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