1 // SPDX-License-Identifier: GPL-2.0+ 2 /* 3 * This file contains the functions which manage clocksource drivers. 4 * 5 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com) 6 */ 7 8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 9 10 #include <linux/device.h> 11 #include <linux/clocksource.h> 12 #include <linux/init.h> 13 #include <linux/module.h> 14 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */ 15 #include <linux/tick.h> 16 #include <linux/kthread.h> 17 #include <linux/prandom.h> 18 #include <linux/cpu.h> 19 20 #include "tick-internal.h" 21 #include "timekeeping_internal.h" 22 23 /** 24 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks 25 * @mult: pointer to mult variable 26 * @shift: pointer to shift variable 27 * @from: frequency to convert from 28 * @to: frequency to convert to 29 * @maxsec: guaranteed runtime conversion range in seconds 30 * 31 * The function evaluates the shift/mult pair for the scaled math 32 * operations of clocksources and clockevents. 33 * 34 * @to and @from are frequency values in HZ. For clock sources @to is 35 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock 36 * event @to is the counter frequency and @from is NSEC_PER_SEC. 37 * 38 * The @maxsec conversion range argument controls the time frame in 39 * seconds which must be covered by the runtime conversion with the 40 * calculated mult and shift factors. This guarantees that no 64bit 41 * overflow happens when the input value of the conversion is 42 * multiplied with the calculated mult factor. Larger ranges may 43 * reduce the conversion accuracy by choosing smaller mult and shift 44 * factors. 45 */ 46 void 47 clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec) 48 { 49 u64 tmp; 50 u32 sft, sftacc= 32; 51 52 /* 53 * Calculate the shift factor which is limiting the conversion 54 * range: 55 */ 56 tmp = ((u64)maxsec * from) >> 32; 57 while (tmp) { 58 tmp >>=1; 59 sftacc--; 60 } 61 62 /* 63 * Find the conversion shift/mult pair which has the best 64 * accuracy and fits the maxsec conversion range: 65 */ 66 for (sft = 32; sft > 0; sft--) { 67 tmp = (u64) to << sft; 68 tmp += from / 2; 69 do_div(tmp, from); 70 if ((tmp >> sftacc) == 0) 71 break; 72 } 73 *mult = tmp; 74 *shift = sft; 75 } 76 EXPORT_SYMBOL_GPL(clocks_calc_mult_shift); 77 78 /*[Clocksource internal variables]--------- 79 * curr_clocksource: 80 * currently selected clocksource. 81 * suspend_clocksource: 82 * used to calculate the suspend time. 83 * clocksource_list: 84 * linked list with the registered clocksources 85 * clocksource_mutex: 86 * protects manipulations to curr_clocksource and the clocksource_list 87 * override_name: 88 * Name of the user-specified clocksource. 89 */ 90 static struct clocksource *curr_clocksource; 91 static struct clocksource *suspend_clocksource; 92 static LIST_HEAD(clocksource_list); 93 static DEFINE_MUTEX(clocksource_mutex); 94 static char override_name[CS_NAME_LEN]; 95 static int finished_booting; 96 static u64 suspend_start; 97 98 /* 99 * Interval: 0.5sec. 100 */ 101 #define WATCHDOG_INTERVAL (HZ >> 1) 102 #define WATCHDOG_INTERVAL_MAX_NS ((2 * WATCHDOG_INTERVAL) * (NSEC_PER_SEC / HZ)) 103 104 /* 105 * Threshold: 0.0312s, when doubled: 0.0625s. 106 * Also a default for cs->uncertainty_margin when registering clocks. 107 */ 108 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5) 109 110 /* 111 * Maximum permissible delay between two readouts of the watchdog 112 * clocksource surrounding a read of the clocksource being validated. 113 * This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as 114 * a lower bound for cs->uncertainty_margin values when registering clocks. 115 * 116 * The default of 500 parts per million is based on NTP's limits. 117 * If a clocksource is good enough for NTP, it is good enough for us! 118 */ 119 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 120 #define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 121 #else 122 #define MAX_SKEW_USEC (125 * WATCHDOG_INTERVAL / HZ) 123 #endif 124 125 #define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC) 126 127 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG 128 static void clocksource_watchdog_work(struct work_struct *work); 129 static void clocksource_select(void); 130 131 static LIST_HEAD(watchdog_list); 132 static struct clocksource *watchdog; 133 static struct timer_list watchdog_timer; 134 static DECLARE_WORK(watchdog_work, clocksource_watchdog_work); 135 static DEFINE_SPINLOCK(watchdog_lock); 136 static int watchdog_running; 137 static atomic_t watchdog_reset_pending; 138 static int64_t watchdog_max_interval; 139 140 static inline void clocksource_watchdog_lock(unsigned long *flags) 141 { 142 spin_lock_irqsave(&watchdog_lock, *flags); 143 } 144 145 static inline void clocksource_watchdog_unlock(unsigned long *flags) 146 { 147 spin_unlock_irqrestore(&watchdog_lock, *flags); 148 } 149 150 static int clocksource_watchdog_kthread(void *data); 151 static void __clocksource_change_rating(struct clocksource *cs, int rating); 152 153 static void clocksource_watchdog_work(struct work_struct *work) 154 { 155 /* 156 * We cannot directly run clocksource_watchdog_kthread() here, because 157 * clocksource_select() calls timekeeping_notify() which uses 158 * stop_machine(). One cannot use stop_machine() from a workqueue() due 159 * lock inversions wrt CPU hotplug. 160 * 161 * Also, we only ever run this work once or twice during the lifetime 162 * of the kernel, so there is no point in creating a more permanent 163 * kthread for this. 164 * 165 * If kthread_run fails the next watchdog scan over the 166 * watchdog_list will find the unstable clock again. 167 */ 168 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog"); 169 } 170 171 static void __clocksource_unstable(struct clocksource *cs) 172 { 173 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG); 174 cs->flags |= CLOCK_SOURCE_UNSTABLE; 175 176 /* 177 * If the clocksource is registered clocksource_watchdog_kthread() will 178 * re-rate and re-select. 179 */ 180 if (list_empty(&cs->list)) { 181 cs->rating = 0; 182 return; 183 } 184 185 if (cs->mark_unstable) 186 cs->mark_unstable(cs); 187 188 /* kick clocksource_watchdog_kthread() */ 189 if (finished_booting) 190 schedule_work(&watchdog_work); 191 } 192 193 /** 194 * clocksource_mark_unstable - mark clocksource unstable via watchdog 195 * @cs: clocksource to be marked unstable 196 * 197 * This function is called by the x86 TSC code to mark clocksources as unstable; 198 * it defers demotion and re-selection to a kthread. 199 */ 200 void clocksource_mark_unstable(struct clocksource *cs) 201 { 202 unsigned long flags; 203 204 spin_lock_irqsave(&watchdog_lock, flags); 205 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) { 206 if (!list_empty(&cs->list) && list_empty(&cs->wd_list)) 207 list_add(&cs->wd_list, &watchdog_list); 208 __clocksource_unstable(cs); 209 } 210 spin_unlock_irqrestore(&watchdog_lock, flags); 211 } 212 213 static int verify_n_cpus = 8; 214 module_param(verify_n_cpus, int, 0644); 215 216 enum wd_read_status { 217 WD_READ_SUCCESS, 218 WD_READ_UNSTABLE, 219 WD_READ_SKIP 220 }; 221 222 static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow) 223 { 224 unsigned int nretries, max_retries; 225 u64 wd_end, wd_end2, wd_delta; 226 int64_t wd_delay, wd_seq_delay; 227 228 max_retries = clocksource_get_max_watchdog_retry(); 229 for (nretries = 0; nretries <= max_retries; nretries++) { 230 local_irq_disable(); 231 *wdnow = watchdog->read(watchdog); 232 *csnow = cs->read(cs); 233 wd_end = watchdog->read(watchdog); 234 wd_end2 = watchdog->read(watchdog); 235 local_irq_enable(); 236 237 wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask); 238 wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, 239 watchdog->shift); 240 if (wd_delay <= WATCHDOG_MAX_SKEW) { 241 if (nretries > 1 || nretries >= max_retries) { 242 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n", 243 smp_processor_id(), watchdog->name, nretries); 244 } 245 return WD_READ_SUCCESS; 246 } 247 248 /* 249 * Now compute delay in consecutive watchdog read to see if 250 * there is too much external interferences that cause 251 * significant delay in reading both clocksource and watchdog. 252 * 253 * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2, 254 * report system busy, reinit the watchdog and skip the current 255 * watchdog test. 256 */ 257 wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask); 258 wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift); 259 if (wd_seq_delay > WATCHDOG_MAX_SKEW/2) 260 goto skip_test; 261 } 262 263 pr_warn("timekeeping watchdog on CPU%d: wd-%s-wd excessive read-back delay of %lldns vs. limit of %ldns, wd-wd read-back delay only %lldns, attempt %d, marking %s unstable\n", 264 smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name); 265 return WD_READ_UNSTABLE; 266 267 skip_test: 268 pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n", 269 smp_processor_id(), watchdog->name, wd_seq_delay); 270 pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n", 271 cs->name, wd_delay); 272 return WD_READ_SKIP; 273 } 274 275 static u64 csnow_mid; 276 static cpumask_t cpus_ahead; 277 static cpumask_t cpus_behind; 278 static cpumask_t cpus_chosen; 279 280 static void clocksource_verify_choose_cpus(void) 281 { 282 int cpu, i, n = verify_n_cpus; 283 284 if (n < 0) { 285 /* Check all of the CPUs. */ 286 cpumask_copy(&cpus_chosen, cpu_online_mask); 287 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); 288 return; 289 } 290 291 /* If no checking desired, or no other CPU to check, leave. */ 292 cpumask_clear(&cpus_chosen); 293 if (n == 0 || num_online_cpus() <= 1) 294 return; 295 296 /* Make sure to select at least one CPU other than the current CPU. */ 297 cpu = cpumask_first(cpu_online_mask); 298 if (cpu == smp_processor_id()) 299 cpu = cpumask_next(cpu, cpu_online_mask); 300 if (WARN_ON_ONCE(cpu >= nr_cpu_ids)) 301 return; 302 cpumask_set_cpu(cpu, &cpus_chosen); 303 304 /* Force a sane value for the boot parameter. */ 305 if (n > nr_cpu_ids) 306 n = nr_cpu_ids; 307 308 /* 309 * Randomly select the specified number of CPUs. If the same 310 * CPU is selected multiple times, that CPU is checked only once, 311 * and no replacement CPU is selected. This gracefully handles 312 * situations where verify_n_cpus is greater than the number of 313 * CPUs that are currently online. 314 */ 315 for (i = 1; i < n; i++) { 316 cpu = get_random_u32_below(nr_cpu_ids); 317 cpu = cpumask_next(cpu - 1, cpu_online_mask); 318 if (cpu >= nr_cpu_ids) 319 cpu = cpumask_first(cpu_online_mask); 320 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids)) 321 cpumask_set_cpu(cpu, &cpus_chosen); 322 } 323 324 /* Don't verify ourselves. */ 325 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); 326 } 327 328 static void clocksource_verify_one_cpu(void *csin) 329 { 330 struct clocksource *cs = (struct clocksource *)csin; 331 332 csnow_mid = cs->read(cs); 333 } 334 335 void clocksource_verify_percpu(struct clocksource *cs) 336 { 337 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX; 338 u64 csnow_begin, csnow_end; 339 int cpu, testcpu; 340 s64 delta; 341 342 if (verify_n_cpus == 0) 343 return; 344 cpumask_clear(&cpus_ahead); 345 cpumask_clear(&cpus_behind); 346 cpus_read_lock(); 347 preempt_disable(); 348 clocksource_verify_choose_cpus(); 349 if (cpumask_empty(&cpus_chosen)) { 350 preempt_enable(); 351 cpus_read_unlock(); 352 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name); 353 return; 354 } 355 testcpu = smp_processor_id(); 356 pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen)); 357 for_each_cpu(cpu, &cpus_chosen) { 358 if (cpu == testcpu) 359 continue; 360 csnow_begin = cs->read(cs); 361 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1); 362 csnow_end = cs->read(cs); 363 delta = (s64)((csnow_mid - csnow_begin) & cs->mask); 364 if (delta < 0) 365 cpumask_set_cpu(cpu, &cpus_behind); 366 delta = (csnow_end - csnow_mid) & cs->mask; 367 if (delta < 0) 368 cpumask_set_cpu(cpu, &cpus_ahead); 369 delta = clocksource_delta(csnow_end, csnow_begin, cs->mask); 370 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift); 371 if (cs_nsec > cs_nsec_max) 372 cs_nsec_max = cs_nsec; 373 if (cs_nsec < cs_nsec_min) 374 cs_nsec_min = cs_nsec; 375 } 376 preempt_enable(); 377 cpus_read_unlock(); 378 if (!cpumask_empty(&cpus_ahead)) 379 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n", 380 cpumask_pr_args(&cpus_ahead), testcpu, cs->name); 381 if (!cpumask_empty(&cpus_behind)) 382 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n", 383 cpumask_pr_args(&cpus_behind), testcpu, cs->name); 384 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind)) 385 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n", 386 testcpu, cs_nsec_min, cs_nsec_max, cs->name); 387 } 388 EXPORT_SYMBOL_GPL(clocksource_verify_percpu); 389 390 static inline void clocksource_reset_watchdog(void) 391 { 392 struct clocksource *cs; 393 394 list_for_each_entry(cs, &watchdog_list, wd_list) 395 cs->flags &= ~CLOCK_SOURCE_WATCHDOG; 396 } 397 398 399 static void clocksource_watchdog(struct timer_list *unused) 400 { 401 u64 csnow, wdnow, cslast, wdlast, delta; 402 int64_t wd_nsec, cs_nsec, interval; 403 int next_cpu, reset_pending; 404 struct clocksource *cs; 405 enum wd_read_status read_ret; 406 unsigned long extra_wait = 0; 407 u32 md; 408 409 spin_lock(&watchdog_lock); 410 if (!watchdog_running) 411 goto out; 412 413 reset_pending = atomic_read(&watchdog_reset_pending); 414 415 list_for_each_entry(cs, &watchdog_list, wd_list) { 416 417 /* Clocksource already marked unstable? */ 418 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 419 if (finished_booting) 420 schedule_work(&watchdog_work); 421 continue; 422 } 423 424 read_ret = cs_watchdog_read(cs, &csnow, &wdnow); 425 426 if (read_ret == WD_READ_UNSTABLE) { 427 /* Clock readout unreliable, so give it up. */ 428 __clocksource_unstable(cs); 429 continue; 430 } 431 432 /* 433 * When WD_READ_SKIP is returned, it means the system is likely 434 * under very heavy load, where the latency of reading 435 * watchdog/clocksource is very big, and affect the accuracy of 436 * watchdog check. So give system some space and suspend the 437 * watchdog check for 5 minutes. 438 */ 439 if (read_ret == WD_READ_SKIP) { 440 /* 441 * As the watchdog timer will be suspended, and 442 * cs->last could keep unchanged for 5 minutes, reset 443 * the counters. 444 */ 445 clocksource_reset_watchdog(); 446 extra_wait = HZ * 300; 447 break; 448 } 449 450 /* Clocksource initialized ? */ 451 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) || 452 atomic_read(&watchdog_reset_pending)) { 453 cs->flags |= CLOCK_SOURCE_WATCHDOG; 454 cs->wd_last = wdnow; 455 cs->cs_last = csnow; 456 continue; 457 } 458 459 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask); 460 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult, 461 watchdog->shift); 462 463 delta = clocksource_delta(csnow, cs->cs_last, cs->mask); 464 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift); 465 wdlast = cs->wd_last; /* save these in case we print them */ 466 cslast = cs->cs_last; 467 cs->cs_last = csnow; 468 cs->wd_last = wdnow; 469 470 if (atomic_read(&watchdog_reset_pending)) 471 continue; 472 473 /* 474 * The processing of timer softirqs can get delayed (usually 475 * on account of ksoftirqd not getting to run in a timely 476 * manner), which causes the watchdog interval to stretch. 477 * Skew detection may fail for longer watchdog intervals 478 * on account of fixed margins being used. 479 * Some clocksources, e.g. acpi_pm, cannot tolerate 480 * watchdog intervals longer than a few seconds. 481 */ 482 interval = max(cs_nsec, wd_nsec); 483 if (unlikely(interval > WATCHDOG_INTERVAL_MAX_NS)) { 484 if (system_state > SYSTEM_SCHEDULING && 485 interval > 2 * watchdog_max_interval) { 486 watchdog_max_interval = interval; 487 pr_warn("Long readout interval, skipping watchdog check: cs_nsec: %lld wd_nsec: %lld\n", 488 cs_nsec, wd_nsec); 489 } 490 watchdog_timer.expires = jiffies; 491 continue; 492 } 493 494 /* Check the deviation from the watchdog clocksource. */ 495 md = cs->uncertainty_margin + watchdog->uncertainty_margin; 496 if (abs(cs_nsec - wd_nsec) > md) { 497 s64 cs_wd_msec; 498 s64 wd_msec; 499 u32 wd_rem; 500 501 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n", 502 smp_processor_id(), cs->name); 503 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n", 504 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask); 505 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n", 506 cs->name, cs_nsec, csnow, cslast, cs->mask); 507 cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem); 508 wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem); 509 pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n", 510 cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec); 511 if (curr_clocksource == cs) 512 pr_warn(" '%s' is current clocksource.\n", cs->name); 513 else if (curr_clocksource) 514 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name); 515 else 516 pr_warn(" No current clocksource.\n"); 517 __clocksource_unstable(cs); 518 continue; 519 } 520 521 if (cs == curr_clocksource && cs->tick_stable) 522 cs->tick_stable(cs); 523 524 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && 525 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) && 526 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) { 527 /* Mark it valid for high-res. */ 528 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 529 530 /* 531 * clocksource_done_booting() will sort it if 532 * finished_booting is not set yet. 533 */ 534 if (!finished_booting) 535 continue; 536 537 /* 538 * If this is not the current clocksource let 539 * the watchdog thread reselect it. Due to the 540 * change to high res this clocksource might 541 * be preferred now. If it is the current 542 * clocksource let the tick code know about 543 * that change. 544 */ 545 if (cs != curr_clocksource) { 546 cs->flags |= CLOCK_SOURCE_RESELECT; 547 schedule_work(&watchdog_work); 548 } else { 549 tick_clock_notify(); 550 } 551 } 552 } 553 554 /* 555 * We only clear the watchdog_reset_pending, when we did a 556 * full cycle through all clocksources. 557 */ 558 if (reset_pending) 559 atomic_dec(&watchdog_reset_pending); 560 561 /* 562 * Cycle through CPUs to check if the CPUs stay synchronized 563 * to each other. 564 */ 565 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask); 566 if (next_cpu >= nr_cpu_ids) 567 next_cpu = cpumask_first(cpu_online_mask); 568 569 /* 570 * Arm timer if not already pending: could race with concurrent 571 * pair clocksource_stop_watchdog() clocksource_start_watchdog(). 572 */ 573 if (!timer_pending(&watchdog_timer)) { 574 watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait; 575 add_timer_on(&watchdog_timer, next_cpu); 576 } 577 out: 578 spin_unlock(&watchdog_lock); 579 } 580 581 static inline void clocksource_start_watchdog(void) 582 { 583 if (watchdog_running || !watchdog || list_empty(&watchdog_list)) 584 return; 585 timer_setup(&watchdog_timer, clocksource_watchdog, 0); 586 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL; 587 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask)); 588 watchdog_running = 1; 589 } 590 591 static inline void clocksource_stop_watchdog(void) 592 { 593 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list))) 594 return; 595 del_timer(&watchdog_timer); 596 watchdog_running = 0; 597 } 598 599 static void clocksource_resume_watchdog(void) 600 { 601 atomic_inc(&watchdog_reset_pending); 602 } 603 604 static void clocksource_enqueue_watchdog(struct clocksource *cs) 605 { 606 INIT_LIST_HEAD(&cs->wd_list); 607 608 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { 609 /* cs is a clocksource to be watched. */ 610 list_add(&cs->wd_list, &watchdog_list); 611 cs->flags &= ~CLOCK_SOURCE_WATCHDOG; 612 } else { 613 /* cs is a watchdog. */ 614 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 615 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 616 } 617 } 618 619 static void clocksource_select_watchdog(bool fallback) 620 { 621 struct clocksource *cs, *old_wd; 622 unsigned long flags; 623 624 spin_lock_irqsave(&watchdog_lock, flags); 625 /* save current watchdog */ 626 old_wd = watchdog; 627 if (fallback) 628 watchdog = NULL; 629 630 list_for_each_entry(cs, &clocksource_list, list) { 631 /* cs is a clocksource to be watched. */ 632 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) 633 continue; 634 635 /* Skip current if we were requested for a fallback. */ 636 if (fallback && cs == old_wd) 637 continue; 638 639 /* Pick the best watchdog. */ 640 if (!watchdog || cs->rating > watchdog->rating) 641 watchdog = cs; 642 } 643 /* If we failed to find a fallback restore the old one. */ 644 if (!watchdog) 645 watchdog = old_wd; 646 647 /* If we changed the watchdog we need to reset cycles. */ 648 if (watchdog != old_wd) 649 clocksource_reset_watchdog(); 650 651 /* Check if the watchdog timer needs to be started. */ 652 clocksource_start_watchdog(); 653 spin_unlock_irqrestore(&watchdog_lock, flags); 654 } 655 656 static void clocksource_dequeue_watchdog(struct clocksource *cs) 657 { 658 if (cs != watchdog) { 659 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { 660 /* cs is a watched clocksource. */ 661 list_del_init(&cs->wd_list); 662 /* Check if the watchdog timer needs to be stopped. */ 663 clocksource_stop_watchdog(); 664 } 665 } 666 } 667 668 static int __clocksource_watchdog_kthread(void) 669 { 670 struct clocksource *cs, *tmp; 671 unsigned long flags; 672 int select = 0; 673 674 /* Do any required per-CPU skew verification. */ 675 if (curr_clocksource && 676 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE && 677 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU) 678 clocksource_verify_percpu(curr_clocksource); 679 680 spin_lock_irqsave(&watchdog_lock, flags); 681 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) { 682 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 683 list_del_init(&cs->wd_list); 684 __clocksource_change_rating(cs, 0); 685 select = 1; 686 } 687 if (cs->flags & CLOCK_SOURCE_RESELECT) { 688 cs->flags &= ~CLOCK_SOURCE_RESELECT; 689 select = 1; 690 } 691 } 692 /* Check if the watchdog timer needs to be stopped. */ 693 clocksource_stop_watchdog(); 694 spin_unlock_irqrestore(&watchdog_lock, flags); 695 696 return select; 697 } 698 699 static int clocksource_watchdog_kthread(void *data) 700 { 701 mutex_lock(&clocksource_mutex); 702 if (__clocksource_watchdog_kthread()) 703 clocksource_select(); 704 mutex_unlock(&clocksource_mutex); 705 return 0; 706 } 707 708 static bool clocksource_is_watchdog(struct clocksource *cs) 709 { 710 return cs == watchdog; 711 } 712 713 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */ 714 715 static void clocksource_enqueue_watchdog(struct clocksource *cs) 716 { 717 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 718 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 719 } 720 721 static void clocksource_select_watchdog(bool fallback) { } 722 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { } 723 static inline void clocksource_resume_watchdog(void) { } 724 static inline int __clocksource_watchdog_kthread(void) { return 0; } 725 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; } 726 void clocksource_mark_unstable(struct clocksource *cs) { } 727 728 static inline void clocksource_watchdog_lock(unsigned long *flags) { } 729 static inline void clocksource_watchdog_unlock(unsigned long *flags) { } 730 731 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */ 732 733 static bool clocksource_is_suspend(struct clocksource *cs) 734 { 735 return cs == suspend_clocksource; 736 } 737 738 static void __clocksource_suspend_select(struct clocksource *cs) 739 { 740 /* 741 * Skip the clocksource which will be stopped in suspend state. 742 */ 743 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP)) 744 return; 745 746 /* 747 * The nonstop clocksource can be selected as the suspend clocksource to 748 * calculate the suspend time, so it should not supply suspend/resume 749 * interfaces to suspend the nonstop clocksource when system suspends. 750 */ 751 if (cs->suspend || cs->resume) { 752 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n", 753 cs->name); 754 } 755 756 /* Pick the best rating. */ 757 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating) 758 suspend_clocksource = cs; 759 } 760 761 /** 762 * clocksource_suspend_select - Select the best clocksource for suspend timing 763 * @fallback: if select a fallback clocksource 764 */ 765 static void clocksource_suspend_select(bool fallback) 766 { 767 struct clocksource *cs, *old_suspend; 768 769 old_suspend = suspend_clocksource; 770 if (fallback) 771 suspend_clocksource = NULL; 772 773 list_for_each_entry(cs, &clocksource_list, list) { 774 /* Skip current if we were requested for a fallback. */ 775 if (fallback && cs == old_suspend) 776 continue; 777 778 __clocksource_suspend_select(cs); 779 } 780 } 781 782 /** 783 * clocksource_start_suspend_timing - Start measuring the suspend timing 784 * @cs: current clocksource from timekeeping 785 * @start_cycles: current cycles from timekeeping 786 * 787 * This function will save the start cycle values of suspend timer to calculate 788 * the suspend time when resuming system. 789 * 790 * This function is called late in the suspend process from timekeeping_suspend(), 791 * that means processes are frozen, non-boot cpus and interrupts are disabled 792 * now. It is therefore possible to start the suspend timer without taking the 793 * clocksource mutex. 794 */ 795 void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles) 796 { 797 if (!suspend_clocksource) 798 return; 799 800 /* 801 * If current clocksource is the suspend timer, we should use the 802 * tkr_mono.cycle_last value as suspend_start to avoid same reading 803 * from suspend timer. 804 */ 805 if (clocksource_is_suspend(cs)) { 806 suspend_start = start_cycles; 807 return; 808 } 809 810 if (suspend_clocksource->enable && 811 suspend_clocksource->enable(suspend_clocksource)) { 812 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n"); 813 return; 814 } 815 816 suspend_start = suspend_clocksource->read(suspend_clocksource); 817 } 818 819 /** 820 * clocksource_stop_suspend_timing - Stop measuring the suspend timing 821 * @cs: current clocksource from timekeeping 822 * @cycle_now: current cycles from timekeeping 823 * 824 * This function will calculate the suspend time from suspend timer. 825 * 826 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource. 827 * 828 * This function is called early in the resume process from timekeeping_resume(), 829 * that means there is only one cpu, no processes are running and the interrupts 830 * are disabled. It is therefore possible to stop the suspend timer without 831 * taking the clocksource mutex. 832 */ 833 u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now) 834 { 835 u64 now, delta, nsec = 0; 836 837 if (!suspend_clocksource) 838 return 0; 839 840 /* 841 * If current clocksource is the suspend timer, we should use the 842 * tkr_mono.cycle_last value from timekeeping as current cycle to 843 * avoid same reading from suspend timer. 844 */ 845 if (clocksource_is_suspend(cs)) 846 now = cycle_now; 847 else 848 now = suspend_clocksource->read(suspend_clocksource); 849 850 if (now > suspend_start) { 851 delta = clocksource_delta(now, suspend_start, 852 suspend_clocksource->mask); 853 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult, 854 suspend_clocksource->shift); 855 } 856 857 /* 858 * Disable the suspend timer to save power if current clocksource is 859 * not the suspend timer. 860 */ 861 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable) 862 suspend_clocksource->disable(suspend_clocksource); 863 864 return nsec; 865 } 866 867 /** 868 * clocksource_suspend - suspend the clocksource(s) 869 */ 870 void clocksource_suspend(void) 871 { 872 struct clocksource *cs; 873 874 list_for_each_entry_reverse(cs, &clocksource_list, list) 875 if (cs->suspend) 876 cs->suspend(cs); 877 } 878 879 /** 880 * clocksource_resume - resume the clocksource(s) 881 */ 882 void clocksource_resume(void) 883 { 884 struct clocksource *cs; 885 886 list_for_each_entry(cs, &clocksource_list, list) 887 if (cs->resume) 888 cs->resume(cs); 889 890 clocksource_resume_watchdog(); 891 } 892 893 /** 894 * clocksource_touch_watchdog - Update watchdog 895 * 896 * Update the watchdog after exception contexts such as kgdb so as not 897 * to incorrectly trip the watchdog. This might fail when the kernel 898 * was stopped in code which holds watchdog_lock. 899 */ 900 void clocksource_touch_watchdog(void) 901 { 902 clocksource_resume_watchdog(); 903 } 904 905 /** 906 * clocksource_max_adjustment- Returns max adjustment amount 907 * @cs: Pointer to clocksource 908 * 909 */ 910 static u32 clocksource_max_adjustment(struct clocksource *cs) 911 { 912 u64 ret; 913 /* 914 * We won't try to correct for more than 11% adjustments (110,000 ppm), 915 */ 916 ret = (u64)cs->mult * 11; 917 do_div(ret,100); 918 return (u32)ret; 919 } 920 921 /** 922 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted 923 * @mult: cycle to nanosecond multiplier 924 * @shift: cycle to nanosecond divisor (power of two) 925 * @maxadj: maximum adjustment value to mult (~11%) 926 * @mask: bitmask for two's complement subtraction of non 64 bit counters 927 * @max_cyc: maximum cycle value before potential overflow (does not include 928 * any safety margin) 929 * 930 * NOTE: This function includes a safety margin of 50%, in other words, we 931 * return half the number of nanoseconds the hardware counter can technically 932 * cover. This is done so that we can potentially detect problems caused by 933 * delayed timers or bad hardware, which might result in time intervals that 934 * are larger than what the math used can handle without overflows. 935 */ 936 u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc) 937 { 938 u64 max_nsecs, max_cycles; 939 940 /* 941 * Calculate the maximum number of cycles that we can pass to the 942 * cyc2ns() function without overflowing a 64-bit result. 943 */ 944 max_cycles = ULLONG_MAX; 945 do_div(max_cycles, mult+maxadj); 946 947 /* 948 * The actual maximum number of cycles we can defer the clocksource is 949 * determined by the minimum of max_cycles and mask. 950 * Note: Here we subtract the maxadj to make sure we don't sleep for 951 * too long if there's a large negative adjustment. 952 */ 953 max_cycles = min(max_cycles, mask); 954 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift); 955 956 /* return the max_cycles value as well if requested */ 957 if (max_cyc) 958 *max_cyc = max_cycles; 959 960 /* Return 50% of the actual maximum, so we can detect bad values */ 961 max_nsecs >>= 1; 962 963 return max_nsecs; 964 } 965 966 /** 967 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles 968 * @cs: Pointer to clocksource to be updated 969 * 970 */ 971 static inline void clocksource_update_max_deferment(struct clocksource *cs) 972 { 973 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift, 974 cs->maxadj, cs->mask, 975 &cs->max_cycles); 976 } 977 978 static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur) 979 { 980 struct clocksource *cs; 981 982 if (!finished_booting || list_empty(&clocksource_list)) 983 return NULL; 984 985 /* 986 * We pick the clocksource with the highest rating. If oneshot 987 * mode is active, we pick the highres valid clocksource with 988 * the best rating. 989 */ 990 list_for_each_entry(cs, &clocksource_list, list) { 991 if (skipcur && cs == curr_clocksource) 992 continue; 993 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 994 continue; 995 return cs; 996 } 997 return NULL; 998 } 999 1000 static void __clocksource_select(bool skipcur) 1001 { 1002 bool oneshot = tick_oneshot_mode_active(); 1003 struct clocksource *best, *cs; 1004 1005 /* Find the best suitable clocksource */ 1006 best = clocksource_find_best(oneshot, skipcur); 1007 if (!best) 1008 return; 1009 1010 if (!strlen(override_name)) 1011 goto found; 1012 1013 /* Check for the override clocksource. */ 1014 list_for_each_entry(cs, &clocksource_list, list) { 1015 if (skipcur && cs == curr_clocksource) 1016 continue; 1017 if (strcmp(cs->name, override_name) != 0) 1018 continue; 1019 /* 1020 * Check to make sure we don't switch to a non-highres 1021 * capable clocksource if the tick code is in oneshot 1022 * mode (highres or nohz) 1023 */ 1024 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) { 1025 /* Override clocksource cannot be used. */ 1026 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 1027 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n", 1028 cs->name); 1029 override_name[0] = 0; 1030 } else { 1031 /* 1032 * The override cannot be currently verified. 1033 * Deferring to let the watchdog check. 1034 */ 1035 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n", 1036 cs->name); 1037 } 1038 } else 1039 /* Override clocksource can be used. */ 1040 best = cs; 1041 break; 1042 } 1043 1044 found: 1045 if (curr_clocksource != best && !timekeeping_notify(best)) { 1046 pr_info("Switched to clocksource %s\n", best->name); 1047 curr_clocksource = best; 1048 } 1049 } 1050 1051 /** 1052 * clocksource_select - Select the best clocksource available 1053 * 1054 * Private function. Must hold clocksource_mutex when called. 1055 * 1056 * Select the clocksource with the best rating, or the clocksource, 1057 * which is selected by userspace override. 1058 */ 1059 static void clocksource_select(void) 1060 { 1061 __clocksource_select(false); 1062 } 1063 1064 static void clocksource_select_fallback(void) 1065 { 1066 __clocksource_select(true); 1067 } 1068 1069 /* 1070 * clocksource_done_booting - Called near the end of core bootup 1071 * 1072 * Hack to avoid lots of clocksource churn at boot time. 1073 * We use fs_initcall because we want this to start before 1074 * device_initcall but after subsys_initcall. 1075 */ 1076 static int __init clocksource_done_booting(void) 1077 { 1078 mutex_lock(&clocksource_mutex); 1079 curr_clocksource = clocksource_default_clock(); 1080 finished_booting = 1; 1081 /* 1082 * Run the watchdog first to eliminate unstable clock sources 1083 */ 1084 __clocksource_watchdog_kthread(); 1085 clocksource_select(); 1086 mutex_unlock(&clocksource_mutex); 1087 return 0; 1088 } 1089 fs_initcall(clocksource_done_booting); 1090 1091 /* 1092 * Enqueue the clocksource sorted by rating 1093 */ 1094 static void clocksource_enqueue(struct clocksource *cs) 1095 { 1096 struct list_head *entry = &clocksource_list; 1097 struct clocksource *tmp; 1098 1099 list_for_each_entry(tmp, &clocksource_list, list) { 1100 /* Keep track of the place, where to insert */ 1101 if (tmp->rating < cs->rating) 1102 break; 1103 entry = &tmp->list; 1104 } 1105 list_add(&cs->list, entry); 1106 } 1107 1108 /** 1109 * __clocksource_update_freq_scale - Used update clocksource with new freq 1110 * @cs: clocksource to be registered 1111 * @scale: Scale factor multiplied against freq to get clocksource hz 1112 * @freq: clocksource frequency (cycles per second) divided by scale 1113 * 1114 * This should only be called from the clocksource->enable() method. 1115 * 1116 * This *SHOULD NOT* be called directly! Please use the 1117 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper 1118 * functions. 1119 */ 1120 void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq) 1121 { 1122 u64 sec; 1123 1124 /* 1125 * Default clocksources are *special* and self-define their mult/shift. 1126 * But, you're not special, so you should specify a freq value. 1127 */ 1128 if (freq) { 1129 /* 1130 * Calc the maximum number of seconds which we can run before 1131 * wrapping around. For clocksources which have a mask > 32-bit 1132 * we need to limit the max sleep time to have a good 1133 * conversion precision. 10 minutes is still a reasonable 1134 * amount. That results in a shift value of 24 for a 1135 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to 1136 * ~ 0.06ppm granularity for NTP. 1137 */ 1138 sec = cs->mask; 1139 do_div(sec, freq); 1140 do_div(sec, scale); 1141 if (!sec) 1142 sec = 1; 1143 else if (sec > 600 && cs->mask > UINT_MAX) 1144 sec = 600; 1145 1146 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq, 1147 NSEC_PER_SEC / scale, sec * scale); 1148 } 1149 1150 /* 1151 * If the uncertainty margin is not specified, calculate it. 1152 * If both scale and freq are non-zero, calculate the clock 1153 * period, but bound below at 2*WATCHDOG_MAX_SKEW. However, 1154 * if either of scale or freq is zero, be very conservative and 1155 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the 1156 * uncertainty margin. Allow stupidly small uncertainty margins 1157 * to be specified by the caller for testing purposes, but warn 1158 * to discourage production use of this capability. 1159 */ 1160 if (scale && freq && !cs->uncertainty_margin) { 1161 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq); 1162 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW) 1163 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW; 1164 } else if (!cs->uncertainty_margin) { 1165 cs->uncertainty_margin = WATCHDOG_THRESHOLD; 1166 } 1167 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW); 1168 1169 /* 1170 * Ensure clocksources that have large 'mult' values don't overflow 1171 * when adjusted. 1172 */ 1173 cs->maxadj = clocksource_max_adjustment(cs); 1174 while (freq && ((cs->mult + cs->maxadj < cs->mult) 1175 || (cs->mult - cs->maxadj > cs->mult))) { 1176 cs->mult >>= 1; 1177 cs->shift--; 1178 cs->maxadj = clocksource_max_adjustment(cs); 1179 } 1180 1181 /* 1182 * Only warn for *special* clocksources that self-define 1183 * their mult/shift values and don't specify a freq. 1184 */ 1185 WARN_ONCE(cs->mult + cs->maxadj < cs->mult, 1186 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n", 1187 cs->name); 1188 1189 clocksource_update_max_deferment(cs); 1190 1191 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n", 1192 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns); 1193 } 1194 EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale); 1195 1196 /** 1197 * __clocksource_register_scale - Used to install new clocksources 1198 * @cs: clocksource to be registered 1199 * @scale: Scale factor multiplied against freq to get clocksource hz 1200 * @freq: clocksource frequency (cycles per second) divided by scale 1201 * 1202 * Returns -EBUSY if registration fails, zero otherwise. 1203 * 1204 * This *SHOULD NOT* be called directly! Please use the 1205 * clocksource_register_hz() or clocksource_register_khz helper functions. 1206 */ 1207 int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq) 1208 { 1209 unsigned long flags; 1210 1211 clocksource_arch_init(cs); 1212 1213 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX)) 1214 cs->id = CSID_GENERIC; 1215 if (cs->vdso_clock_mode < 0 || 1216 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) { 1217 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n", 1218 cs->name, cs->vdso_clock_mode); 1219 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE; 1220 } 1221 1222 /* Initialize mult/shift and max_idle_ns */ 1223 __clocksource_update_freq_scale(cs, scale, freq); 1224 1225 /* Add clocksource to the clocksource list */ 1226 mutex_lock(&clocksource_mutex); 1227 1228 clocksource_watchdog_lock(&flags); 1229 clocksource_enqueue(cs); 1230 clocksource_enqueue_watchdog(cs); 1231 clocksource_watchdog_unlock(&flags); 1232 1233 clocksource_select(); 1234 clocksource_select_watchdog(false); 1235 __clocksource_suspend_select(cs); 1236 mutex_unlock(&clocksource_mutex); 1237 return 0; 1238 } 1239 EXPORT_SYMBOL_GPL(__clocksource_register_scale); 1240 1241 static void __clocksource_change_rating(struct clocksource *cs, int rating) 1242 { 1243 list_del(&cs->list); 1244 cs->rating = rating; 1245 clocksource_enqueue(cs); 1246 } 1247 1248 /** 1249 * clocksource_change_rating - Change the rating of a registered clocksource 1250 * @cs: clocksource to be changed 1251 * @rating: new rating 1252 */ 1253 void clocksource_change_rating(struct clocksource *cs, int rating) 1254 { 1255 unsigned long flags; 1256 1257 mutex_lock(&clocksource_mutex); 1258 clocksource_watchdog_lock(&flags); 1259 __clocksource_change_rating(cs, rating); 1260 clocksource_watchdog_unlock(&flags); 1261 1262 clocksource_select(); 1263 clocksource_select_watchdog(false); 1264 clocksource_suspend_select(false); 1265 mutex_unlock(&clocksource_mutex); 1266 } 1267 EXPORT_SYMBOL(clocksource_change_rating); 1268 1269 /* 1270 * Unbind clocksource @cs. Called with clocksource_mutex held 1271 */ 1272 static int clocksource_unbind(struct clocksource *cs) 1273 { 1274 unsigned long flags; 1275 1276 if (clocksource_is_watchdog(cs)) { 1277 /* Select and try to install a replacement watchdog. */ 1278 clocksource_select_watchdog(true); 1279 if (clocksource_is_watchdog(cs)) 1280 return -EBUSY; 1281 } 1282 1283 if (cs == curr_clocksource) { 1284 /* Select and try to install a replacement clock source */ 1285 clocksource_select_fallback(); 1286 if (curr_clocksource == cs) 1287 return -EBUSY; 1288 } 1289 1290 if (clocksource_is_suspend(cs)) { 1291 /* 1292 * Select and try to install a replacement suspend clocksource. 1293 * If no replacement suspend clocksource, we will just let the 1294 * clocksource go and have no suspend clocksource. 1295 */ 1296 clocksource_suspend_select(true); 1297 } 1298 1299 clocksource_watchdog_lock(&flags); 1300 clocksource_dequeue_watchdog(cs); 1301 list_del_init(&cs->list); 1302 clocksource_watchdog_unlock(&flags); 1303 1304 return 0; 1305 } 1306 1307 /** 1308 * clocksource_unregister - remove a registered clocksource 1309 * @cs: clocksource to be unregistered 1310 */ 1311 int clocksource_unregister(struct clocksource *cs) 1312 { 1313 int ret = 0; 1314 1315 mutex_lock(&clocksource_mutex); 1316 if (!list_empty(&cs->list)) 1317 ret = clocksource_unbind(cs); 1318 mutex_unlock(&clocksource_mutex); 1319 return ret; 1320 } 1321 EXPORT_SYMBOL(clocksource_unregister); 1322 1323 #ifdef CONFIG_SYSFS 1324 /** 1325 * current_clocksource_show - sysfs interface for current clocksource 1326 * @dev: unused 1327 * @attr: unused 1328 * @buf: char buffer to be filled with clocksource list 1329 * 1330 * Provides sysfs interface for listing current clocksource. 1331 */ 1332 static ssize_t current_clocksource_show(struct device *dev, 1333 struct device_attribute *attr, 1334 char *buf) 1335 { 1336 ssize_t count = 0; 1337 1338 mutex_lock(&clocksource_mutex); 1339 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name); 1340 mutex_unlock(&clocksource_mutex); 1341 1342 return count; 1343 } 1344 1345 ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt) 1346 { 1347 size_t ret = cnt; 1348 1349 /* strings from sysfs write are not 0 terminated! */ 1350 if (!cnt || cnt >= CS_NAME_LEN) 1351 return -EINVAL; 1352 1353 /* strip of \n: */ 1354 if (buf[cnt-1] == '\n') 1355 cnt--; 1356 if (cnt > 0) 1357 memcpy(dst, buf, cnt); 1358 dst[cnt] = 0; 1359 return ret; 1360 } 1361 1362 /** 1363 * current_clocksource_store - interface for manually overriding clocksource 1364 * @dev: unused 1365 * @attr: unused 1366 * @buf: name of override clocksource 1367 * @count: length of buffer 1368 * 1369 * Takes input from sysfs interface for manually overriding the default 1370 * clocksource selection. 1371 */ 1372 static ssize_t current_clocksource_store(struct device *dev, 1373 struct device_attribute *attr, 1374 const char *buf, size_t count) 1375 { 1376 ssize_t ret; 1377 1378 mutex_lock(&clocksource_mutex); 1379 1380 ret = sysfs_get_uname(buf, override_name, count); 1381 if (ret >= 0) 1382 clocksource_select(); 1383 1384 mutex_unlock(&clocksource_mutex); 1385 1386 return ret; 1387 } 1388 static DEVICE_ATTR_RW(current_clocksource); 1389 1390 /** 1391 * unbind_clocksource_store - interface for manually unbinding clocksource 1392 * @dev: unused 1393 * @attr: unused 1394 * @buf: unused 1395 * @count: length of buffer 1396 * 1397 * Takes input from sysfs interface for manually unbinding a clocksource. 1398 */ 1399 static ssize_t unbind_clocksource_store(struct device *dev, 1400 struct device_attribute *attr, 1401 const char *buf, size_t count) 1402 { 1403 struct clocksource *cs; 1404 char name[CS_NAME_LEN]; 1405 ssize_t ret; 1406 1407 ret = sysfs_get_uname(buf, name, count); 1408 if (ret < 0) 1409 return ret; 1410 1411 ret = -ENODEV; 1412 mutex_lock(&clocksource_mutex); 1413 list_for_each_entry(cs, &clocksource_list, list) { 1414 if (strcmp(cs->name, name)) 1415 continue; 1416 ret = clocksource_unbind(cs); 1417 break; 1418 } 1419 mutex_unlock(&clocksource_mutex); 1420 1421 return ret ? ret : count; 1422 } 1423 static DEVICE_ATTR_WO(unbind_clocksource); 1424 1425 /** 1426 * available_clocksource_show - sysfs interface for listing clocksource 1427 * @dev: unused 1428 * @attr: unused 1429 * @buf: char buffer to be filled with clocksource list 1430 * 1431 * Provides sysfs interface for listing registered clocksources 1432 */ 1433 static ssize_t available_clocksource_show(struct device *dev, 1434 struct device_attribute *attr, 1435 char *buf) 1436 { 1437 struct clocksource *src; 1438 ssize_t count = 0; 1439 1440 mutex_lock(&clocksource_mutex); 1441 list_for_each_entry(src, &clocksource_list, list) { 1442 /* 1443 * Don't show non-HRES clocksource if the tick code is 1444 * in one shot mode (highres=on or nohz=on) 1445 */ 1446 if (!tick_oneshot_mode_active() || 1447 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 1448 count += snprintf(buf + count, 1449 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), 1450 "%s ", src->name); 1451 } 1452 mutex_unlock(&clocksource_mutex); 1453 1454 count += snprintf(buf + count, 1455 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n"); 1456 1457 return count; 1458 } 1459 static DEVICE_ATTR_RO(available_clocksource); 1460 1461 static struct attribute *clocksource_attrs[] = { 1462 &dev_attr_current_clocksource.attr, 1463 &dev_attr_unbind_clocksource.attr, 1464 &dev_attr_available_clocksource.attr, 1465 NULL 1466 }; 1467 ATTRIBUTE_GROUPS(clocksource); 1468 1469 static struct bus_type clocksource_subsys = { 1470 .name = "clocksource", 1471 .dev_name = "clocksource", 1472 }; 1473 1474 static struct device device_clocksource = { 1475 .id = 0, 1476 .bus = &clocksource_subsys, 1477 .groups = clocksource_groups, 1478 }; 1479 1480 static int __init init_clocksource_sysfs(void) 1481 { 1482 int error = subsys_system_register(&clocksource_subsys, NULL); 1483 1484 if (!error) 1485 error = device_register(&device_clocksource); 1486 1487 return error; 1488 } 1489 1490 device_initcall(init_clocksource_sysfs); 1491 #endif /* CONFIG_SYSFS */ 1492 1493 /** 1494 * boot_override_clocksource - boot clock override 1495 * @str: override name 1496 * 1497 * Takes a clocksource= boot argument and uses it 1498 * as the clocksource override name. 1499 */ 1500 static int __init boot_override_clocksource(char* str) 1501 { 1502 mutex_lock(&clocksource_mutex); 1503 if (str) 1504 strscpy(override_name, str, sizeof(override_name)); 1505 mutex_unlock(&clocksource_mutex); 1506 return 1; 1507 } 1508 1509 __setup("clocksource=", boot_override_clocksource); 1510 1511 /** 1512 * boot_override_clock - Compatibility layer for deprecated boot option 1513 * @str: override name 1514 * 1515 * DEPRECATED! Takes a clock= boot argument and uses it 1516 * as the clocksource override name 1517 */ 1518 static int __init boot_override_clock(char* str) 1519 { 1520 if (!strcmp(str, "pmtmr")) { 1521 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n"); 1522 return boot_override_clocksource("acpi_pm"); 1523 } 1524 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n"); 1525 return boot_override_clocksource(str); 1526 } 1527 1528 __setup("clock=", boot_override_clock); 1529