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