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