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