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 void clocksource_enqueue(struct clocksource *cs); 24 25 static noinline u64 cycles_to_nsec_safe(struct clocksource *cs, u64 start, u64 end) 26 { 27 u64 delta = clocksource_delta(end, start, cs->mask, cs->max_raw_delta); 28 29 if (likely(delta < cs->max_cycles)) 30 return clocksource_cyc2ns(delta, cs->mult, cs->shift); 31 32 return mul_u64_u32_shr(delta, cs->mult, cs->shift); 33 } 34 35 /** 36 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks 37 * @mult: pointer to mult variable 38 * @shift: pointer to shift variable 39 * @from: frequency to convert from 40 * @to: frequency to convert to 41 * @maxsec: guaranteed runtime conversion range in seconds 42 * 43 * The function evaluates the shift/mult pair for the scaled math 44 * operations of clocksources and clockevents. 45 * 46 * @to and @from are frequency values in HZ. For clock sources @to is 47 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock 48 * event @to is the counter frequency and @from is NSEC_PER_SEC. 49 * 50 * The @maxsec conversion range argument controls the time frame in 51 * seconds which must be covered by the runtime conversion with the 52 * calculated mult and shift factors. This guarantees that no 64bit 53 * overflow happens when the input value of the conversion is 54 * multiplied with the calculated mult factor. Larger ranges may 55 * reduce the conversion accuracy by choosing smaller mult and shift 56 * factors. 57 */ 58 void 59 clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec) 60 { 61 u64 tmp; 62 u32 sft, sftacc= 32; 63 64 /* 65 * Calculate the shift factor which is limiting the conversion 66 * range: 67 */ 68 tmp = ((u64)maxsec * from) >> 32; 69 while (tmp) { 70 tmp >>=1; 71 sftacc--; 72 } 73 74 /* 75 * Find the conversion shift/mult pair which has the best 76 * accuracy and fits the maxsec conversion range: 77 */ 78 for (sft = 32; sft > 0; sft--) { 79 tmp = (u64) to << sft; 80 tmp += from / 2; 81 do_div(tmp, from); 82 if ((tmp >> sftacc) == 0) 83 break; 84 } 85 *mult = tmp; 86 *shift = sft; 87 } 88 EXPORT_SYMBOL_GPL(clocks_calc_mult_shift); 89 90 /*[Clocksource internal variables]--------- 91 * curr_clocksource: 92 * currently selected clocksource. 93 * suspend_clocksource: 94 * used to calculate the suspend time. 95 * clocksource_list: 96 * linked list with the registered clocksources 97 * clocksource_mutex: 98 * protects manipulations to curr_clocksource and the clocksource_list 99 * override_name: 100 * Name of the user-specified clocksource. 101 */ 102 static struct clocksource *curr_clocksource; 103 static struct clocksource *suspend_clocksource; 104 static LIST_HEAD(clocksource_list); 105 static DEFINE_MUTEX(clocksource_mutex); 106 static char override_name[CS_NAME_LEN]; 107 static int finished_booting; 108 static u64 suspend_start; 109 110 /* 111 * Interval: 0.5sec. 112 */ 113 #define WATCHDOG_INTERVAL (HZ >> 1) 114 #define WATCHDOG_INTERVAL_MAX_NS ((2 * WATCHDOG_INTERVAL) * (NSEC_PER_SEC / HZ)) 115 116 /* 117 * Threshold: 0.0312s, when doubled: 0.0625s. 118 */ 119 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5) 120 121 /* 122 * Maximum permissible delay between two readouts of the watchdog 123 * clocksource surrounding a read of the clocksource being validated. 124 * This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as 125 * a lower bound for cs->uncertainty_margin values when registering clocks. 126 * 127 * The default of 500 parts per million is based on NTP's limits. 128 * If a clocksource is good enough for NTP, it is good enough for us! 129 * 130 * In other words, by default, even if a clocksource is extremely 131 * precise (for example, with a sub-nanosecond period), the maximum 132 * permissible skew between the clocksource watchdog and the clocksource 133 * under test is not permitted to go below the 500ppm minimum defined 134 * by MAX_SKEW_USEC. This 500ppm minimum may be overridden using the 135 * CLOCKSOURCE_WATCHDOG_MAX_SKEW_US Kconfig option. 136 */ 137 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 138 #define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 139 #else 140 #define MAX_SKEW_USEC (125 * WATCHDOG_INTERVAL / HZ) 141 #endif 142 143 /* 144 * Default for maximum permissible skew when cs->uncertainty_margin is 145 * not specified, and the lower bound even when cs->uncertainty_margin 146 * is specified. This is also the default that is used when registering 147 * clocks with unspecified cs->uncertainty_margin, so this macro is used 148 * even in CONFIG_CLOCKSOURCE_WATCHDOG=n kernels. 149 */ 150 #define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC) 151 152 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG 153 static void clocksource_watchdog_work(struct work_struct *work); 154 static void clocksource_select(void); 155 156 static LIST_HEAD(watchdog_list); 157 static struct clocksource *watchdog; 158 static struct timer_list watchdog_timer; 159 static DECLARE_WORK(watchdog_work, clocksource_watchdog_work); 160 static DEFINE_SPINLOCK(watchdog_lock); 161 static int watchdog_running; 162 static atomic_t watchdog_reset_pending; 163 static int64_t watchdog_max_interval; 164 165 static inline void clocksource_watchdog_lock(unsigned long *flags) 166 { 167 spin_lock_irqsave(&watchdog_lock, *flags); 168 } 169 170 static inline void clocksource_watchdog_unlock(unsigned long *flags) 171 { 172 spin_unlock_irqrestore(&watchdog_lock, *flags); 173 } 174 175 static int clocksource_watchdog_kthread(void *data); 176 177 static void clocksource_watchdog_work(struct work_struct *work) 178 { 179 /* 180 * We cannot directly run clocksource_watchdog_kthread() here, because 181 * clocksource_select() calls timekeeping_notify() which uses 182 * stop_machine(). One cannot use stop_machine() from a workqueue() due 183 * lock inversions wrt CPU hotplug. 184 * 185 * Also, we only ever run this work once or twice during the lifetime 186 * of the kernel, so there is no point in creating a more permanent 187 * kthread for this. 188 * 189 * If kthread_run fails the next watchdog scan over the 190 * watchdog_list will find the unstable clock again. 191 */ 192 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog"); 193 } 194 195 static void clocksource_change_rating(struct clocksource *cs, int rating) 196 { 197 list_del(&cs->list); 198 cs->rating = rating; 199 clocksource_enqueue(cs); 200 } 201 202 static void __clocksource_unstable(struct clocksource *cs) 203 { 204 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG); 205 cs->flags |= CLOCK_SOURCE_UNSTABLE; 206 207 /* 208 * If the clocksource is registered clocksource_watchdog_kthread() will 209 * re-rate and re-select. 210 */ 211 if (list_empty(&cs->list)) { 212 cs->rating = 0; 213 return; 214 } 215 216 if (cs->mark_unstable) 217 cs->mark_unstable(cs); 218 219 /* kick clocksource_watchdog_kthread() */ 220 if (finished_booting) 221 schedule_work(&watchdog_work); 222 } 223 224 /** 225 * clocksource_mark_unstable - mark clocksource unstable via watchdog 226 * @cs: clocksource to be marked unstable 227 * 228 * This function is called by the x86 TSC code to mark clocksources as unstable; 229 * it defers demotion and re-selection to a kthread. 230 */ 231 void clocksource_mark_unstable(struct clocksource *cs) 232 { 233 unsigned long flags; 234 235 spin_lock_irqsave(&watchdog_lock, flags); 236 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) { 237 if (!list_empty(&cs->list) && list_empty(&cs->wd_list)) 238 list_add(&cs->wd_list, &watchdog_list); 239 __clocksource_unstable(cs); 240 } 241 spin_unlock_irqrestore(&watchdog_lock, flags); 242 } 243 244 static int verify_n_cpus = 8; 245 module_param(verify_n_cpus, int, 0644); 246 247 enum wd_read_status { 248 WD_READ_SUCCESS, 249 WD_READ_UNSTABLE, 250 WD_READ_SKIP 251 }; 252 253 static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow) 254 { 255 int64_t md = 2 * watchdog->uncertainty_margin; 256 unsigned int nretries, max_retries; 257 int64_t wd_delay, wd_seq_delay; 258 u64 wd_end, wd_end2; 259 260 max_retries = clocksource_get_max_watchdog_retry(); 261 for (nretries = 0; nretries <= max_retries; nretries++) { 262 local_irq_disable(); 263 *wdnow = watchdog->read(watchdog); 264 *csnow = cs->read(cs); 265 wd_end = watchdog->read(watchdog); 266 wd_end2 = watchdog->read(watchdog); 267 local_irq_enable(); 268 269 wd_delay = cycles_to_nsec_safe(watchdog, *wdnow, wd_end); 270 if (wd_delay <= md + cs->uncertainty_margin) { 271 if (nretries > 1 && nretries >= max_retries) { 272 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n", 273 smp_processor_id(), watchdog->name, nretries); 274 } 275 return WD_READ_SUCCESS; 276 } 277 278 /* 279 * Now compute delay in consecutive watchdog read to see if 280 * there is too much external interferences that cause 281 * significant delay in reading both clocksource and watchdog. 282 * 283 * If consecutive WD read-back delay > md, report 284 * system busy, reinit the watchdog and skip the current 285 * watchdog test. 286 */ 287 wd_seq_delay = cycles_to_nsec_safe(watchdog, wd_end, wd_end2); 288 if (wd_seq_delay > md) 289 goto skip_test; 290 } 291 292 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", 293 smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name); 294 return WD_READ_UNSTABLE; 295 296 skip_test: 297 pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n", 298 smp_processor_id(), watchdog->name, wd_seq_delay); 299 pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n", 300 cs->name, wd_delay); 301 return WD_READ_SKIP; 302 } 303 304 static u64 csnow_mid; 305 static cpumask_t cpus_ahead; 306 static cpumask_t cpus_behind; 307 static cpumask_t cpus_chosen; 308 309 static void clocksource_verify_choose_cpus(void) 310 { 311 int cpu, i, n = verify_n_cpus; 312 313 if (n < 0 || n >= num_online_cpus()) { 314 /* Check all of the CPUs. */ 315 cpumask_copy(&cpus_chosen, cpu_online_mask); 316 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); 317 return; 318 } 319 320 /* If no checking desired, or no other CPU to check, leave. */ 321 cpumask_clear(&cpus_chosen); 322 if (n == 0 || num_online_cpus() <= 1) 323 return; 324 325 /* Make sure to select at least one CPU other than the current CPU. */ 326 cpu = cpumask_any_but(cpu_online_mask, smp_processor_id()); 327 if (WARN_ON_ONCE(cpu >= nr_cpu_ids)) 328 return; 329 cpumask_set_cpu(cpu, &cpus_chosen); 330 331 /* Force a sane value for the boot parameter. */ 332 if (n > nr_cpu_ids) 333 n = nr_cpu_ids; 334 335 /* 336 * Randomly select the specified number of CPUs. If the same 337 * CPU is selected multiple times, that CPU is checked only once, 338 * and no replacement CPU is selected. This gracefully handles 339 * situations where verify_n_cpus is greater than the number of 340 * CPUs that are currently online. 341 */ 342 for (i = 1; i < n; i++) { 343 cpu = cpumask_random(cpu_online_mask); 344 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids)) 345 cpumask_set_cpu(cpu, &cpus_chosen); 346 } 347 348 /* Don't verify ourselves. */ 349 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); 350 } 351 352 static void clocksource_verify_one_cpu(void *csin) 353 { 354 struct clocksource *cs = (struct clocksource *)csin; 355 356 csnow_mid = cs->read(cs); 357 } 358 359 void clocksource_verify_percpu(struct clocksource *cs) 360 { 361 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX; 362 u64 csnow_begin, csnow_end; 363 int cpu, testcpu; 364 s64 delta; 365 366 if (verify_n_cpus == 0) 367 return; 368 cpumask_clear(&cpus_ahead); 369 cpumask_clear(&cpus_behind); 370 cpus_read_lock(); 371 migrate_disable(); 372 clocksource_verify_choose_cpus(); 373 if (cpumask_empty(&cpus_chosen)) { 374 migrate_enable(); 375 cpus_read_unlock(); 376 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name); 377 return; 378 } 379 testcpu = smp_processor_id(); 380 pr_info("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", 381 cs->name, testcpu, cpumask_pr_args(&cpus_chosen)); 382 preempt_disable(); 383 for_each_cpu(cpu, &cpus_chosen) { 384 if (cpu == testcpu) 385 continue; 386 csnow_begin = cs->read(cs); 387 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1); 388 csnow_end = cs->read(cs); 389 delta = (s64)((csnow_mid - csnow_begin) & cs->mask); 390 if (delta < 0) 391 cpumask_set_cpu(cpu, &cpus_behind); 392 delta = (csnow_end - csnow_mid) & cs->mask; 393 if (delta < 0) 394 cpumask_set_cpu(cpu, &cpus_ahead); 395 cs_nsec = cycles_to_nsec_safe(cs, csnow_begin, csnow_end); 396 if (cs_nsec > cs_nsec_max) 397 cs_nsec_max = cs_nsec; 398 if (cs_nsec < cs_nsec_min) 399 cs_nsec_min = cs_nsec; 400 } 401 preempt_enable(); 402 migrate_enable(); 403 cpus_read_unlock(); 404 if (!cpumask_empty(&cpus_ahead)) 405 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n", 406 cpumask_pr_args(&cpus_ahead), testcpu, cs->name); 407 if (!cpumask_empty(&cpus_behind)) 408 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n", 409 cpumask_pr_args(&cpus_behind), testcpu, cs->name); 410 pr_info(" CPU %d check durations %lldns - %lldns for clocksource %s.\n", 411 testcpu, cs_nsec_min, cs_nsec_max, cs->name); 412 } 413 EXPORT_SYMBOL_GPL(clocksource_verify_percpu); 414 415 static inline void clocksource_reset_watchdog(void) 416 { 417 struct clocksource *cs; 418 419 list_for_each_entry(cs, &watchdog_list, wd_list) 420 cs->flags &= ~CLOCK_SOURCE_WATCHDOG; 421 } 422 423 424 static void clocksource_watchdog(struct timer_list *unused) 425 { 426 int64_t wd_nsec, cs_nsec, interval; 427 u64 csnow, wdnow, cslast, wdlast; 428 int next_cpu, reset_pending; 429 struct clocksource *cs; 430 enum wd_read_status read_ret; 431 unsigned long extra_wait = 0; 432 u32 md; 433 434 spin_lock(&watchdog_lock); 435 if (!watchdog_running) 436 goto out; 437 438 reset_pending = atomic_read(&watchdog_reset_pending); 439 440 list_for_each_entry(cs, &watchdog_list, wd_list) { 441 442 /* Clocksource already marked unstable? */ 443 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 444 if (finished_booting) 445 schedule_work(&watchdog_work); 446 continue; 447 } 448 449 read_ret = cs_watchdog_read(cs, &csnow, &wdnow); 450 451 if (read_ret == WD_READ_UNSTABLE) { 452 /* Clock readout unreliable, so give it up. */ 453 __clocksource_unstable(cs); 454 continue; 455 } 456 457 /* 458 * When WD_READ_SKIP is returned, it means the system is likely 459 * under very heavy load, where the latency of reading 460 * watchdog/clocksource is very big, and affect the accuracy of 461 * watchdog check. So give system some space and suspend the 462 * watchdog check for 5 minutes. 463 */ 464 if (read_ret == WD_READ_SKIP) { 465 /* 466 * As the watchdog timer will be suspended, and 467 * cs->last could keep unchanged for 5 minutes, reset 468 * the counters. 469 */ 470 clocksource_reset_watchdog(); 471 extra_wait = HZ * 300; 472 break; 473 } 474 475 /* Clocksource initialized ? */ 476 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) || 477 atomic_read(&watchdog_reset_pending)) { 478 cs->flags |= CLOCK_SOURCE_WATCHDOG; 479 cs->wd_last = wdnow; 480 cs->cs_last = csnow; 481 continue; 482 } 483 484 wd_nsec = cycles_to_nsec_safe(watchdog, cs->wd_last, wdnow); 485 cs_nsec = cycles_to_nsec_safe(cs, cs->cs_last, csnow); 486 wdlast = cs->wd_last; /* save these in case we print them */ 487 cslast = cs->cs_last; 488 cs->cs_last = csnow; 489 cs->wd_last = wdnow; 490 491 if (atomic_read(&watchdog_reset_pending)) 492 continue; 493 494 /* 495 * The processing of timer softirqs can get delayed (usually 496 * on account of ksoftirqd not getting to run in a timely 497 * manner), which causes the watchdog interval to stretch. 498 * Skew detection may fail for longer watchdog intervals 499 * on account of fixed margins being used. 500 * Some clocksources, e.g. acpi_pm, cannot tolerate 501 * watchdog intervals longer than a few seconds. 502 */ 503 interval = max(cs_nsec, wd_nsec); 504 if (unlikely(interval > WATCHDOG_INTERVAL_MAX_NS)) { 505 if (system_state > SYSTEM_SCHEDULING && 506 interval > 2 * watchdog_max_interval) { 507 watchdog_max_interval = interval; 508 pr_warn("Long readout interval, skipping watchdog check: cs_nsec: %lld wd_nsec: %lld\n", 509 cs_nsec, wd_nsec); 510 } 511 watchdog_timer.expires = jiffies; 512 continue; 513 } 514 515 /* Check the deviation from the watchdog clocksource. */ 516 md = cs->uncertainty_margin + watchdog->uncertainty_margin; 517 if (abs(cs_nsec - wd_nsec) > md) { 518 s64 cs_wd_msec; 519 s64 wd_msec; 520 u32 wd_rem; 521 522 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n", 523 smp_processor_id(), cs->name); 524 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n", 525 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask); 526 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n", 527 cs->name, cs_nsec, csnow, cslast, cs->mask); 528 cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem); 529 wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem); 530 pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n", 531 cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec); 532 if (curr_clocksource == cs) 533 pr_warn(" '%s' is current clocksource.\n", cs->name); 534 else if (curr_clocksource) 535 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name); 536 else 537 pr_warn(" No current clocksource.\n"); 538 __clocksource_unstable(cs); 539 continue; 540 } 541 542 if (cs == curr_clocksource && cs->tick_stable) 543 cs->tick_stable(cs); 544 545 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && 546 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) && 547 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) { 548 /* Mark it valid for high-res. */ 549 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 550 551 /* 552 * clocksource_done_booting() will sort it if 553 * finished_booting is not set yet. 554 */ 555 if (!finished_booting) 556 continue; 557 558 /* 559 * If this is not the current clocksource let 560 * the watchdog thread reselect it. Due to the 561 * change to high res this clocksource might 562 * be preferred now. If it is the current 563 * clocksource let the tick code know about 564 * that change. 565 */ 566 if (cs != curr_clocksource) { 567 cs->flags |= CLOCK_SOURCE_RESELECT; 568 schedule_work(&watchdog_work); 569 } else { 570 tick_clock_notify(); 571 } 572 } 573 } 574 575 /* 576 * We only clear the watchdog_reset_pending, when we did a 577 * full cycle through all clocksources. 578 */ 579 if (reset_pending) 580 atomic_dec(&watchdog_reset_pending); 581 582 /* 583 * Cycle through CPUs to check if the CPUs stay synchronized 584 * to each other. 585 */ 586 next_cpu = cpumask_next_wrap(raw_smp_processor_id(), cpu_online_mask); 587 588 /* 589 * Arm timer if not already pending: could race with concurrent 590 * pair clocksource_stop_watchdog() clocksource_start_watchdog(). 591 */ 592 if (!timer_pending(&watchdog_timer)) { 593 watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait; 594 add_timer_on(&watchdog_timer, next_cpu); 595 } 596 out: 597 spin_unlock(&watchdog_lock); 598 } 599 600 static inline void clocksource_start_watchdog(void) 601 { 602 if (watchdog_running || !watchdog || list_empty(&watchdog_list)) 603 return; 604 timer_setup(&watchdog_timer, clocksource_watchdog, 0); 605 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL; 606 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask)); 607 watchdog_running = 1; 608 } 609 610 static inline void clocksource_stop_watchdog(void) 611 { 612 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list))) 613 return; 614 timer_delete(&watchdog_timer); 615 watchdog_running = 0; 616 } 617 618 static void clocksource_resume_watchdog(void) 619 { 620 atomic_inc(&watchdog_reset_pending); 621 } 622 623 static void clocksource_enqueue_watchdog(struct clocksource *cs) 624 { 625 INIT_LIST_HEAD(&cs->wd_list); 626 627 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { 628 /* cs is a clocksource to be watched. */ 629 list_add(&cs->wd_list, &watchdog_list); 630 cs->flags &= ~CLOCK_SOURCE_WATCHDOG; 631 } else { 632 /* cs is a watchdog. */ 633 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 634 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 635 } 636 } 637 638 static void clocksource_select_watchdog(bool fallback) 639 { 640 struct clocksource *cs, *old_wd; 641 unsigned long flags; 642 643 spin_lock_irqsave(&watchdog_lock, flags); 644 /* save current watchdog */ 645 old_wd = watchdog; 646 if (fallback) 647 watchdog = NULL; 648 649 list_for_each_entry(cs, &clocksource_list, list) { 650 /* cs is a clocksource to be watched. */ 651 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) 652 continue; 653 654 /* Skip current if we were requested for a fallback. */ 655 if (fallback && cs == old_wd) 656 continue; 657 658 /* Pick the best watchdog. */ 659 if (!watchdog || cs->rating > watchdog->rating) 660 watchdog = cs; 661 } 662 /* If we failed to find a fallback restore the old one. */ 663 if (!watchdog) 664 watchdog = old_wd; 665 666 /* If we changed the watchdog we need to reset cycles. */ 667 if (watchdog != old_wd) 668 clocksource_reset_watchdog(); 669 670 /* Check if the watchdog timer needs to be started. */ 671 clocksource_start_watchdog(); 672 spin_unlock_irqrestore(&watchdog_lock, flags); 673 } 674 675 static void clocksource_dequeue_watchdog(struct clocksource *cs) 676 { 677 if (cs != watchdog) { 678 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { 679 /* cs is a watched clocksource. */ 680 list_del_init(&cs->wd_list); 681 /* Check if the watchdog timer needs to be stopped. */ 682 clocksource_stop_watchdog(); 683 } 684 } 685 } 686 687 static int __clocksource_watchdog_kthread(void) 688 { 689 struct clocksource *cs, *tmp; 690 unsigned long flags; 691 int select = 0; 692 693 /* Do any required per-CPU skew verification. */ 694 if (curr_clocksource && 695 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE && 696 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU) 697 clocksource_verify_percpu(curr_clocksource); 698 699 spin_lock_irqsave(&watchdog_lock, flags); 700 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) { 701 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 702 list_del_init(&cs->wd_list); 703 clocksource_change_rating(cs, 0); 704 select = 1; 705 } 706 if (cs->flags & CLOCK_SOURCE_RESELECT) { 707 cs->flags &= ~CLOCK_SOURCE_RESELECT; 708 select = 1; 709 } 710 } 711 /* Check if the watchdog timer needs to be stopped. */ 712 clocksource_stop_watchdog(); 713 spin_unlock_irqrestore(&watchdog_lock, flags); 714 715 return select; 716 } 717 718 static int clocksource_watchdog_kthread(void *data) 719 { 720 mutex_lock(&clocksource_mutex); 721 if (__clocksource_watchdog_kthread()) 722 clocksource_select(); 723 mutex_unlock(&clocksource_mutex); 724 return 0; 725 } 726 727 static bool clocksource_is_watchdog(struct clocksource *cs) 728 { 729 return cs == watchdog; 730 } 731 732 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */ 733 734 static void clocksource_enqueue_watchdog(struct clocksource *cs) 735 { 736 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 737 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 738 } 739 740 static void clocksource_select_watchdog(bool fallback) { } 741 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { } 742 static inline void clocksource_resume_watchdog(void) { } 743 static inline int __clocksource_watchdog_kthread(void) { return 0; } 744 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; } 745 void clocksource_mark_unstable(struct clocksource *cs) { } 746 747 static inline void clocksource_watchdog_lock(unsigned long *flags) { } 748 static inline void clocksource_watchdog_unlock(unsigned long *flags) { } 749 750 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */ 751 752 static bool clocksource_is_suspend(struct clocksource *cs) 753 { 754 return cs == suspend_clocksource; 755 } 756 757 static void __clocksource_suspend_select(struct clocksource *cs) 758 { 759 /* 760 * Skip the clocksource which will be stopped in suspend state. 761 */ 762 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP)) 763 return; 764 765 /* 766 * The nonstop clocksource can be selected as the suspend clocksource to 767 * calculate the suspend time, so it should not supply suspend/resume 768 * interfaces to suspend the nonstop clocksource when system suspends. 769 */ 770 if (cs->suspend || cs->resume) { 771 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n", 772 cs->name); 773 } 774 775 /* Pick the best rating. */ 776 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating) 777 suspend_clocksource = cs; 778 } 779 780 /** 781 * clocksource_suspend_select - Select the best clocksource for suspend timing 782 * @fallback: if select a fallback clocksource 783 */ 784 static void clocksource_suspend_select(bool fallback) 785 { 786 struct clocksource *cs, *old_suspend; 787 788 old_suspend = suspend_clocksource; 789 if (fallback) 790 suspend_clocksource = NULL; 791 792 list_for_each_entry(cs, &clocksource_list, list) { 793 /* Skip current if we were requested for a fallback. */ 794 if (fallback && cs == old_suspend) 795 continue; 796 797 __clocksource_suspend_select(cs); 798 } 799 } 800 801 /** 802 * clocksource_start_suspend_timing - Start measuring the suspend timing 803 * @cs: current clocksource from timekeeping 804 * @start_cycles: current cycles from timekeeping 805 * 806 * This function will save the start cycle values of suspend timer to calculate 807 * the suspend time when resuming system. 808 * 809 * This function is called late in the suspend process from timekeeping_suspend(), 810 * that means processes are frozen, non-boot cpus and interrupts are disabled 811 * now. It is therefore possible to start the suspend timer without taking the 812 * clocksource mutex. 813 */ 814 void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles) 815 { 816 if (!suspend_clocksource) 817 return; 818 819 /* 820 * If current clocksource is the suspend timer, we should use the 821 * tkr_mono.cycle_last value as suspend_start to avoid same reading 822 * from suspend timer. 823 */ 824 if (clocksource_is_suspend(cs)) { 825 suspend_start = start_cycles; 826 return; 827 } 828 829 if (suspend_clocksource->enable && 830 suspend_clocksource->enable(suspend_clocksource)) { 831 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n"); 832 return; 833 } 834 835 suspend_start = suspend_clocksource->read(suspend_clocksource); 836 } 837 838 /** 839 * clocksource_stop_suspend_timing - Stop measuring the suspend timing 840 * @cs: current clocksource from timekeeping 841 * @cycle_now: current cycles from timekeeping 842 * 843 * This function will calculate the suspend time from suspend timer. 844 * 845 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource. 846 * 847 * This function is called early in the resume process from timekeeping_resume(), 848 * that means there is only one cpu, no processes are running and the interrupts 849 * are disabled. It is therefore possible to stop the suspend timer without 850 * taking the clocksource mutex. 851 */ 852 u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now) 853 { 854 u64 now, nsec = 0; 855 856 if (!suspend_clocksource) 857 return 0; 858 859 /* 860 * If current clocksource is the suspend timer, we should use the 861 * tkr_mono.cycle_last value from timekeeping as current cycle to 862 * avoid same reading from suspend timer. 863 */ 864 if (clocksource_is_suspend(cs)) 865 now = cycle_now; 866 else 867 now = suspend_clocksource->read(suspend_clocksource); 868 869 if (now > suspend_start) 870 nsec = cycles_to_nsec_safe(suspend_clocksource, suspend_start, now); 871 872 /* 873 * Disable the suspend timer to save power if current clocksource is 874 * not the suspend timer. 875 */ 876 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable) 877 suspend_clocksource->disable(suspend_clocksource); 878 879 return nsec; 880 } 881 882 /** 883 * clocksource_suspend - suspend the clocksource(s) 884 */ 885 void clocksource_suspend(void) 886 { 887 struct clocksource *cs; 888 889 list_for_each_entry_reverse(cs, &clocksource_list, list) 890 if (cs->suspend) 891 cs->suspend(cs); 892 } 893 894 /** 895 * clocksource_resume - resume the clocksource(s) 896 */ 897 void clocksource_resume(void) 898 { 899 struct clocksource *cs; 900 901 list_for_each_entry(cs, &clocksource_list, list) 902 if (cs->resume) 903 cs->resume(cs); 904 905 clocksource_resume_watchdog(); 906 } 907 908 /** 909 * clocksource_touch_watchdog - Update watchdog 910 * 911 * Update the watchdog after exception contexts such as kgdb so as not 912 * to incorrectly trip the watchdog. This might fail when the kernel 913 * was stopped in code which holds watchdog_lock. 914 */ 915 void clocksource_touch_watchdog(void) 916 { 917 clocksource_resume_watchdog(); 918 } 919 920 /** 921 * clocksource_max_adjustment- Returns max adjustment amount 922 * @cs: Pointer to clocksource 923 * 924 */ 925 static u32 clocksource_max_adjustment(struct clocksource *cs) 926 { 927 u64 ret; 928 /* 929 * We won't try to correct for more than 11% adjustments (110,000 ppm), 930 */ 931 ret = (u64)cs->mult * 11; 932 do_div(ret,100); 933 return (u32)ret; 934 } 935 936 /** 937 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted 938 * @mult: cycle to nanosecond multiplier 939 * @shift: cycle to nanosecond divisor (power of two) 940 * @maxadj: maximum adjustment value to mult (~11%) 941 * @mask: bitmask for two's complement subtraction of non 64 bit counters 942 * @max_cyc: maximum cycle value before potential overflow (does not include 943 * any safety margin) 944 * 945 * NOTE: This function includes a safety margin of 50%, in other words, we 946 * return half the number of nanoseconds the hardware counter can technically 947 * cover. This is done so that we can potentially detect problems caused by 948 * delayed timers or bad hardware, which might result in time intervals that 949 * are larger than what the math used can handle without overflows. 950 */ 951 u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc) 952 { 953 u64 max_nsecs, max_cycles; 954 955 /* 956 * Calculate the maximum number of cycles that we can pass to the 957 * cyc2ns() function without overflowing a 64-bit result. 958 */ 959 max_cycles = ULLONG_MAX; 960 do_div(max_cycles, mult+maxadj); 961 962 /* 963 * The actual maximum number of cycles we can defer the clocksource is 964 * determined by the minimum of max_cycles and mask. 965 * Note: Here we subtract the maxadj to make sure we don't sleep for 966 * too long if there's a large negative adjustment. 967 */ 968 max_cycles = min(max_cycles, mask); 969 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift); 970 971 /* return the max_cycles value as well if requested */ 972 if (max_cyc) 973 *max_cyc = max_cycles; 974 975 /* Return 50% of the actual maximum, so we can detect bad values */ 976 max_nsecs >>= 1; 977 978 return max_nsecs; 979 } 980 981 /** 982 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles 983 * @cs: Pointer to clocksource to be updated 984 * 985 */ 986 static inline void clocksource_update_max_deferment(struct clocksource *cs) 987 { 988 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift, 989 cs->maxadj, cs->mask, 990 &cs->max_cycles); 991 992 /* 993 * Threshold for detecting negative motion in clocksource_delta(). 994 * 995 * Allow for 0.875 of the counter width so that overly long idle 996 * sleeps, which go slightly over mask/2, do not trigger the 997 * negative motion detection. 998 */ 999 cs->max_raw_delta = (cs->mask >> 1) + (cs->mask >> 2) + (cs->mask >> 3); 1000 } 1001 1002 static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur) 1003 { 1004 struct clocksource *cs; 1005 1006 if (!finished_booting || list_empty(&clocksource_list)) 1007 return NULL; 1008 1009 /* 1010 * We pick the clocksource with the highest rating. If oneshot 1011 * mode is active, we pick the highres valid clocksource with 1012 * the best rating. 1013 */ 1014 list_for_each_entry(cs, &clocksource_list, list) { 1015 if (skipcur && cs == curr_clocksource) 1016 continue; 1017 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 1018 continue; 1019 return cs; 1020 } 1021 return NULL; 1022 } 1023 1024 static void __clocksource_select(bool skipcur) 1025 { 1026 bool oneshot = tick_oneshot_mode_active(); 1027 struct clocksource *best, *cs; 1028 1029 /* Find the best suitable clocksource */ 1030 best = clocksource_find_best(oneshot, skipcur); 1031 if (!best) 1032 return; 1033 1034 if (!strlen(override_name)) 1035 goto found; 1036 1037 /* Check for the override clocksource. */ 1038 list_for_each_entry(cs, &clocksource_list, list) { 1039 if (skipcur && cs == curr_clocksource) 1040 continue; 1041 if (strcmp(cs->name, override_name) != 0) 1042 continue; 1043 /* 1044 * Check to make sure we don't switch to a non-highres 1045 * capable clocksource if the tick code is in oneshot 1046 * mode (highres or nohz) 1047 */ 1048 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) { 1049 /* Override clocksource cannot be used. */ 1050 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 1051 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n", 1052 cs->name); 1053 override_name[0] = 0; 1054 } else { 1055 /* 1056 * The override cannot be currently verified. 1057 * Deferring to let the watchdog check. 1058 */ 1059 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n", 1060 cs->name); 1061 } 1062 } else 1063 /* Override clocksource can be used. */ 1064 best = cs; 1065 break; 1066 } 1067 1068 found: 1069 if (curr_clocksource != best && !timekeeping_notify(best)) { 1070 pr_info("Switched to clocksource %s\n", best->name); 1071 curr_clocksource = best; 1072 } 1073 } 1074 1075 /** 1076 * clocksource_select - Select the best clocksource available 1077 * 1078 * Private function. Must hold clocksource_mutex when called. 1079 * 1080 * Select the clocksource with the best rating, or the clocksource, 1081 * which is selected by userspace override. 1082 */ 1083 static void clocksource_select(void) 1084 { 1085 __clocksource_select(false); 1086 } 1087 1088 static void clocksource_select_fallback(void) 1089 { 1090 __clocksource_select(true); 1091 } 1092 1093 /* 1094 * clocksource_done_booting - Called near the end of core bootup 1095 * 1096 * Hack to avoid lots of clocksource churn at boot time. 1097 * We use fs_initcall because we want this to start before 1098 * device_initcall but after subsys_initcall. 1099 */ 1100 static int __init clocksource_done_booting(void) 1101 { 1102 mutex_lock(&clocksource_mutex); 1103 curr_clocksource = clocksource_default_clock(); 1104 finished_booting = 1; 1105 /* 1106 * Run the watchdog first to eliminate unstable clock sources 1107 */ 1108 __clocksource_watchdog_kthread(); 1109 clocksource_select(); 1110 mutex_unlock(&clocksource_mutex); 1111 return 0; 1112 } 1113 fs_initcall(clocksource_done_booting); 1114 1115 /* 1116 * Enqueue the clocksource sorted by rating 1117 */ 1118 static void clocksource_enqueue(struct clocksource *cs) 1119 { 1120 struct list_head *entry = &clocksource_list; 1121 struct clocksource *tmp; 1122 1123 list_for_each_entry(tmp, &clocksource_list, list) { 1124 /* Keep track of the place, where to insert */ 1125 if (tmp->rating < cs->rating) 1126 break; 1127 entry = &tmp->list; 1128 } 1129 list_add(&cs->list, entry); 1130 } 1131 1132 /** 1133 * __clocksource_update_freq_scale - Used update clocksource with new freq 1134 * @cs: clocksource to be registered 1135 * @scale: Scale factor multiplied against freq to get clocksource hz 1136 * @freq: clocksource frequency (cycles per second) divided by scale 1137 * 1138 * This should only be called from the clocksource->enable() method. 1139 * 1140 * This *SHOULD NOT* be called directly! Please use the 1141 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper 1142 * functions. 1143 */ 1144 void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq) 1145 { 1146 u64 sec; 1147 1148 /* 1149 * Default clocksources are *special* and self-define their mult/shift. 1150 * But, you're not special, so you should specify a freq value. 1151 */ 1152 if (freq) { 1153 /* 1154 * Calc the maximum number of seconds which we can run before 1155 * wrapping around. For clocksources which have a mask > 32-bit 1156 * we need to limit the max sleep time to have a good 1157 * conversion precision. 10 minutes is still a reasonable 1158 * amount. That results in a shift value of 24 for a 1159 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to 1160 * ~ 0.06ppm granularity for NTP. 1161 */ 1162 sec = cs->mask; 1163 do_div(sec, freq); 1164 do_div(sec, scale); 1165 if (!sec) 1166 sec = 1; 1167 else if (sec > 600 && cs->mask > UINT_MAX) 1168 sec = 600; 1169 1170 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq, 1171 NSEC_PER_SEC / scale, sec * scale); 1172 } 1173 1174 /* 1175 * If the uncertainty margin is not specified, calculate it. If 1176 * both scale and freq are non-zero, calculate the clock period, but 1177 * bound below at 2*WATCHDOG_MAX_SKEW, that is, 500ppm by default. 1178 * However, if either of scale or freq is zero, be very conservative 1179 * and take the tens-of-milliseconds WATCHDOG_THRESHOLD value 1180 * for the uncertainty margin. Allow stupidly small uncertainty 1181 * margins to be specified by the caller for testing purposes, 1182 * but warn to discourage production use of this capability. 1183 * 1184 * Bottom line: The sum of the uncertainty margins of the 1185 * watchdog clocksource and the clocksource under test will be at 1186 * least 500ppm by default. For more information, please see the 1187 * comment preceding CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US above. 1188 */ 1189 if (scale && freq && !cs->uncertainty_margin) { 1190 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq); 1191 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW) 1192 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW; 1193 } else if (!cs->uncertainty_margin) { 1194 cs->uncertainty_margin = WATCHDOG_THRESHOLD; 1195 } 1196 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW); 1197 1198 /* 1199 * Ensure clocksources that have large 'mult' values don't overflow 1200 * when adjusted. 1201 */ 1202 cs->maxadj = clocksource_max_adjustment(cs); 1203 while (freq && ((cs->mult + cs->maxadj < cs->mult) 1204 || (cs->mult - cs->maxadj > cs->mult))) { 1205 cs->mult >>= 1; 1206 cs->shift--; 1207 cs->maxadj = clocksource_max_adjustment(cs); 1208 } 1209 1210 /* 1211 * Only warn for *special* clocksources that self-define 1212 * their mult/shift values and don't specify a freq. 1213 */ 1214 WARN_ONCE(cs->mult + cs->maxadj < cs->mult, 1215 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n", 1216 cs->name); 1217 1218 clocksource_update_max_deferment(cs); 1219 1220 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n", 1221 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns); 1222 } 1223 EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale); 1224 1225 /** 1226 * __clocksource_register_scale - Used to install new clocksources 1227 * @cs: clocksource to be registered 1228 * @scale: Scale factor multiplied against freq to get clocksource hz 1229 * @freq: clocksource frequency (cycles per second) divided by scale 1230 * 1231 * Returns -EBUSY if registration fails, zero otherwise. 1232 * 1233 * This *SHOULD NOT* be called directly! Please use the 1234 * clocksource_register_hz() or clocksource_register_khz helper functions. 1235 */ 1236 int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq) 1237 { 1238 unsigned long flags; 1239 1240 clocksource_arch_init(cs); 1241 1242 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX)) 1243 cs->id = CSID_GENERIC; 1244 if (cs->vdso_clock_mode < 0 || 1245 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) { 1246 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n", 1247 cs->name, cs->vdso_clock_mode); 1248 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE; 1249 } 1250 1251 /* Initialize mult/shift and max_idle_ns */ 1252 __clocksource_update_freq_scale(cs, scale, freq); 1253 1254 /* Add clocksource to the clocksource list */ 1255 mutex_lock(&clocksource_mutex); 1256 1257 clocksource_watchdog_lock(&flags); 1258 clocksource_enqueue(cs); 1259 clocksource_enqueue_watchdog(cs); 1260 clocksource_watchdog_unlock(&flags); 1261 1262 clocksource_select(); 1263 clocksource_select_watchdog(false); 1264 __clocksource_suspend_select(cs); 1265 mutex_unlock(&clocksource_mutex); 1266 return 0; 1267 } 1268 EXPORT_SYMBOL_GPL(__clocksource_register_scale); 1269 1270 /* 1271 * Unbind clocksource @cs. Called with clocksource_mutex held 1272 */ 1273 static int clocksource_unbind(struct clocksource *cs) 1274 { 1275 unsigned long flags; 1276 1277 if (clocksource_is_watchdog(cs)) { 1278 /* Select and try to install a replacement watchdog. */ 1279 clocksource_select_watchdog(true); 1280 if (clocksource_is_watchdog(cs)) 1281 return -EBUSY; 1282 } 1283 1284 if (cs == curr_clocksource) { 1285 /* Select and try to install a replacement clock source */ 1286 clocksource_select_fallback(); 1287 if (curr_clocksource == cs) 1288 return -EBUSY; 1289 } 1290 1291 if (clocksource_is_suspend(cs)) { 1292 /* 1293 * Select and try to install a replacement suspend clocksource. 1294 * If no replacement suspend clocksource, we will just let the 1295 * clocksource go and have no suspend clocksource. 1296 */ 1297 clocksource_suspend_select(true); 1298 } 1299 1300 clocksource_watchdog_lock(&flags); 1301 clocksource_dequeue_watchdog(cs); 1302 list_del_init(&cs->list); 1303 clocksource_watchdog_unlock(&flags); 1304 1305 return 0; 1306 } 1307 1308 /** 1309 * clocksource_unregister - remove a registered clocksource 1310 * @cs: clocksource to be unregistered 1311 */ 1312 int clocksource_unregister(struct clocksource *cs) 1313 { 1314 int ret = 0; 1315 1316 mutex_lock(&clocksource_mutex); 1317 if (!list_empty(&cs->list)) 1318 ret = clocksource_unbind(cs); 1319 mutex_unlock(&clocksource_mutex); 1320 return ret; 1321 } 1322 EXPORT_SYMBOL(clocksource_unregister); 1323 1324 #ifdef CONFIG_SYSFS 1325 /** 1326 * current_clocksource_show - sysfs interface for current clocksource 1327 * @dev: unused 1328 * @attr: unused 1329 * @buf: char buffer to be filled with clocksource list 1330 * 1331 * Provides sysfs interface for listing current clocksource. 1332 */ 1333 static ssize_t current_clocksource_show(struct device *dev, 1334 struct device_attribute *attr, 1335 char *buf) 1336 { 1337 ssize_t count = 0; 1338 1339 mutex_lock(&clocksource_mutex); 1340 count = sysfs_emit(buf, "%s\n", curr_clocksource->name); 1341 mutex_unlock(&clocksource_mutex); 1342 1343 return count; 1344 } 1345 1346 ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt) 1347 { 1348 size_t ret = cnt; 1349 1350 /* strings from sysfs write are not 0 terminated! */ 1351 if (!cnt || cnt >= CS_NAME_LEN) 1352 return -EINVAL; 1353 1354 /* strip of \n: */ 1355 if (buf[cnt-1] == '\n') 1356 cnt--; 1357 if (cnt > 0) 1358 memcpy(dst, buf, cnt); 1359 dst[cnt] = 0; 1360 return ret; 1361 } 1362 1363 /** 1364 * current_clocksource_store - interface for manually overriding clocksource 1365 * @dev: unused 1366 * @attr: unused 1367 * @buf: name of override clocksource 1368 * @count: length of buffer 1369 * 1370 * Takes input from sysfs interface for manually overriding the default 1371 * clocksource selection. 1372 */ 1373 static ssize_t current_clocksource_store(struct device *dev, 1374 struct device_attribute *attr, 1375 const char *buf, size_t count) 1376 { 1377 ssize_t ret; 1378 1379 mutex_lock(&clocksource_mutex); 1380 1381 ret = sysfs_get_uname(buf, override_name, count); 1382 if (ret >= 0) 1383 clocksource_select(); 1384 1385 mutex_unlock(&clocksource_mutex); 1386 1387 return ret; 1388 } 1389 static DEVICE_ATTR_RW(current_clocksource); 1390 1391 /** 1392 * unbind_clocksource_store - interface for manually unbinding clocksource 1393 * @dev: unused 1394 * @attr: unused 1395 * @buf: unused 1396 * @count: length of buffer 1397 * 1398 * Takes input from sysfs interface for manually unbinding a clocksource. 1399 */ 1400 static ssize_t unbind_clocksource_store(struct device *dev, 1401 struct device_attribute *attr, 1402 const char *buf, size_t count) 1403 { 1404 struct clocksource *cs; 1405 char name[CS_NAME_LEN]; 1406 ssize_t ret; 1407 1408 ret = sysfs_get_uname(buf, name, count); 1409 if (ret < 0) 1410 return ret; 1411 1412 ret = -ENODEV; 1413 mutex_lock(&clocksource_mutex); 1414 list_for_each_entry(cs, &clocksource_list, list) { 1415 if (strcmp(cs->name, name)) 1416 continue; 1417 ret = clocksource_unbind(cs); 1418 break; 1419 } 1420 mutex_unlock(&clocksource_mutex); 1421 1422 return ret ? ret : count; 1423 } 1424 static DEVICE_ATTR_WO(unbind_clocksource); 1425 1426 /** 1427 * available_clocksource_show - sysfs interface for listing clocksource 1428 * @dev: unused 1429 * @attr: unused 1430 * @buf: char buffer to be filled with clocksource list 1431 * 1432 * Provides sysfs interface for listing registered clocksources 1433 */ 1434 static ssize_t available_clocksource_show(struct device *dev, 1435 struct device_attribute *attr, 1436 char *buf) 1437 { 1438 struct clocksource *src; 1439 ssize_t count = 0; 1440 1441 mutex_lock(&clocksource_mutex); 1442 list_for_each_entry(src, &clocksource_list, list) { 1443 /* 1444 * Don't show non-HRES clocksource if the tick code is 1445 * in one shot mode (highres=on or nohz=on) 1446 */ 1447 if (!tick_oneshot_mode_active() || 1448 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 1449 count += snprintf(buf + count, 1450 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), 1451 "%s ", src->name); 1452 } 1453 mutex_unlock(&clocksource_mutex); 1454 1455 count += snprintf(buf + count, 1456 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n"); 1457 1458 return count; 1459 } 1460 static DEVICE_ATTR_RO(available_clocksource); 1461 1462 static struct attribute *clocksource_attrs[] = { 1463 &dev_attr_current_clocksource.attr, 1464 &dev_attr_unbind_clocksource.attr, 1465 &dev_attr_available_clocksource.attr, 1466 NULL 1467 }; 1468 ATTRIBUTE_GROUPS(clocksource); 1469 1470 static const struct bus_type clocksource_subsys = { 1471 .name = "clocksource", 1472 .dev_name = "clocksource", 1473 }; 1474 1475 static struct device device_clocksource = { 1476 .id = 0, 1477 .bus = &clocksource_subsys, 1478 .groups = clocksource_groups, 1479 }; 1480 1481 static int __init init_clocksource_sysfs(void) 1482 { 1483 int error = subsys_system_register(&clocksource_subsys, NULL); 1484 1485 if (!error) 1486 error = device_register(&device_clocksource); 1487 1488 return error; 1489 } 1490 1491 device_initcall(init_clocksource_sysfs); 1492 #endif /* CONFIG_SYSFS */ 1493 1494 /** 1495 * boot_override_clocksource - boot clock override 1496 * @str: override name 1497 * 1498 * Takes a clocksource= boot argument and uses it 1499 * as the clocksource override name. 1500 */ 1501 static int __init boot_override_clocksource(char* str) 1502 { 1503 mutex_lock(&clocksource_mutex); 1504 if (str) 1505 strscpy(override_name, str); 1506 mutex_unlock(&clocksource_mutex); 1507 return 1; 1508 } 1509 1510 __setup("clocksource=", boot_override_clocksource); 1511 1512 /** 1513 * boot_override_clock - Compatibility layer for deprecated boot option 1514 * @str: override name 1515 * 1516 * DEPRECATED! Takes a clock= boot argument and uses it 1517 * as the clocksource override name 1518 */ 1519 static int __init boot_override_clock(char* str) 1520 { 1521 if (!strcmp(str, "pmtmr")) { 1522 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n"); 1523 return boot_override_clocksource("acpi_pm"); 1524 } 1525 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n"); 1526 return boot_override_clocksource(str); 1527 } 1528 1529 __setup("clock=", boot_override_clock); 1530