct clocksource *watchdog;
 188static struct timer_list watchdog_timer;
 189static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
 190static DEFINE_SPINLOCK(watchdog_lock);
 191static int watchdog_running;
 192static atomic_t watchdog_reset_pending;
 193
 194static int clocksource_watchdog_kthread(void *data);
 195static void __clocksource_change_rating(struct clocksource *cs, int rating);
 196
 197/*
 198 * Interval: 0.5sec Threshold: 0.0625s
 199 */
 200#define WATCHDOG_INTERVAL (HZ >> 1)
 201#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
 202
 203static void clocksource_watchdog_work(struct work_struct *work)
 204{
 205	/*
 206	 * If kthread_run fails the next watchdog scan over the
 207	 * watchdog_list will find the unstable clock again.
 208	 */
 209	kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
 210}
 211
 212static void __clocksource_unstable(struct clocksource *cs)
 213{
 214	cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
 215	cs->flags |= CLOCK_SOURCE_UNSTABLE;
 216	if (finished_booting)
 217		schedule_work(&watchdog_work);
 218}
 219
 220static void clocksource_unstable(struct clocksource *cs, int64_t delta)
 221{
 222	printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
 223	       cs->name, delta);
 224	__clocksource_unstable(cs);
 225}
 226
 227/**
 228 * clocksource_mark_unstable - mark clocksource unstable via watchdog
 229 * @cs:		clocksource to be marked unstable
 230 *
 231 * This function is called instead of clocksource_change_rating from
 232 * cpu hotplug code to avoid a deadlock between the clocksource mutex
 233 * and the cpu hotplug mutex. It defers the update of the clocksource
 234 * to the watchdog thread.
 235 */
 236void clocksource_mark_unstable(struct clocksource *cs)
 237{
 238	unsigned long flags;
 239
 240	spin_lock_irqsave(&watchdog_lock, flags);
 241	if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
 242		if (list_empty(&cs->wd_list))
 243			list_add(&cs->wd_list, &watchdog_list);
 244		__clocksource_unstable(cs);
 245	}
 246	spin_unlock_irqrestore(&watchdog_lock, flags);
 247}
 248
 249static void clocksource_watchdog(unsigned long data)
 250{
 251	struct clocksource *cs;
 252	cycle_t csnow, wdnow;
 253	int64_t wd_nsec, cs_nsec;
 254	int next_cpu, reset_pending;
 255
 256	spin_lock(&watchdog_lock);
 257	if (!watchdog_running)
 258		goto out;
 259
 260	reset_pending = atomic_read(&watchdog_reset_pending);
 261
 262	list_for_each_entry(cs, &watchdog_list, wd_list) {
 263
 264		/* Clocksource already marked unstable? */
 265		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
 266			if (finished_booting)
 267				schedule_work(&watchdog_work);
 268			continue;
 269		}
 270
 271		local_irq_disable();
 272		csnow = cs->read(cs);
 273		wdnow = watchdog->read(watchdog);
 274		local_irq_enable();
 275
 276		/* Clocksource initialized ? */
 277		if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) ||
 278		    atomic_read(&watchdog_reset_pending)) {
 279			cs->flags |= CLOCK_SOURCE_WATCHDOG;
 280			cs->wd_last = wdnow;
 281			cs->cs_last = csnow;
 282			continue;
 283		}
 284
 285		wd_nsec = clocksource_cyc2ns((wdnow - cs->wd_last) & watchdog->mask,
 286					     watchdog->mult, watchdog->shift);
 287
 288		cs_nsec = clocksource_cyc2ns((csnow - cs->cs_last) &
 289					     cs->mask, cs->mult, cs->shift);
 290		cs->cs_last = csnow;
 291		cs->wd_last = wdnow;
 292
 293		if (atomic_read(&watchdog_reset_pending))
 294			continue;
 295
 296		/* Check the deviation from the watchdog clocksource. */
 297		if ((abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD)) {
 298			clocksource_unstable(cs, cs_nsec - wd_nsec);
 299			continue;
 300		}
 301
 302		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
 303		    (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
 304		    (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
 305			/* Mark it valid for high-res. */
 306			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 307
 308			/*
 309			 * clocksource_done_booting() will sort it if
 310			 * finished_booting is not set yet.
 
 311			 */
 312			if (!finished_booting)
 313				continue;
 314
 315			/*
 316			 * If this is not the current clocksource let
 317			 * the watchdog thread reselect it. Due to the
 318			 * change to high res this clocksource might
 319			 * be preferred now. If it is the current
 320			 * clocksource let the tick code know about
 321			 * that change.
 322			 */
 323			if (cs != curr_clocksource) {
 324				cs->flags |= CLOCK_SOURCE_RESELECT;
 325				schedule_work(&watchdog_work);
 326			} else {
 327				tick_clock_notify();
 328			}
 329		}
 330	}
 331
 332	/*
 333	 * We only clear the watchdog_reset_pending, when we did a
 334	 * full cycle through all clocksources.
 335	 */
 336	if (reset_pending)
 337		atomic_dec(&watchdog_reset_pending);
 338
 339	/*
 340	 * Cycle through CPUs to check if the CPUs stay synchronized
 341	 * to each other.
 342	 */
 343	next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
 344	if (next_cpu >= nr_cpu_ids)
 345		next_cpu = cpumask_first(cpu_online_mask);
 346	watchdog_timer.expires += WATCHDOG_INTERVAL;
 347	add_timer_on(&watchdog_timer, next_cpu);
 348out:
 349	spin_unlock(&watchdog_lock);
 350}
 351
 352static inline void clocksource_start_watchdog(void)
 353{
 354	if (watchdog_running || !watchdog || list_empty(&watchdog_list))
 355		return;
 356	init_timer(&watchdog_timer);
 357	watchdog_timer.function = clocksource_watchdog;
 358	watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
 359	add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
 360	watchdog_running = 1;
 361}
 362
 363static inline void clocksource_stop_watchdog(void)
 364{
 365	if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
 366		return;
 367	del_timer(&watchdog_timer);
 368	watchdog_running = 0;
 369}
 370
 371static inline void clocksource_reset_watchdog(void)
 372{
 373	struct clocksource *cs;
 374
 375	list_for_each_entry(cs, &watchdog_list, wd_list)
 376		cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
 377}
 378
 379static void clocksource_resume_watchdog(void)
 380{
 381	atomic_inc(&watchdog_reset_pending);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 382}
 383
 384static void clocksource_enqueue_watchdog(struct clocksource *cs)
 385{
 386	unsigned long flags;
 387
 388	spin_lock_irqsave(&watchdog_lock, flags);
 389	if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
 390		/* cs is a clocksource to be watched. */
 391		list_add(&cs->wd_list, &watchdog_list);
 392		cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
 393	} else {
 394		/* cs is a watchdog. */
 395		if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 396			cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 397		/* Pick the best watchdog. */
 398		if (!watchdog || cs->rating > watchdog->rating) {
 399			watchdog = cs;
 400			/* Reset watchdog cycles */
 401			clocksource_reset_watchdog();
 402		}
 403	}
 404	/* Check if the watchdog timer needs to be started. */
 405	clocksource_start_watchdog();
 406	spin_unlock_irqrestore(&watchdog_lock, flags);
 407}
 408
 409static void clocksource_dequeue_watchdog(struct clocksource *cs)
 410{
 
 411	unsigned long flags;
 412
 413	spin_lock_irqsave(&watchdog_lock, flags);
 414	if (cs != watchdog) {
 415		if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
 416			/* cs is a watched clocksource. */
 417			list_del_init(&cs->wd_list);
 418			/* Check if the watchdog timer needs to be stopped. */
 419			clocksource_stop_watchdog();
 
 
 
 
 
 
 
 420		}
 421	}
 
 
 
 422	spin_unlock_irqrestore(&watchdog_lock, flags);
 423}
 424
 425static int __clocksource_watchdog_kthread(void)
 426{
 427	struct clocksource *cs, *tmp;
 428	unsigned long flags;
 429	LIST_HEAD(unstable);
 430	int select = 0;
 431
 
 432	spin_lock_irqsave(&watchdog_lock, flags);
 433	list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
 434		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
 435			list_del_init(&cs->wd_list);
 436			list_add(&cs->wd_list, &unstable);
 437			select = 1;
 438		}
 439		if (cs->flags & CLOCK_SOURCE_RESELECT) {
 440			cs->flags &= ~CLOCK_SOURCE_RESELECT;
 441			select = 1;
 442		}
 443	}
 444	/* Check if the watchdog timer needs to be stopped. */
 445	clocksource_stop_watchdog();
 446	spin_unlock_irqrestore(&watchdog_lock, flags);
 447
 448	/* Needs to be done outside of watchdog lock */
 449	list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
 450		list_del_init(&cs->wd_list);
 451		__clocksource_change_rating(cs, 0);
 452	}
 453	return select;
 454}
 455
 456static int clocksource_watchdog_kthread(void *data)
 457{
 458	mutex_lock(&clocksource_mutex);
 459	if (__clocksource_watchdog_kthread())
 460		clocksource_select();
 461	mutex_unlock(&clocksource_mutex);
 462	return 0;
 463}
 464
 465static bool clocksource_is_watchdog(struct clocksource *cs)
 466{
 467	return cs == watchdog;
 468}
 469
 470#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
 471
 472static void clocksource_enqueue_watchdog(struct clocksource *cs)
 473{
 474	if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 475		cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 476}
 477
 478static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
 479static inline void clocksource_resume_watchdog(void) { }
 480static inline int __clocksource_watchdog_kthread(void) { return 0; }
 481static bool clocksource_is_watchdog(struct clocksource *cs) { return false; }
 482void clocksource_mark_unstable(struct clocksource *cs) { }
 483
 484#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
 485
 486/**
 487 * clocksource_suspend - suspend the clocksource(s)
 488 */
 489void clocksource_suspend(void)
 490{
 491	struct clocksource *cs;
 492
 493	list_for_each_entry_reverse(cs, &clocksource_list, list)
 494		if (cs->suspend)
 495			cs->suspend(cs);
 496}
 497
 498/**
 499 * clocksource_resume - resume the clocksource(s)
 500 */
 501void clocksource_resume(void)
 502{
 503	struct clocksource *cs;
 504
 505	list_for_each_entry(cs, &clocksource_list, list)
 506		if (cs->resume)
 507			cs->resume(cs);
 508
 509	clocksource_resume_watchdog();
 510}
 511
 512/**
 513 * clocksource_touch_watchdog - Update watchdog
 514 *
 515 * Update the watchdog after exception contexts such as kgdb so as not
 516 * to incorrectly trip the watchdog. This might fail when the kernel
 517 * was stopped in code which holds watchdog_lock.
 518 */
 519void clocksource_touch_watchdog(void)
 520{
 521	clocksource_resume_watchdog();
 522}
 523
 524/**
 525 * clocksource_max_adjustment- Returns max adjustment amount
 526 * @cs:         Pointer to clocksource
 527 *
 528 */
 529static u32 clocksource_max_adjustment(struct clocksource *cs)
 530{
 531	u64 ret;
 532	/*
 533	 * We won't try to correct for more than 11% adjustments (110,000 ppm),
 534	 */
 535	ret = (u64)cs->mult * 11;
 536	do_div(ret,100);
 537	return (u32)ret;
 538}
 539
 540/**
 541 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted
 542 * @mult:	cycle to nanosecond multiplier
 543 * @shift:	cycle to nanosecond divisor (power of two)
 544 * @maxadj:	maximum adjustment value to mult (~11%)
 545 * @mask:	bitmask for two's complement subtraction of non 64 bit counters
 546 */
 547u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask)
 548{
 549	u64 max_nsecs, max_cycles;
 550
 551	/*
 552	 * Calculate the maximum number of cycles that we can pass to the
 553	 * cyc2ns function without overflowing a 64-bit signed result. The
 554	 * maximum number of cycles is equal to ULLONG_MAX/(mult+maxadj)
 555	 * which is equivalent to the below.
 556	 * max_cycles < (2^63)/(mult + maxadj)
 557	 * max_cycles < 2^(log2((2^63)/(mult + maxadj)))
 558	 * max_cycles < 2^(log2(2^63) - log2(mult + maxadj))
 559	 * max_cycles < 2^(63 - log2(mult + maxadj))
 560	 * max_cycles < 1 << (63 - log2(mult + maxadj))
 561	 * Please note that we add 1 to the result of the log2 to account for
 562	 * any rounding errors, ensure the above inequality is satisfied and
 563	 * no overflow will occur.
 564	 */
 565	max_cycles = 1ULL << (63 - (ilog2(mult + maxadj) + 1));
 566
 567	/*
 568	 * The actual maximum number of cycles we can defer the clocksource is
 569	 * determined by the minimum of max_cycles and mask.
 570	 * Note: Here we subtract the maxadj to make sure we don't sleep for
 571	 * too long if there's a large negative adjustment.
 572	 */
 573	max_cycles = min(max_cycles, mask);
 574	max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);
 575
 576	return max_nsecs;
 577}
 578
 579/**
 580 * clocksource_max_deferment - Returns max time the clocksource can be deferred
 581 * @cs:         Pointer to clocksource
 582 *
 583 */
 584static u64 clocksource_max_deferment(struct clocksource *cs)
 585{
 586	u64 max_nsecs;
 587
 588	max_nsecs = clocks_calc_max_nsecs(cs->mult, cs->shift, cs->maxadj,
 589					  cs->mask);
 590	/*
 591	 * To ensure that the clocksource does not wrap whilst we are idle,
 592	 * limit the time the clocksource can be deferred by 12.5%. Please
 593	 * note a margin of 12.5% is used because this can be computed with
 594	 * a shift, versus say 10% which would require division.
 595	 */
 596	return max_nsecs - (max_nsecs >> 3);
 597}
 598
 599#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
 600
 601static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur)
 602{
 603	struct clocksource *cs;
 604
 605	if (!finished_booting || list_empty(&clocksource_list))
 606		return NULL;
 607
 608	/*
 609	 * We pick the clocksource with the highest rating. If oneshot
 610	 * mode is active, we pick the highres valid clocksource with
 611	 * the best rating.
 612	 */
 613	list_for_each_entry(cs, &clocksource_list, list) {
 614		if (skipcur && cs == curr_clocksource)
 615			continue;
 616		if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES))
 617			continue;
 618		return cs;
 619	}
 620	return NULL;
 621}
 622
 623static void __clocksource_select(bool skipcur)
 624{
 625	bool oneshot = tick_oneshot_mode_active();
 626	struct clocksource *best, *cs;
 627
 628	/* Find the best suitable clocksource */
 629	best = clocksource_find_best(oneshot, skipcur);
 630	if (!best)
 631		return;
 632
 
 633	/* Check for the override clocksource. */
 634	list_for_each_entry(cs, &clocksource_list, list) {
 635		if (skipcur && cs == curr_clocksource)
 636			continue;
 637		if (strcmp(cs->name, override_name) != 0)
 638			continue;
 639		/*
 640		 * Check to make sure we don't switch to a non-highres
 641		 * capable clocksource if the tick code is in oneshot
 642		 * mode (highres or nohz)
 643		 */
 644		if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) {
 
 645			/* Override clocksource cannot be used. */
 646			printk(KERN_WARNING "Override clocksource %s is not "
 647			       "HRT compatible. Cannot switch while in "
 648			       "HRT/NOHZ mode\n", cs->name);
 649			override_name[0] = 0;
 650		} else
 651			/* Override clocksource can be used. */
 652			best = cs;
 653		break;
 654	}
 655
 656	if (curr_clocksource != best && !timekeeping_notify(best)) {
 657		pr_info("Switched to clocksource %s\n", best->name);
 658		curr_clocksource = best;
 
 659	}
 660}
 661
 662/**
 663 * clocksource_select - Select the best clocksource available
 664 *
 665 * Private function. Must hold clocksource_mutex when called.
 666 *
 667 * Select the clocksource with the best rating, or the clocksource,
 668 * which is selected by userspace override.
 669 */
 670static void clocksource_select(void)
 671{
 672	return __clocksource_select(false);
 673}
 674
 675static void clocksource_select_fallback(void)
 676{
 677	return __clocksource_select(true);
 678}
 679
 680#else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */
 681
 682static inline void clocksource_select(void) { }
 683static inline void clocksource_select_fallback(void) { }
 684
 685#endif
 686
 687/*
 688 * clocksource_done_booting - Called near the end of core bootup
 689 *
 690 * Hack to avoid lots of clocksource churn at boot time.
 691 * We use fs_initcall because we want this to start before
 692 * device_initcall but after subsys_initcall.
 693 */
 694static int __init clocksource_done_booting(void)
 695{
 696	mutex_lock(&clocksource_mutex);
 697	curr_clocksource = clocksource_default_clock();
 
 
 698	finished_booting = 1;
 
 699	/*
 700	 * Run the watchdog first to eliminate unstable clock sources
 701	 */
 702	__clocksource_watchdog_kthread();
 
 
 703	clocksource_select();
 704	mutex_unlock(&clocksource_mutex);
 705	return 0;
 706}
 707fs_initcall(clocksource_done_booting);
 708
 709/*
 710 * Enqueue the clocksource sorted by rating
 711 */
 712static void clocksource_enqueue(struct clocksource *cs)
 713{
 714	struct list_head *entry = &clocksource_list;
 715	struct clocksource *tmp;
 716
 717	list_for_each_entry(tmp, &clocksource_list, list)
 718		/* Keep track of the place, where to insert */
 719		if (tmp->rating >= cs->rating)
 720			entry = &tmp->list;
 721	list_add(&cs->list, entry);
 722}
 723
 724/**
 725 * __clocksource_updatefreq_scale - Used update clocksource with new freq
 726 * @cs:		clocksource to be registered
 727 * @scale:	Scale factor multiplied against freq to get clocksource hz
 728 * @freq:	clocksource frequency (cycles per second) divided by scale
 729 *
 730 * This should only be called from the clocksource->enable() method.
 731 *
 732 * This *SHOULD NOT* be called directly! Please use the
 733 * clocksource_updatefreq_hz() or clocksource_updatefreq_khz helper functions.
 734 */
 735void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq)
 736{
 737	u64 sec;
 
 738	/*
 739	 * Calc the maximum number of seconds which we can run before
 740	 * wrapping around. For clocksources which have a mask > 32bit
 741	 * we need to limit the max sleep time to have a good
 742	 * conversion precision. 10 minutes is still a reasonable
 743	 * amount. That results in a shift value of 24 for a
 744	 * clocksource with mask >= 40bit and f >= 4GHz. That maps to
 745	 * ~ 0.06ppm granularity for NTP. We apply the same 12.5%
 746	 * margin as we do in clocksource_max_deferment()
 747	 */
 748	sec = (cs->mask - (cs->mask >> 3));
 749	do_div(sec, freq);
 750	do_div(sec, scale);
 751	if (!sec)
 752		sec = 1;
 753	else if (sec > 600 && cs->mask > UINT_MAX)
 754		sec = 600;
 755
 756	clocks_calc_mult_shift(&cs->mult, &cs->shift, freq,
 757			       NSEC_PER_SEC / scale, sec * scale);
 758
 759	/*
 760	 * for clocksources that have large mults, to avoid overflow.
 761	 * Since mult may be adjusted by ntp, add an safety extra margin
 762	 *
 763	 */
 764	cs->maxadj = clocksource_max_adjustment(cs);
 765	while ((cs->mult + cs->maxadj < cs->mult)
 766		|| (cs->mult - cs->maxadj > cs->mult)) {
 767		cs->mult >>= 1;
 768		cs->shift--;
 769		cs->maxadj = clocksource_max_adjustment(cs);
 770	}
 771
 772	cs->max_idle_ns = clocksource_max_deferment(cs);
 773}
 774EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);
 775
 776/**
 777 * __clocksource_register_scale - Used to install new clocksources
 778 * @cs:		clocksource to be registered
 779 * @scale:	Scale factor multiplied against freq to get clocksource hz
 780 * @freq:	clocksource frequency (cycles per second) divided by scale
 781 *
 782 * Returns -EBUSY if registration fails, zero otherwise.
 783 *
 784 * This *SHOULD NOT* be called directly! Please use the
 785 * clocksource_register_hz() or clocksource_register_khz helper functions.
 786 */
 787int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq)
 788{
 789
 790	/* Initialize mult/shift and max_idle_ns */
 791	__clocksource_updatefreq_scale(cs, scale, freq);
 792
 793	/* Add clocksource to the clcoksource list */
 794	mutex_lock(&clocksource_mutex);
 795	clocksource_enqueue(cs);
 796	clocksource_enqueue_watchdog(cs);
 797	clocksource_select();
 798	mutex_unlock(&clocksource_mutex);
 799	return 0;
 800}
 801EXPORT_SYMBOL_GPL(__clocksource_register_scale);
 802
 803
 804/**
 805 * clocksource_register - Used to install new clocksources
 806 * @cs:		clocksource to be registered
 807 *
 808 * Returns -EBUSY if registration fails, zero otherwise.
 809 */
 810int clocksource_register(struct clocksource *cs)
 811{
 812	/* calculate max adjustment for given mult/shift */
 813	cs->maxadj = clocksource_max_adjustment(cs);
 814	WARN_ONCE(cs->mult + cs->maxadj < cs->mult,
 815		"Clocksource %s might overflow on 11%% adjustment\n",
 816		cs->name);
 817
 818	/* calculate max idle time permitted for this clocksource */
 819	cs->max_idle_ns = clocksource_max_deferment(cs);
 820
 821	mutex_lock(&clocksource_mutex);
 822	clocksource_enqueue(cs);
 823	clocksource_enqueue_watchdog(cs);
 824	clocksource_select();
 825	mutex_unlock(&clocksource_mutex);
 826	return 0;
 827}
 828EXPORT_SYMBOL(clocksource_register);
 829
 830static void __clocksource_change_rating(struct clocksource *cs, int rating)
 831{
 832	list_del(&cs->list);
 833	cs->rating = rating;
 834	clocksource_enqueue(cs);
 
 835}
 836
 837/**
 838 * clocksource_change_rating - Change the rating of a registered clocksource
 839 * @cs:		clocksource to be changed
 840 * @rating:	new rating
 841 */
 842void clocksource_change_rating(struct clocksource *cs, int rating)
 843{
 844	mutex_lock(&clocksource_mutex);
 845	__clocksource_change_rating(cs, rating);
 846	clocksource_select();
 847	mutex_unlock(&clocksource_mutex);
 848}
 849EXPORT_SYMBOL(clocksource_change_rating);
 850
 851/*
 852 * Unbind clocksource @cs. Called with clocksource_mutex held
 853 */
 854static int clocksource_unbind(struct clocksource *cs)
 855{
 856	/*
 857	 * I really can't convince myself to support this on hardware
 858	 * designed by lobotomized monkeys.
 859	 */
 860	if (clocksource_is_watchdog(cs))
 861		return -EBUSY;
 862
 863	if (cs == curr_clocksource) {
 864		/* Select and try to install a replacement clock source */
 865		clocksource_select_fallback();
 866		if (curr_clocksource == cs)
 867			return -EBUSY;
 868	}
 869	clocksource_dequeue_watchdog(cs);
 870	list_del_init(&cs->list);
 871	return 0;
 872}
 873
 874/**
 875 * clocksource_unregister - remove a registered clocksource
 876 * @cs:	clocksource to be unregistered
 877 */
 878int clocksource_unregister(struct clocksource *cs)
 879{
 880	int ret = 0;
 881
 882	mutex_lock(&clocksource_mutex);
 883	if (!list_empty(&cs->list))
 884		ret = clocksource_unbind(cs);
 
 885	mutex_unlock(&clocksource_mutex);
 886	return ret;
 887}
 888EXPORT_SYMBOL(clocksource_unregister);
 889
 890#ifdef CONFIG_SYSFS
 891/**
 892 * sysfs_show_current_clocksources - sysfs interface for current clocksource
 893 * @dev:	unused
 894 * @attr:	unused
 895 * @buf:	char buffer to be filled with clocksource list
 896 *
 897 * Provides sysfs interface for listing current clocksource.
 898 */
 899static ssize_t
 900sysfs_show_current_clocksources(struct device *dev,
 901				struct device_attribute *attr, char *buf)
 902{
 903	ssize_t count = 0;
 904
 905	mutex_lock(&clocksource_mutex);
 906	count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
 907	mutex_unlock(&clocksource_mutex);
 908
 909	return count;
 910}
 911
 912ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt)
 913{
 914	size_t ret = cnt;
 915
 916	/* strings from sysfs write are not 0 terminated! */
 917	if (!cnt || cnt >= CS_NAME_LEN)
 918		return -EINVAL;
 919
 920	/* strip of \n: */
 921	if (buf[cnt-1] == '\n')
 922		cnt--;
 923	if (cnt > 0)
 924		memcpy(dst, buf, cnt);
 925	dst[cnt] = 0;
 926	return ret;
 927}
 928
 929/**
 930 * sysfs_override_clocksource - interface for manually overriding clocksource
 931 * @dev:	unused
 932 * @attr:	unused
 933 * @buf:	name of override clocksource
 934 * @count:	length of buffer
 935 *
 936 * Takes input from sysfs interface for manually overriding the default
 937 * clocksource selection.
 938 */
 939static ssize_t sysfs_override_clocksource(struct device *dev,
 940					  struct device_attribute *attr,
 941					  const char *buf, size_t count)
 942{
 943	ssize_t ret;
 944
 945	mutex_lock(&clocksource_mutex);
 946
 947	ret = sysfs_get_uname(buf, override_name, count);
 948	if (ret >= 0)
 949		clocksource_select();
 950
 951	mutex_unlock(&clocksource_mutex);
 
 
 952
 953	return ret;
 954}
 
 955
 956/**
 957 * sysfs_unbind_current_clocksource - interface for manually unbinding clocksource
 958 * @dev:	unused
 959 * @attr:	unused
 960 * @buf:	unused
 961 * @count:	length of buffer
 962 *
 963 * Takes input from sysfs interface for manually unbinding a clocksource.
 964 */
 965static ssize_t sysfs_unbind_clocksource(struct device *dev,
 966					struct device_attribute *attr,
 967					const char *buf, size_t count)
 968{
 969	struct clocksource *cs;
 970	char name[CS_NAME_LEN];
 971	ssize_t ret;
 972
 973	ret = sysfs_get_uname(buf, name, count);
 974	if (ret < 0)
 975		return ret;
 
 976
 977	ret = -ENODEV;
 978	mutex_lock(&clocksource_mutex);
 979	list_for_each_entry(cs, &clocksource_list, list) {
 980		if (strcmp(cs->name, name))
 981			continue;
 982		ret = clocksource_unbind(cs);
 983		break;
 984	}
 985	mutex_unlock(&clocksource_mutex);
 986
 987	return ret ? ret : count;
 988}
 989
 990/**
 991 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
 992 * @dev:	unused
 993 * @attr:	unused
 994 * @buf:	char buffer to be filled with clocksource list
 995 *
 996 * Provides sysfs interface for listing registered clocksources
 997 */
 998static ssize_t
 999sysfs_show_available_clocksources(struct device *dev,
1000				  struct device_attribute *attr,
1001				  char *buf)
1002{
1003	struct clocksource *src;
1004	ssize_t count = 0;
1005
1006	mutex_lock(&clocksource_mutex);
1007	list_for_each_entry(src, &clocksource_list, list) {
1008		/*
1009		 * Don't show non-HRES clocksource if the tick code is
1010		 * in one shot mode (highres=on or nohz=on)
1011		 */
1012		if (!tick_oneshot_mode_active() ||
1013		    (src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
1014			count += snprintf(buf + count,
1015				  max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
1016				  "%s ", src->name);
1017	}
1018	mutex_unlock(&clocksource_mutex);
1019
1020	count += snprintf(buf + count,
1021			  max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
1022
1023	return count;
1024}
1025
1026/*
1027 * Sysfs setup bits:
1028 */
1029static DEVICE_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
1030		   sysfs_override_clocksource);
1031
1032static DEVICE_ATTR(unbind_clocksource, 0200, NULL, sysfs_unbind_clocksource);
1033
1034static DEVICE_ATTR(available_clocksource, 0444,
1035		   sysfs_show_available_clocksources, NULL);
1036
1037static struct bus_type clocksource_subsys = {
1038	.name = "clocksource",
1039	.dev_name = "clocksource",
1040};
1041
1042static struct device device_clocksource = {
1043	.id	= 0,
1044	.bus	= &clocksource_subsys,
1045};
1046
1047static int __init init_clocksource_sysfs(void)
1048{
1049	int error = subsys_system_register(&clocksource_subsys, NULL);
1050
1051	if (!error)
1052		error = device_register(&device_clocksource);
1053	if (!error)
1054		error = device_create_file(
1055				&device_clocksource,
1056				&dev_attr_current_clocksource);
1057	if (!error)
1058		error = device_create_file(&device_clocksource,
1059					   &dev_attr_unbind_clocksource);
1060	if (!error)
1061		error = device_create_file(
1062				&device_clocksource,
1063				&dev_attr_available_clocksource);
1064	return error;
1065}
1066
1067device_initcall(init_clocksource_sysfs);
1068#endif /* CONFIG_SYSFS */
1069
1070/**
1071 * boot_override_clocksource - boot clock override
1072 * @str:	override name
1073 *
1074 * Takes a clocksource= boot argument and uses it
1075 * as the clocksource override name.
1076 */
1077static int __init boot_override_clocksource(char* str)
1078{
1079	mutex_lock(&clocksource_mutex);
1080	if (str)
1081		strlcpy(override_name, str, sizeof(override_name));
1082	mutex_unlock(&clocksource_mutex);
1083	return 1;
1084}
1085
1086__setup("clocksource=", boot_override_clocksource);
1087
1088/**
1089 * boot_override_clock - Compatibility layer for deprecated boot option
1090 * @str:	override name
1091 *
1092 * DEPRECATED! Takes a clock= boot argument and uses it
1093 * as the clocksource override name
1094 */
1095static int __init boot_override_clock(char* str)
1096{
1097	if (!strcmp(str, "pmtmr")) {
1098		printk("Warning: clock=pmtmr is deprecated. "
1099			"Use clocksource=acpi_pm.\n");
1100		return boot_override_clocksource("acpi_pm");
1101	}
1102	printk("Warning! clock= boot option is deprecated. "
1103		"Use clocksource=xyz\n");
1104	return boot_override_clocksource(str);
1105}
1106
1107__setup("clock=", boot_override_clock);