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