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 ulong max_cswd_read_retries = 2; 214 module_param(max_cswd_read_retries, ulong, 0644); 215 EXPORT_SYMBOL_GPL(max_cswd_read_retries); 216 static int verify_n_cpus = 8; 217 module_param(verify_n_cpus, int, 0644); 218 219 enum wd_read_status { 220 WD_READ_SUCCESS, 221 WD_READ_UNSTABLE, 222 WD_READ_SKIP 223 }; 224 225 static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow) 226 { 227 unsigned int nretries; 228 u64 wd_end, wd_end2, wd_delta; 229 int64_t wd_delay, wd_seq_delay; 230 231 for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) { 232 local_irq_disable(); 233 *wdnow = watchdog->read(watchdog); 234 *csnow = cs->read(cs); 235 wd_end = watchdog->read(watchdog); 236 wd_end2 = watchdog->read(watchdog); 237 local_irq_enable(); 238 239 wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask); 240 wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, 241 watchdog->shift); 242 if (wd_delay <= WATCHDOG_MAX_SKEW) { 243 if (nretries > 1 || nretries >= max_cswd_read_retries) { 244 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n", 245 smp_processor_id(), watchdog->name, nretries); 246 } 247 return WD_READ_SUCCESS; 248 } 249 250 /* 251 * Now compute delay in consecutive watchdog read to see if 252 * there is too much external interferences that cause 253 * significant delay in reading both clocksource and watchdog. 254 * 255 * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2, 256 * report system busy, reinit the watchdog and skip the current 257 * watchdog test. 258 */ 259 wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask); 260 wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift); 261 if (wd_seq_delay > WATCHDOG_MAX_SKEW/2) 262 goto skip_test; 263 } 264 265 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", 266 smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name); 267 return WD_READ_UNSTABLE; 268 269 skip_test: 270 pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n", 271 smp_processor_id(), watchdog->name, wd_seq_delay); 272 pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n", 273 cs->name, wd_delay); 274 return WD_READ_SKIP; 275 } 276 277 static u64 csnow_mid; 278 static cpumask_t cpus_ahead; 279 static cpumask_t cpus_behind; 280 static cpumask_t cpus_chosen; 281 282 static void clocksource_verify_choose_cpus(void) 283 { 284 int cpu, i, n = verify_n_cpus; 285 286 if (n < 0) { 287 /* Check all of the CPUs. */ 288 cpumask_copy(&cpus_chosen, cpu_online_mask); 289 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); 290 return; 291 } 292 293 /* If no checking desired, or no other CPU to check, leave. */ 294 cpumask_clear(&cpus_chosen); 295 if (n == 0 || num_online_cpus() <= 1) 296 return; 297 298 /* Make sure to select at least one CPU other than the current CPU. */ 299 cpu = cpumask_first(cpu_online_mask); 300 if (cpu == smp_processor_id()) 301 cpu = cpumask_next(cpu, cpu_online_mask); 302 if (WARN_ON_ONCE(cpu >= nr_cpu_ids)) 303 return; 304 cpumask_set_cpu(cpu, &cpus_chosen); 305 306 /* Force a sane value for the boot parameter. */ 307 if (n > nr_cpu_ids) 308 n = nr_cpu_ids; 309 310 /* 311 * Randomly select the specified number of CPUs. If the same 312 * CPU is selected multiple times, that CPU is checked only once, 313 * and no replacement CPU is selected. This gracefully handles 314 * situations where verify_n_cpus is greater than the number of 315 * CPUs that are currently online. 316 */ 317 for (i = 1; i < n; i++) { 318 cpu = get_random_u32_below(nr_cpu_ids); 319 cpu = cpumask_next(cpu - 1, cpu_online_mask); 320 if (cpu >= nr_cpu_ids) 321 cpu = cpumask_first(cpu_online_mask); 322 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids)) 323 cpumask_set_cpu(cpu, &cpus_chosen); 324 } 325 326 /* Don't verify ourselves. */ 327 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); 328 } 329 330 static void clocksource_verify_one_cpu(void *csin) 331 { 332 struct clocksource *cs = (struct clocksource *)csin; 333 334 csnow_mid = cs->read(cs); 335 } 336 337 void clocksource_verify_percpu(struct clocksource *cs) 338 { 339 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX; 340 u64 csnow_begin, csnow_end; 341 int cpu, testcpu; 342 s64 delta; 343 344 if (verify_n_cpus == 0) 345 return; 346 cpumask_clear(&cpus_ahead); 347 cpumask_clear(&cpus_behind); 348 cpus_read_lock(); 349 preempt_disable(); 350 clocksource_verify_choose_cpus(); 351 if (cpumask_empty(&cpus_chosen)) { 352 preempt_enable(); 353 cpus_read_unlock(); 354 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name); 355 return; 356 } 357 testcpu = smp_processor_id(); 358 pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen)); 359 for_each_cpu(cpu, &cpus_chosen) { 360 if (cpu == testcpu) 361 continue; 362 csnow_begin = cs->read(cs); 363 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1); 364 csnow_end = cs->read(cs); 365 delta = (s64)((csnow_mid - csnow_begin) & cs->mask); 366 if (delta < 0) 367 cpumask_set_cpu(cpu, &cpus_behind); 368 delta = (csnow_end - csnow_mid) & cs->mask; 369 if (delta < 0) 370 cpumask_set_cpu(cpu, &cpus_ahead); 371 delta = clocksource_delta(csnow_end, csnow_begin, cs->mask); 372 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift); 373 if (cs_nsec > cs_nsec_max) 374 cs_nsec_max = cs_nsec; 375 if (cs_nsec < cs_nsec_min) 376 cs_nsec_min = cs_nsec; 377 } 378 preempt_enable(); 379 cpus_read_unlock(); 380 if (!cpumask_empty(&cpus_ahead)) 381 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n", 382 cpumask_pr_args(&cpus_ahead), testcpu, cs->name); 383 if (!cpumask_empty(&cpus_behind)) 384 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n", 385 cpumask_pr_args(&cpus_behind), testcpu, cs->name); 386 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind)) 387 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n", 388 testcpu, cs_nsec_min, cs_nsec_max, cs->name); 389 } 390 EXPORT_SYMBOL_GPL(clocksource_verify_percpu); 391 392 static inline void clocksource_reset_watchdog(void) 393 { 394 struct clocksource *cs; 395 396 list_for_each_entry(cs, &watchdog_list, wd_list) 397 cs->flags &= ~CLOCK_SOURCE_WATCHDOG; 398 } 399 400 401 static void clocksource_watchdog(struct timer_list *unused) 402 { 403 u64 csnow, wdnow, cslast, wdlast, delta; 404 int64_t wd_nsec, cs_nsec, interval; 405 int next_cpu, reset_pending; 406 struct clocksource *cs; 407 enum wd_read_status read_ret; 408 unsigned long extra_wait = 0; 409 u32 md; 410 411 spin_lock(&watchdog_lock); 412 if (!watchdog_running) 413 goto out; 414 415 reset_pending = atomic_read(&watchdog_reset_pending); 416 417 list_for_each_entry(cs, &watchdog_list, wd_list) { 418 419 /* Clocksource already marked unstable? */ 420 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 421 if (finished_booting) 422 schedule_work(&watchdog_work); 423 continue; 424 } 425 426 read_ret = cs_watchdog_read(cs, &csnow, &wdnow); 427 428 if (read_ret == WD_READ_UNSTABLE) { 429 /* Clock readout unreliable, so give it up. */ 430 __clocksource_unstable(cs); 431 continue; 432 } 433 434 /* 435 * When WD_READ_SKIP is returned, it means the system is likely 436 * under very heavy load, where the latency of reading 437 * watchdog/clocksource is very big, and affect the accuracy of 438 * watchdog check. So give system some space and suspend the 439 * watchdog check for 5 minutes. 440 */ 441 if (read_ret == WD_READ_SKIP) { 442 /* 443 * As the watchdog timer will be suspended, and 444 * cs->last could keep unchanged for 5 minutes, reset 445 * the counters. 446 */ 447 clocksource_reset_watchdog(); 448 extra_wait = HZ * 300; 449 break; 450 } 451 452 /* Clocksource initialized ? */ 453 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) || 454 atomic_read(&watchdog_reset_pending)) { 455 cs->flags |= CLOCK_SOURCE_WATCHDOG; 456 cs->wd_last = wdnow; 457 cs->cs_last = csnow; 458 continue; 459 } 460 461 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask); 462 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult, 463 watchdog->shift); 464 465 delta = clocksource_delta(csnow, cs->cs_last, cs->mask); 466 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift); 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, delta, 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 delta = clocksource_delta(now, suspend_start, 854 suspend_clocksource->mask); 855 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult, 856 suspend_clocksource->shift); 857 } 858 859 /* 860 * Disable the suspend timer to save power if current clocksource is 861 * not the suspend timer. 862 */ 863 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable) 864 suspend_clocksource->disable(suspend_clocksource); 865 866 return nsec; 867 } 868 869 /** 870 * clocksource_suspend - suspend the clocksource(s) 871 */ 872 void clocksource_suspend(void) 873 { 874 struct clocksource *cs; 875 876 list_for_each_entry_reverse(cs, &clocksource_list, list) 877 if (cs->suspend) 878 cs->suspend(cs); 879 } 880 881 /** 882 * clocksource_resume - resume the clocksource(s) 883 */ 884 void clocksource_resume(void) 885 { 886 struct clocksource *cs; 887 888 list_for_each_entry(cs, &clocksource_list, list) 889 if (cs->resume) 890 cs->resume(cs); 891 892 clocksource_resume_watchdog(); 893 } 894 895 /** 896 * clocksource_touch_watchdog - Update watchdog 897 * 898 * Update the watchdog after exception contexts such as kgdb so as not 899 * to incorrectly trip the watchdog. This might fail when the kernel 900 * was stopped in code which holds watchdog_lock. 901 */ 902 void clocksource_touch_watchdog(void) 903 { 904 clocksource_resume_watchdog(); 905 } 906 907 /** 908 * clocksource_max_adjustment- Returns max adjustment amount 909 * @cs: Pointer to clocksource 910 * 911 */ 912 static u32 clocksource_max_adjustment(struct clocksource *cs) 913 { 914 u64 ret; 915 /* 916 * We won't try to correct for more than 11% adjustments (110,000 ppm), 917 */ 918 ret = (u64)cs->mult * 11; 919 do_div(ret,100); 920 return (u32)ret; 921 } 922 923 /** 924 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted 925 * @mult: cycle to nanosecond multiplier 926 * @shift: cycle to nanosecond divisor (power of two) 927 * @maxadj: maximum adjustment value to mult (~11%) 928 * @mask: bitmask for two's complement subtraction of non 64 bit counters 929 * @max_cyc: maximum cycle value before potential overflow (does not include 930 * any safety margin) 931 * 932 * NOTE: This function includes a safety margin of 50%, in other words, we 933 * return half the number of nanoseconds the hardware counter can technically 934 * cover. This is done so that we can potentially detect problems caused by 935 * delayed timers or bad hardware, which might result in time intervals that 936 * are larger than what the math used can handle without overflows. 937 */ 938 u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc) 939 { 940 u64 max_nsecs, max_cycles; 941 942 /* 943 * Calculate the maximum number of cycles that we can pass to the 944 * cyc2ns() function without overflowing a 64-bit result. 945 */ 946 max_cycles = ULLONG_MAX; 947 do_div(max_cycles, mult+maxadj); 948 949 /* 950 * The actual maximum number of cycles we can defer the clocksource is 951 * determined by the minimum of max_cycles and mask. 952 * Note: Here we subtract the maxadj to make sure we don't sleep for 953 * too long if there's a large negative adjustment. 954 */ 955 max_cycles = min(max_cycles, mask); 956 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift); 957 958 /* return the max_cycles value as well if requested */ 959 if (max_cyc) 960 *max_cyc = max_cycles; 961 962 /* Return 50% of the actual maximum, so we can detect bad values */ 963 max_nsecs >>= 1; 964 965 return max_nsecs; 966 } 967 968 /** 969 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles 970 * @cs: Pointer to clocksource to be updated 971 * 972 */ 973 static inline void clocksource_update_max_deferment(struct clocksource *cs) 974 { 975 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift, 976 cs->maxadj, cs->mask, 977 &cs->max_cycles); 978 } 979 980 static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur) 981 { 982 struct clocksource *cs; 983 984 if (!finished_booting || list_empty(&clocksource_list)) 985 return NULL; 986 987 /* 988 * We pick the clocksource with the highest rating. If oneshot 989 * mode is active, we pick the highres valid clocksource with 990 * the best rating. 991 */ 992 list_for_each_entry(cs, &clocksource_list, list) { 993 if (skipcur && cs == curr_clocksource) 994 continue; 995 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 996 continue; 997 return cs; 998 } 999 return NULL; 1000 } 1001 1002 static void __clocksource_select(bool skipcur) 1003 { 1004 bool oneshot = tick_oneshot_mode_active(); 1005 struct clocksource *best, *cs; 1006 1007 /* Find the best suitable clocksource */ 1008 best = clocksource_find_best(oneshot, skipcur); 1009 if (!best) 1010 return; 1011 1012 if (!strlen(override_name)) 1013 goto found; 1014 1015 /* Check for the override clocksource. */ 1016 list_for_each_entry(cs, &clocksource_list, list) { 1017 if (skipcur && cs == curr_clocksource) 1018 continue; 1019 if (strcmp(cs->name, override_name) != 0) 1020 continue; 1021 /* 1022 * Check to make sure we don't switch to a non-highres 1023 * capable clocksource if the tick code is in oneshot 1024 * mode (highres or nohz) 1025 */ 1026 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) { 1027 /* Override clocksource cannot be used. */ 1028 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 1029 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n", 1030 cs->name); 1031 override_name[0] = 0; 1032 } else { 1033 /* 1034 * The override cannot be currently verified. 1035 * Deferring to let the watchdog check. 1036 */ 1037 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n", 1038 cs->name); 1039 } 1040 } else 1041 /* Override clocksource can be used. */ 1042 best = cs; 1043 break; 1044 } 1045 1046 found: 1047 if (curr_clocksource != best && !timekeeping_notify(best)) { 1048 pr_info("Switched to clocksource %s\n", best->name); 1049 curr_clocksource = best; 1050 } 1051 } 1052 1053 /** 1054 * clocksource_select - Select the best clocksource available 1055 * 1056 * Private function. Must hold clocksource_mutex when called. 1057 * 1058 * Select the clocksource with the best rating, or the clocksource, 1059 * which is selected by userspace override. 1060 */ 1061 static void clocksource_select(void) 1062 { 1063 __clocksource_select(false); 1064 } 1065 1066 static void clocksource_select_fallback(void) 1067 { 1068 __clocksource_select(true); 1069 } 1070 1071 /* 1072 * clocksource_done_booting - Called near the end of core bootup 1073 * 1074 * Hack to avoid lots of clocksource churn at boot time. 1075 * We use fs_initcall because we want this to start before 1076 * device_initcall but after subsys_initcall. 1077 */ 1078 static int __init clocksource_done_booting(void) 1079 { 1080 mutex_lock(&clocksource_mutex); 1081 curr_clocksource = clocksource_default_clock(); 1082 finished_booting = 1; 1083 /* 1084 * Run the watchdog first to eliminate unstable clock sources 1085 */ 1086 __clocksource_watchdog_kthread(); 1087 clocksource_select(); 1088 mutex_unlock(&clocksource_mutex); 1089 return 0; 1090 } 1091 fs_initcall(clocksource_done_booting); 1092 1093 /* 1094 * Enqueue the clocksource sorted by rating 1095 */ 1096 static void clocksource_enqueue(struct clocksource *cs) 1097 { 1098 struct list_head *entry = &clocksource_list; 1099 struct clocksource *tmp; 1100 1101 list_for_each_entry(tmp, &clocksource_list, list) { 1102 /* Keep track of the place, where to insert */ 1103 if (tmp->rating < cs->rating) 1104 break; 1105 entry = &tmp->list; 1106 } 1107 list_add(&cs->list, entry); 1108 } 1109 1110 /** 1111 * __clocksource_update_freq_scale - Used update clocksource with new freq 1112 * @cs: clocksource to be registered 1113 * @scale: Scale factor multiplied against freq to get clocksource hz 1114 * @freq: clocksource frequency (cycles per second) divided by scale 1115 * 1116 * This should only be called from the clocksource->enable() method. 1117 * 1118 * This *SHOULD NOT* be called directly! Please use the 1119 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper 1120 * functions. 1121 */ 1122 void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq) 1123 { 1124 u64 sec; 1125 1126 /* 1127 * Default clocksources are *special* and self-define their mult/shift. 1128 * But, you're not special, so you should specify a freq value. 1129 */ 1130 if (freq) { 1131 /* 1132 * Calc the maximum number of seconds which we can run before 1133 * wrapping around. For clocksources which have a mask > 32-bit 1134 * we need to limit the max sleep time to have a good 1135 * conversion precision. 10 minutes is still a reasonable 1136 * amount. That results in a shift value of 24 for a 1137 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to 1138 * ~ 0.06ppm granularity for NTP. 1139 */ 1140 sec = cs->mask; 1141 do_div(sec, freq); 1142 do_div(sec, scale); 1143 if (!sec) 1144 sec = 1; 1145 else if (sec > 600 && cs->mask > UINT_MAX) 1146 sec = 600; 1147 1148 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq, 1149 NSEC_PER_SEC / scale, sec * scale); 1150 } 1151 1152 /* 1153 * If the uncertainty margin is not specified, calculate it. 1154 * If both scale and freq are non-zero, calculate the clock 1155 * period, but bound below at 2*WATCHDOG_MAX_SKEW. However, 1156 * if either of scale or freq is zero, be very conservative and 1157 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the 1158 * uncertainty margin. Allow stupidly small uncertainty margins 1159 * to be specified by the caller for testing purposes, but warn 1160 * to discourage production use of this capability. 1161 */ 1162 if (scale && freq && !cs->uncertainty_margin) { 1163 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq); 1164 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW) 1165 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW; 1166 } else if (!cs->uncertainty_margin) { 1167 cs->uncertainty_margin = WATCHDOG_THRESHOLD; 1168 } 1169 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW); 1170 1171 /* 1172 * Ensure clocksources that have large 'mult' values don't overflow 1173 * when adjusted. 1174 */ 1175 cs->maxadj = clocksource_max_adjustment(cs); 1176 while (freq && ((cs->mult + cs->maxadj < cs->mult) 1177 || (cs->mult - cs->maxadj > cs->mult))) { 1178 cs->mult >>= 1; 1179 cs->shift--; 1180 cs->maxadj = clocksource_max_adjustment(cs); 1181 } 1182 1183 /* 1184 * Only warn for *special* clocksources that self-define 1185 * their mult/shift values and don't specify a freq. 1186 */ 1187 WARN_ONCE(cs->mult + cs->maxadj < cs->mult, 1188 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n", 1189 cs->name); 1190 1191 clocksource_update_max_deferment(cs); 1192 1193 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n", 1194 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns); 1195 } 1196 EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale); 1197 1198 /** 1199 * __clocksource_register_scale - Used to install new clocksources 1200 * @cs: clocksource to be registered 1201 * @scale: Scale factor multiplied against freq to get clocksource hz 1202 * @freq: clocksource frequency (cycles per second) divided by scale 1203 * 1204 * Returns -EBUSY if registration fails, zero otherwise. 1205 * 1206 * This *SHOULD NOT* be called directly! Please use the 1207 * clocksource_register_hz() or clocksource_register_khz helper functions. 1208 */ 1209 int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq) 1210 { 1211 unsigned long flags; 1212 1213 clocksource_arch_init(cs); 1214 1215 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX)) 1216 cs->id = CSID_GENERIC; 1217 if (cs->vdso_clock_mode < 0 || 1218 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) { 1219 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n", 1220 cs->name, cs->vdso_clock_mode); 1221 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE; 1222 } 1223 1224 /* Initialize mult/shift and max_idle_ns */ 1225 __clocksource_update_freq_scale(cs, scale, freq); 1226 1227 /* Add clocksource to the clocksource list */ 1228 mutex_lock(&clocksource_mutex); 1229 1230 clocksource_watchdog_lock(&flags); 1231 clocksource_enqueue(cs); 1232 clocksource_enqueue_watchdog(cs); 1233 clocksource_watchdog_unlock(&flags); 1234 1235 clocksource_select(); 1236 clocksource_select_watchdog(false); 1237 __clocksource_suspend_select(cs); 1238 mutex_unlock(&clocksource_mutex); 1239 return 0; 1240 } 1241 EXPORT_SYMBOL_GPL(__clocksource_register_scale); 1242 1243 static void __clocksource_change_rating(struct clocksource *cs, int rating) 1244 { 1245 list_del(&cs->list); 1246 cs->rating = rating; 1247 clocksource_enqueue(cs); 1248 } 1249 1250 /** 1251 * clocksource_change_rating - Change the rating of a registered clocksource 1252 * @cs: clocksource to be changed 1253 * @rating: new rating 1254 */ 1255 void clocksource_change_rating(struct clocksource *cs, int rating) 1256 { 1257 unsigned long flags; 1258 1259 mutex_lock(&clocksource_mutex); 1260 clocksource_watchdog_lock(&flags); 1261 __clocksource_change_rating(cs, rating); 1262 clocksource_watchdog_unlock(&flags); 1263 1264 clocksource_select(); 1265 clocksource_select_watchdog(false); 1266 clocksource_suspend_select(false); 1267 mutex_unlock(&clocksource_mutex); 1268 } 1269 EXPORT_SYMBOL(clocksource_change_rating); 1270 1271 /* 1272 * Unbind clocksource @cs. Called with clocksource_mutex held 1273 */ 1274 static int clocksource_unbind(struct clocksource *cs) 1275 { 1276 unsigned long flags; 1277 1278 if (clocksource_is_watchdog(cs)) { 1279 /* Select and try to install a replacement watchdog. */ 1280 clocksource_select_watchdog(true); 1281 if (clocksource_is_watchdog(cs)) 1282 return -EBUSY; 1283 } 1284 1285 if (cs == curr_clocksource) { 1286 /* Select and try to install a replacement clock source */ 1287 clocksource_select_fallback(); 1288 if (curr_clocksource == cs) 1289 return -EBUSY; 1290 } 1291 1292 if (clocksource_is_suspend(cs)) { 1293 /* 1294 * Select and try to install a replacement suspend clocksource. 1295 * If no replacement suspend clocksource, we will just let the 1296 * clocksource go and have no suspend clocksource. 1297 */ 1298 clocksource_suspend_select(true); 1299 } 1300 1301 clocksource_watchdog_lock(&flags); 1302 clocksource_dequeue_watchdog(cs); 1303 list_del_init(&cs->list); 1304 clocksource_watchdog_unlock(&flags); 1305 1306 return 0; 1307 } 1308 1309 /** 1310 * clocksource_unregister - remove a registered clocksource 1311 * @cs: clocksource to be unregistered 1312 */ 1313 int clocksource_unregister(struct clocksource *cs) 1314 { 1315 int ret = 0; 1316 1317 mutex_lock(&clocksource_mutex); 1318 if (!list_empty(&cs->list)) 1319 ret = clocksource_unbind(cs); 1320 mutex_unlock(&clocksource_mutex); 1321 return ret; 1322 } 1323 EXPORT_SYMBOL(clocksource_unregister); 1324 1325 #ifdef CONFIG_SYSFS 1326 /** 1327 * current_clocksource_show - sysfs interface for current clocksource 1328 * @dev: unused 1329 * @attr: unused 1330 * @buf: char buffer to be filled with clocksource list 1331 * 1332 * Provides sysfs interface for listing current clocksource. 1333 */ 1334 static ssize_t current_clocksource_show(struct device *dev, 1335 struct device_attribute *attr, 1336 char *buf) 1337 { 1338 ssize_t count = 0; 1339 1340 mutex_lock(&clocksource_mutex); 1341 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name); 1342 mutex_unlock(&clocksource_mutex); 1343 1344 return count; 1345 } 1346 1347 ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt) 1348 { 1349 size_t ret = cnt; 1350 1351 /* strings from sysfs write are not 0 terminated! */ 1352 if (!cnt || cnt >= CS_NAME_LEN) 1353 return -EINVAL; 1354 1355 /* strip of \n: */ 1356 if (buf[cnt-1] == '\n') 1357 cnt--; 1358 if (cnt > 0) 1359 memcpy(dst, buf, cnt); 1360 dst[cnt] = 0; 1361 return ret; 1362 } 1363 1364 /** 1365 * current_clocksource_store - interface for manually overriding clocksource 1366 * @dev: unused 1367 * @attr: unused 1368 * @buf: name of override clocksource 1369 * @count: length of buffer 1370 * 1371 * Takes input from sysfs interface for manually overriding the default 1372 * clocksource selection. 1373 */ 1374 static ssize_t current_clocksource_store(struct device *dev, 1375 struct device_attribute *attr, 1376 const char *buf, size_t count) 1377 { 1378 ssize_t ret; 1379 1380 mutex_lock(&clocksource_mutex); 1381 1382 ret = sysfs_get_uname(buf, override_name, count); 1383 if (ret >= 0) 1384 clocksource_select(); 1385 1386 mutex_unlock(&clocksource_mutex); 1387 1388 return ret; 1389 } 1390 static DEVICE_ATTR_RW(current_clocksource); 1391 1392 /** 1393 * unbind_clocksource_store - interface for manually unbinding clocksource 1394 * @dev: unused 1395 * @attr: unused 1396 * @buf: unused 1397 * @count: length of buffer 1398 * 1399 * Takes input from sysfs interface for manually unbinding a clocksource. 1400 */ 1401 static ssize_t unbind_clocksource_store(struct device *dev, 1402 struct device_attribute *attr, 1403 const char *buf, size_t count) 1404 { 1405 struct clocksource *cs; 1406 char name[CS_NAME_LEN]; 1407 ssize_t ret; 1408 1409 ret = sysfs_get_uname(buf, name, count); 1410 if (ret < 0) 1411 return ret; 1412 1413 ret = -ENODEV; 1414 mutex_lock(&clocksource_mutex); 1415 list_for_each_entry(cs, &clocksource_list, list) { 1416 if (strcmp(cs->name, name)) 1417 continue; 1418 ret = clocksource_unbind(cs); 1419 break; 1420 } 1421 mutex_unlock(&clocksource_mutex); 1422 1423 return ret ? ret : count; 1424 } 1425 static DEVICE_ATTR_WO(unbind_clocksource); 1426 1427 /** 1428 * available_clocksource_show - sysfs interface for listing clocksource 1429 * @dev: unused 1430 * @attr: unused 1431 * @buf: char buffer to be filled with clocksource list 1432 * 1433 * Provides sysfs interface for listing registered clocksources 1434 */ 1435 static ssize_t available_clocksource_show(struct device *dev, 1436 struct device_attribute *attr, 1437 char *buf) 1438 { 1439 struct clocksource *src; 1440 ssize_t count = 0; 1441 1442 mutex_lock(&clocksource_mutex); 1443 list_for_each_entry(src, &clocksource_list, list) { 1444 /* 1445 * Don't show non-HRES clocksource if the tick code is 1446 * in one shot mode (highres=on or nohz=on) 1447 */ 1448 if (!tick_oneshot_mode_active() || 1449 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 1450 count += snprintf(buf + count, 1451 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), 1452 "%s ", src->name); 1453 } 1454 mutex_unlock(&clocksource_mutex); 1455 1456 count += snprintf(buf + count, 1457 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n"); 1458 1459 return count; 1460 } 1461 static DEVICE_ATTR_RO(available_clocksource); 1462 1463 static struct attribute *clocksource_attrs[] = { 1464 &dev_attr_current_clocksource.attr, 1465 &dev_attr_unbind_clocksource.attr, 1466 &dev_attr_available_clocksource.attr, 1467 NULL 1468 }; 1469 ATTRIBUTE_GROUPS(clocksource); 1470 1471 static struct bus_type clocksource_subsys = { 1472 .name = "clocksource", 1473 .dev_name = "clocksource", 1474 }; 1475 1476 static struct device device_clocksource = { 1477 .id = 0, 1478 .bus = &clocksource_subsys, 1479 .groups = clocksource_groups, 1480 }; 1481 1482 static int __init init_clocksource_sysfs(void) 1483 { 1484 int error = subsys_system_register(&clocksource_subsys, NULL); 1485 1486 if (!error) 1487 error = device_register(&device_clocksource); 1488 1489 return error; 1490 } 1491 1492 device_initcall(init_clocksource_sysfs); 1493 #endif /* CONFIG_SYSFS */ 1494 1495 /** 1496 * boot_override_clocksource - boot clock override 1497 * @str: override name 1498 * 1499 * Takes a clocksource= boot argument and uses it 1500 * as the clocksource override name. 1501 */ 1502 static int __init boot_override_clocksource(char* str) 1503 { 1504 mutex_lock(&clocksource_mutex); 1505 if (str) 1506 strscpy(override_name, str, sizeof(override_name)); 1507 mutex_unlock(&clocksource_mutex); 1508 return 1; 1509 } 1510 1511 __setup("clocksource=", boot_override_clocksource); 1512 1513 /** 1514 * boot_override_clock - Compatibility layer for deprecated boot option 1515 * @str: override name 1516 * 1517 * DEPRECATED! Takes a clock= boot argument and uses it 1518 * as the clocksource override name 1519 */ 1520 static int __init boot_override_clock(char* str) 1521 { 1522 if (!strcmp(str, "pmtmr")) { 1523 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n"); 1524 return boot_override_clocksource("acpi_pm"); 1525 } 1526 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n"); 1527 return boot_override_clocksource(str); 1528 } 1529 1530 __setup("clock=", boot_override_clock); 1531