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 EXPORT_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 */ 104 static struct clocksource *curr_clocksource; 105 static LIST_HEAD(clocksource_list); 106 static DEFINE_MUTEX(clocksource_mutex); 107 static char override_name[CS_NAME_LEN]; 108 static int finished_booting; 109 110 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG 111 static void clocksource_watchdog_work(struct work_struct *work); 112 static void clocksource_select(void); 113 114 static LIST_HEAD(watchdog_list); 115 static struct clocksource *watchdog; 116 static struct timer_list watchdog_timer; 117 static DECLARE_WORK(watchdog_work, clocksource_watchdog_work); 118 static DEFINE_SPINLOCK(watchdog_lock); 119 static int watchdog_running; 120 static atomic_t watchdog_reset_pending; 121 122 static int clocksource_watchdog_kthread(void *data); 123 static 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) 130 131 static 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 } 139 140 static 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 */ 157 void 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 } 169 170 static 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); 278 out: 279 spin_unlock(&watchdog_lock); 280 } 281 282 static 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 } 292 293 static 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 } 300 301 static 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 } 308 309 static void clocksource_resume_watchdog(void) 310 { 311 atomic_inc(&watchdog_reset_pending); 312 } 313 314 static 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 } 330 331 static 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 } 367 368 static 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 } 383 384 static 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 } 414 415 static 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 } 423 424 static bool clocksource_is_watchdog(struct clocksource *cs) 425 { 426 return cs == watchdog; 427 } 428 429 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */ 430 431 static 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 } 436 437 static void clocksource_select_watchdog(bool fallback) { } 438 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { } 439 static inline void clocksource_resume_watchdog(void) { } 440 static inline int __clocksource_watchdog_kthread(void) { return 0; } 441 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; } 442 void clocksource_mark_unstable(struct clocksource *cs) { } 443 444 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */ 445 446 /** 447 * clocksource_suspend - suspend the clocksource(s) 448 */ 449 void 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 */ 461 void 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 */ 479 void 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 */ 489 static 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 */ 515 u64 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 */ 550 static 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 558 559 static 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 } 580 581 static 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 */ 636 static void clocksource_select(void) 637 { 638 __clocksource_select(false); 639 } 640 641 static void clocksource_select_fallback(void) 642 { 643 __clocksource_select(true); 644 } 645 646 #else /* !CONFIG_ARCH_USES_GETTIMEOFFSET */ 647 static inline void clocksource_select(void) { } 648 static 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 */ 659 static 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 } 672 fs_initcall(clocksource_done_booting); 673 674 /* 675 * Enqueue the clocksource sorted by rating 676 */ 677 static 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 */ 703 void __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 } 757 EXPORT_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 */ 770 int __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 } 785 EXPORT_SYMBOL_GPL(__clocksource_register_scale); 786 787 static 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 */ 799 void 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 } 807 EXPORT_SYMBOL(clocksource_change_rating); 808 809 /* 810 * Unbind clocksource @cs. Called with clocksource_mutex held 811 */ 812 static 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 */ 836 int 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 } 846 EXPORT_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 */ 857 static ssize_t 858 sysfs_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 } 869 870 ssize_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 */ 897 static 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 */ 923 static 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 */ 956 static ssize_t 957 sysfs_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 */ 987 static DEVICE_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources, 988 sysfs_override_clocksource); 989 990 static DEVICE_ATTR(unbind_clocksource, 0200, NULL, sysfs_unbind_clocksource); 991 992 static DEVICE_ATTR(available_clocksource, 0444, 993 sysfs_show_available_clocksources, NULL); 994 995 static struct bus_type clocksource_subsys = { 996 .name = "clocksource", 997 .dev_name = "clocksource", 998 }; 999 1000 static struct device device_clocksource = { 1001 .id = 0, 1002 .bus = &clocksource_subsys, 1003 }; 1004 1005 static 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 1025 device_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 */ 1035 static 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 */ 1053 static 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); 1064