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 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 || 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_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 migrate_disable(); 377 clocksource_verify_choose_cpus(); 378 if (cpumask_empty(&cpus_chosen)) { 379 migrate_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_info("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", 386 cs->name, testcpu, cpumask_pr_args(&cpus_chosen)); 387 preempt_disable(); 388 for_each_cpu(cpu, &cpus_chosen) { 389 if (cpu == testcpu) 390 continue; 391 csnow_begin = cs->read(cs); 392 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1); 393 csnow_end = cs->read(cs); 394 delta = (s64)((csnow_mid - csnow_begin) & cs->mask); 395 if (delta < 0) 396 cpumask_set_cpu(cpu, &cpus_behind); 397 delta = (csnow_end - csnow_mid) & cs->mask; 398 if (delta < 0) 399 cpumask_set_cpu(cpu, &cpus_ahead); 400 cs_nsec = cycles_to_nsec_safe(cs, csnow_begin, csnow_end); 401 if (cs_nsec > cs_nsec_max) 402 cs_nsec_max = cs_nsec; 403 if (cs_nsec < cs_nsec_min) 404 cs_nsec_min = cs_nsec; 405 } 406 preempt_enable(); 407 migrate_enable(); 408 cpus_read_unlock(); 409 if (!cpumask_empty(&cpus_ahead)) 410 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n", 411 cpumask_pr_args(&cpus_ahead), testcpu, cs->name); 412 if (!cpumask_empty(&cpus_behind)) 413 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n", 414 cpumask_pr_args(&cpus_behind), testcpu, cs->name); 415 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind)) 416 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n", 417 testcpu, cs_nsec_min, cs_nsec_max, cs->name); 418 } 419 EXPORT_SYMBOL_GPL(clocksource_verify_percpu); 420 421 static inline void clocksource_reset_watchdog(void) 422 { 423 struct clocksource *cs; 424 425 list_for_each_entry(cs, &watchdog_list, wd_list) 426 cs->flags &= ~CLOCK_SOURCE_WATCHDOG; 427 } 428 429 430 static void clocksource_watchdog(struct timer_list *unused) 431 { 432 int64_t wd_nsec, cs_nsec, interval; 433 u64 csnow, wdnow, cslast, wdlast; 434 int next_cpu, reset_pending; 435 struct clocksource *cs; 436 enum wd_read_status read_ret; 437 unsigned long extra_wait = 0; 438 u32 md; 439 440 spin_lock(&watchdog_lock); 441 if (!watchdog_running) 442 goto out; 443 444 reset_pending = atomic_read(&watchdog_reset_pending); 445 446 list_for_each_entry(cs, &watchdog_list, wd_list) { 447 448 /* Clocksource already marked unstable? */ 449 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 450 if (finished_booting) 451 schedule_work(&watchdog_work); 452 continue; 453 } 454 455 read_ret = cs_watchdog_read(cs, &csnow, &wdnow); 456 457 if (read_ret == WD_READ_UNSTABLE) { 458 /* Clock readout unreliable, so give it up. */ 459 __clocksource_unstable(cs); 460 continue; 461 } 462 463 /* 464 * When WD_READ_SKIP is returned, it means the system is likely 465 * under very heavy load, where the latency of reading 466 * watchdog/clocksource is very big, and affect the accuracy of 467 * watchdog check. So give system some space and suspend the 468 * watchdog check for 5 minutes. 469 */ 470 if (read_ret == WD_READ_SKIP) { 471 /* 472 * As the watchdog timer will be suspended, and 473 * cs->last could keep unchanged for 5 minutes, reset 474 * the counters. 475 */ 476 clocksource_reset_watchdog(); 477 extra_wait = HZ * 300; 478 break; 479 } 480 481 /* Clocksource initialized ? */ 482 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) || 483 atomic_read(&watchdog_reset_pending)) { 484 cs->flags |= CLOCK_SOURCE_WATCHDOG; 485 cs->wd_last = wdnow; 486 cs->cs_last = csnow; 487 continue; 488 } 489 490 wd_nsec = cycles_to_nsec_safe(watchdog, cs->wd_last, wdnow); 491 cs_nsec = cycles_to_nsec_safe(cs, cs->cs_last, csnow); 492 wdlast = cs->wd_last; /* save these in case we print them */ 493 cslast = cs->cs_last; 494 cs->cs_last = csnow; 495 cs->wd_last = wdnow; 496 497 if (atomic_read(&watchdog_reset_pending)) 498 continue; 499 500 /* 501 * The processing of timer softirqs can get delayed (usually 502 * on account of ksoftirqd not getting to run in a timely 503 * manner), which causes the watchdog interval to stretch. 504 * Skew detection may fail for longer watchdog intervals 505 * on account of fixed margins being used. 506 * Some clocksources, e.g. acpi_pm, cannot tolerate 507 * watchdog intervals longer than a few seconds. 508 */ 509 interval = max(cs_nsec, wd_nsec); 510 if (unlikely(interval > WATCHDOG_INTERVAL_MAX_NS)) { 511 if (system_state > SYSTEM_SCHEDULING && 512 interval > 2 * watchdog_max_interval) { 513 watchdog_max_interval = interval; 514 pr_warn("Long readout interval, skipping watchdog check: cs_nsec: %lld wd_nsec: %lld\n", 515 cs_nsec, wd_nsec); 516 } 517 watchdog_timer.expires = jiffies; 518 continue; 519 } 520 521 /* Check the deviation from the watchdog clocksource. */ 522 md = cs->uncertainty_margin + watchdog->uncertainty_margin; 523 if (abs(cs_nsec - wd_nsec) > md) { 524 s64 cs_wd_msec; 525 s64 wd_msec; 526 u32 wd_rem; 527 528 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n", 529 smp_processor_id(), cs->name); 530 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n", 531 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask); 532 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n", 533 cs->name, cs_nsec, csnow, cslast, cs->mask); 534 cs_wd_msec = div_s64_rem(cs_nsec - wd_nsec, 1000 * 1000, &wd_rem); 535 wd_msec = div_s64_rem(wd_nsec, 1000 * 1000, &wd_rem); 536 pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n", 537 cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec); 538 if (curr_clocksource == cs) 539 pr_warn(" '%s' is current clocksource.\n", cs->name); 540 else if (curr_clocksource) 541 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name); 542 else 543 pr_warn(" No current clocksource.\n"); 544 __clocksource_unstable(cs); 545 continue; 546 } 547 548 if (cs == curr_clocksource && cs->tick_stable) 549 cs->tick_stable(cs); 550 551 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && 552 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) && 553 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) { 554 /* Mark it valid for high-res. */ 555 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 556 557 /* 558 * clocksource_done_booting() will sort it if 559 * finished_booting is not set yet. 560 */ 561 if (!finished_booting) 562 continue; 563 564 /* 565 * If this is not the current clocksource let 566 * the watchdog thread reselect it. Due to the 567 * change to high res this clocksource might 568 * be preferred now. If it is the current 569 * clocksource let the tick code know about 570 * that change. 571 */ 572 if (cs != curr_clocksource) { 573 cs->flags |= CLOCK_SOURCE_RESELECT; 574 schedule_work(&watchdog_work); 575 } else { 576 tick_clock_notify(); 577 } 578 } 579 } 580 581 /* 582 * We only clear the watchdog_reset_pending, when we did a 583 * full cycle through all clocksources. 584 */ 585 if (reset_pending) 586 atomic_dec(&watchdog_reset_pending); 587 588 /* 589 * Cycle through CPUs to check if the CPUs stay synchronized 590 * to each other. 591 */ 592 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask); 593 if (next_cpu >= nr_cpu_ids) 594 next_cpu = cpumask_first(cpu_online_mask); 595 596 /* 597 * Arm timer if not already pending: could race with concurrent 598 * pair clocksource_stop_watchdog() clocksource_start_watchdog(). 599 */ 600 if (!timer_pending(&watchdog_timer)) { 601 watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait; 602 add_timer_on(&watchdog_timer, next_cpu); 603 } 604 out: 605 spin_unlock(&watchdog_lock); 606 } 607 608 static inline void clocksource_start_watchdog(void) 609 { 610 if (watchdog_running || !watchdog || list_empty(&watchdog_list)) 611 return; 612 timer_setup(&watchdog_timer, clocksource_watchdog, 0); 613 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL; 614 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask)); 615 watchdog_running = 1; 616 } 617 618 static inline void clocksource_stop_watchdog(void) 619 { 620 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list))) 621 return; 622 timer_delete(&watchdog_timer); 623 watchdog_running = 0; 624 } 625 626 static void clocksource_resume_watchdog(void) 627 { 628 atomic_inc(&watchdog_reset_pending); 629 } 630 631 static void clocksource_enqueue_watchdog(struct clocksource *cs) 632 { 633 INIT_LIST_HEAD(&cs->wd_list); 634 635 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { 636 /* cs is a clocksource to be watched. */ 637 list_add(&cs->wd_list, &watchdog_list); 638 cs->flags &= ~CLOCK_SOURCE_WATCHDOG; 639 } else { 640 /* cs is a watchdog. */ 641 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 642 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 643 } 644 } 645 646 static void clocksource_select_watchdog(bool fallback) 647 { 648 struct clocksource *cs, *old_wd; 649 unsigned long flags; 650 651 spin_lock_irqsave(&watchdog_lock, flags); 652 /* save current watchdog */ 653 old_wd = watchdog; 654 if (fallback) 655 watchdog = NULL; 656 657 list_for_each_entry(cs, &clocksource_list, list) { 658 /* cs is a clocksource to be watched. */ 659 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) 660 continue; 661 662 /* Skip current if we were requested for a fallback. */ 663 if (fallback && cs == old_wd) 664 continue; 665 666 /* Pick the best watchdog. */ 667 if (!watchdog || cs->rating > watchdog->rating) 668 watchdog = cs; 669 } 670 /* If we failed to find a fallback restore the old one. */ 671 if (!watchdog) 672 watchdog = old_wd; 673 674 /* If we changed the watchdog we need to reset cycles. */ 675 if (watchdog != old_wd) 676 clocksource_reset_watchdog(); 677 678 /* Check if the watchdog timer needs to be started. */ 679 clocksource_start_watchdog(); 680 spin_unlock_irqrestore(&watchdog_lock, flags); 681 } 682 683 static void clocksource_dequeue_watchdog(struct clocksource *cs) 684 { 685 if (cs != watchdog) { 686 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { 687 /* cs is a watched clocksource. */ 688 list_del_init(&cs->wd_list); 689 /* Check if the watchdog timer needs to be stopped. */ 690 clocksource_stop_watchdog(); 691 } 692 } 693 } 694 695 static int __clocksource_watchdog_kthread(void) 696 { 697 struct clocksource *cs, *tmp; 698 unsigned long flags; 699 int select = 0; 700 701 /* Do any required per-CPU skew verification. */ 702 if (curr_clocksource && 703 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE && 704 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU) 705 clocksource_verify_percpu(curr_clocksource); 706 707 spin_lock_irqsave(&watchdog_lock, flags); 708 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) { 709 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 710 list_del_init(&cs->wd_list); 711 clocksource_change_rating(cs, 0); 712 select = 1; 713 } 714 if (cs->flags & CLOCK_SOURCE_RESELECT) { 715 cs->flags &= ~CLOCK_SOURCE_RESELECT; 716 select = 1; 717 } 718 } 719 /* Check if the watchdog timer needs to be stopped. */ 720 clocksource_stop_watchdog(); 721 spin_unlock_irqrestore(&watchdog_lock, flags); 722 723 return select; 724 } 725 726 static int clocksource_watchdog_kthread(void *data) 727 { 728 mutex_lock(&clocksource_mutex); 729 if (__clocksource_watchdog_kthread()) 730 clocksource_select(); 731 mutex_unlock(&clocksource_mutex); 732 return 0; 733 } 734 735 static bool clocksource_is_watchdog(struct clocksource *cs) 736 { 737 return cs == watchdog; 738 } 739 740 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */ 741 742 static void clocksource_enqueue_watchdog(struct clocksource *cs) 743 { 744 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 745 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 746 } 747 748 static void clocksource_select_watchdog(bool fallback) { } 749 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { } 750 static inline void clocksource_resume_watchdog(void) { } 751 static inline int __clocksource_watchdog_kthread(void) { return 0; } 752 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; } 753 void clocksource_mark_unstable(struct clocksource *cs) { } 754 755 static inline void clocksource_watchdog_lock(unsigned long *flags) { } 756 static inline void clocksource_watchdog_unlock(unsigned long *flags) { } 757 758 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */ 759 760 static bool clocksource_is_suspend(struct clocksource *cs) 761 { 762 return cs == suspend_clocksource; 763 } 764 765 static void __clocksource_suspend_select(struct clocksource *cs) 766 { 767 /* 768 * Skip the clocksource which will be stopped in suspend state. 769 */ 770 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP)) 771 return; 772 773 /* 774 * The nonstop clocksource can be selected as the suspend clocksource to 775 * calculate the suspend time, so it should not supply suspend/resume 776 * interfaces to suspend the nonstop clocksource when system suspends. 777 */ 778 if (cs->suspend || cs->resume) { 779 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n", 780 cs->name); 781 } 782 783 /* Pick the best rating. */ 784 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating) 785 suspend_clocksource = cs; 786 } 787 788 /** 789 * clocksource_suspend_select - Select the best clocksource for suspend timing 790 * @fallback: if select a fallback clocksource 791 */ 792 static void clocksource_suspend_select(bool fallback) 793 { 794 struct clocksource *cs, *old_suspend; 795 796 old_suspend = suspend_clocksource; 797 if (fallback) 798 suspend_clocksource = NULL; 799 800 list_for_each_entry(cs, &clocksource_list, list) { 801 /* Skip current if we were requested for a fallback. */ 802 if (fallback && cs == old_suspend) 803 continue; 804 805 __clocksource_suspend_select(cs); 806 } 807 } 808 809 /** 810 * clocksource_start_suspend_timing - Start measuring the suspend timing 811 * @cs: current clocksource from timekeeping 812 * @start_cycles: current cycles from timekeeping 813 * 814 * This function will save the start cycle values of suspend timer to calculate 815 * the suspend time when resuming system. 816 * 817 * This function is called late in the suspend process from timekeeping_suspend(), 818 * that means processes are frozen, non-boot cpus and interrupts are disabled 819 * now. It is therefore possible to start the suspend timer without taking the 820 * clocksource mutex. 821 */ 822 void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles) 823 { 824 if (!suspend_clocksource) 825 return; 826 827 /* 828 * If current clocksource is the suspend timer, we should use the 829 * tkr_mono.cycle_last value as suspend_start to avoid same reading 830 * from suspend timer. 831 */ 832 if (clocksource_is_suspend(cs)) { 833 suspend_start = start_cycles; 834 return; 835 } 836 837 if (suspend_clocksource->enable && 838 suspend_clocksource->enable(suspend_clocksource)) { 839 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n"); 840 return; 841 } 842 843 suspend_start = suspend_clocksource->read(suspend_clocksource); 844 } 845 846 /** 847 * clocksource_stop_suspend_timing - Stop measuring the suspend timing 848 * @cs: current clocksource from timekeeping 849 * @cycle_now: current cycles from timekeeping 850 * 851 * This function will calculate the suspend time from suspend timer. 852 * 853 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource. 854 * 855 * This function is called early in the resume process from timekeeping_resume(), 856 * that means there is only one cpu, no processes are running and the interrupts 857 * are disabled. It is therefore possible to stop the suspend timer without 858 * taking the clocksource mutex. 859 */ 860 u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now) 861 { 862 u64 now, nsec = 0; 863 864 if (!suspend_clocksource) 865 return 0; 866 867 /* 868 * If current clocksource is the suspend timer, we should use the 869 * tkr_mono.cycle_last value from timekeeping as current cycle to 870 * avoid same reading from suspend timer. 871 */ 872 if (clocksource_is_suspend(cs)) 873 now = cycle_now; 874 else 875 now = suspend_clocksource->read(suspend_clocksource); 876 877 if (now > suspend_start) 878 nsec = cycles_to_nsec_safe(suspend_clocksource, suspend_start, now); 879 880 /* 881 * Disable the suspend timer to save power if current clocksource is 882 * not the suspend timer. 883 */ 884 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable) 885 suspend_clocksource->disable(suspend_clocksource); 886 887 return nsec; 888 } 889 890 /** 891 * clocksource_suspend - suspend the clocksource(s) 892 */ 893 void clocksource_suspend(void) 894 { 895 struct clocksource *cs; 896 897 list_for_each_entry_reverse(cs, &clocksource_list, list) 898 if (cs->suspend) 899 cs->suspend(cs); 900 } 901 902 /** 903 * clocksource_resume - resume the clocksource(s) 904 */ 905 void clocksource_resume(void) 906 { 907 struct clocksource *cs; 908 909 list_for_each_entry(cs, &clocksource_list, list) 910 if (cs->resume) 911 cs->resume(cs); 912 913 clocksource_resume_watchdog(); 914 } 915 916 /** 917 * clocksource_touch_watchdog - Update watchdog 918 * 919 * Update the watchdog after exception contexts such as kgdb so as not 920 * to incorrectly trip the watchdog. This might fail when the kernel 921 * was stopped in code which holds watchdog_lock. 922 */ 923 void clocksource_touch_watchdog(void) 924 { 925 clocksource_resume_watchdog(); 926 } 927 928 /** 929 * clocksource_max_adjustment- Returns max adjustment amount 930 * @cs: Pointer to clocksource 931 * 932 */ 933 static u32 clocksource_max_adjustment(struct clocksource *cs) 934 { 935 u64 ret; 936 /* 937 * We won't try to correct for more than 11% adjustments (110,000 ppm), 938 */ 939 ret = (u64)cs->mult * 11; 940 do_div(ret,100); 941 return (u32)ret; 942 } 943 944 /** 945 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted 946 * @mult: cycle to nanosecond multiplier 947 * @shift: cycle to nanosecond divisor (power of two) 948 * @maxadj: maximum adjustment value to mult (~11%) 949 * @mask: bitmask for two's complement subtraction of non 64 bit counters 950 * @max_cyc: maximum cycle value before potential overflow (does not include 951 * any safety margin) 952 * 953 * NOTE: This function includes a safety margin of 50%, in other words, we 954 * return half the number of nanoseconds the hardware counter can technically 955 * cover. This is done so that we can potentially detect problems caused by 956 * delayed timers or bad hardware, which might result in time intervals that 957 * are larger than what the math used can handle without overflows. 958 */ 959 u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc) 960 { 961 u64 max_nsecs, max_cycles; 962 963 /* 964 * Calculate the maximum number of cycles that we can pass to the 965 * cyc2ns() function without overflowing a 64-bit result. 966 */ 967 max_cycles = ULLONG_MAX; 968 do_div(max_cycles, mult+maxadj); 969 970 /* 971 * The actual maximum number of cycles we can defer the clocksource is 972 * determined by the minimum of max_cycles and mask. 973 * Note: Here we subtract the maxadj to make sure we don't sleep for 974 * too long if there's a large negative adjustment. 975 */ 976 max_cycles = min(max_cycles, mask); 977 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift); 978 979 /* return the max_cycles value as well if requested */ 980 if (max_cyc) 981 *max_cyc = max_cycles; 982 983 /* Return 50% of the actual maximum, so we can detect bad values */ 984 max_nsecs >>= 1; 985 986 return max_nsecs; 987 } 988 989 /** 990 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles 991 * @cs: Pointer to clocksource to be updated 992 * 993 */ 994 static inline void clocksource_update_max_deferment(struct clocksource *cs) 995 { 996 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift, 997 cs->maxadj, cs->mask, 998 &cs->max_cycles); 999 1000 /* 1001 * Threshold for detecting negative motion in clocksource_delta(). 1002 * 1003 * Allow for 0.875 of the counter width so that overly long idle 1004 * sleeps, which go slightly over mask/2, do not trigger the 1005 * negative motion detection. 1006 */ 1007 cs->max_raw_delta = (cs->mask >> 1) + (cs->mask >> 2) + (cs->mask >> 3); 1008 } 1009 1010 static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur) 1011 { 1012 struct clocksource *cs; 1013 1014 if (!finished_booting || list_empty(&clocksource_list)) 1015 return NULL; 1016 1017 /* 1018 * We pick the clocksource with the highest rating. If oneshot 1019 * mode is active, we pick the highres valid clocksource with 1020 * the best rating. 1021 */ 1022 list_for_each_entry(cs, &clocksource_list, list) { 1023 if (skipcur && cs == curr_clocksource) 1024 continue; 1025 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 1026 continue; 1027 return cs; 1028 } 1029 return NULL; 1030 } 1031 1032 static void __clocksource_select(bool skipcur) 1033 { 1034 bool oneshot = tick_oneshot_mode_active(); 1035 struct clocksource *best, *cs; 1036 1037 /* Find the best suitable clocksource */ 1038 best = clocksource_find_best(oneshot, skipcur); 1039 if (!best) 1040 return; 1041 1042 if (!strlen(override_name)) 1043 goto found; 1044 1045 /* Check for the override clocksource. */ 1046 list_for_each_entry(cs, &clocksource_list, list) { 1047 if (skipcur && cs == curr_clocksource) 1048 continue; 1049 if (strcmp(cs->name, override_name) != 0) 1050 continue; 1051 /* 1052 * Check to make sure we don't switch to a non-highres 1053 * capable clocksource if the tick code is in oneshot 1054 * mode (highres or nohz) 1055 */ 1056 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) { 1057 /* Override clocksource cannot be used. */ 1058 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 1059 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n", 1060 cs->name); 1061 override_name[0] = 0; 1062 } else { 1063 /* 1064 * The override cannot be currently verified. 1065 * Deferring to let the watchdog check. 1066 */ 1067 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n", 1068 cs->name); 1069 } 1070 } else 1071 /* Override clocksource can be used. */ 1072 best = cs; 1073 break; 1074 } 1075 1076 found: 1077 if (curr_clocksource != best && !timekeeping_notify(best)) { 1078 pr_info("Switched to clocksource %s\n", best->name); 1079 curr_clocksource = best; 1080 } 1081 } 1082 1083 /** 1084 * clocksource_select - Select the best clocksource available 1085 * 1086 * Private function. Must hold clocksource_mutex when called. 1087 * 1088 * Select the clocksource with the best rating, or the clocksource, 1089 * which is selected by userspace override. 1090 */ 1091 static void clocksource_select(void) 1092 { 1093 __clocksource_select(false); 1094 } 1095 1096 static void clocksource_select_fallback(void) 1097 { 1098 __clocksource_select(true); 1099 } 1100 1101 /* 1102 * clocksource_done_booting - Called near the end of core bootup 1103 * 1104 * Hack to avoid lots of clocksource churn at boot time. 1105 * We use fs_initcall because we want this to start before 1106 * device_initcall but after subsys_initcall. 1107 */ 1108 static int __init clocksource_done_booting(void) 1109 { 1110 mutex_lock(&clocksource_mutex); 1111 curr_clocksource = clocksource_default_clock(); 1112 finished_booting = 1; 1113 /* 1114 * Run the watchdog first to eliminate unstable clock sources 1115 */ 1116 __clocksource_watchdog_kthread(); 1117 clocksource_select(); 1118 mutex_unlock(&clocksource_mutex); 1119 return 0; 1120 } 1121 fs_initcall(clocksource_done_booting); 1122 1123 /* 1124 * Enqueue the clocksource sorted by rating 1125 */ 1126 static void clocksource_enqueue(struct clocksource *cs) 1127 { 1128 struct list_head *entry = &clocksource_list; 1129 struct clocksource *tmp; 1130 1131 list_for_each_entry(tmp, &clocksource_list, list) { 1132 /* Keep track of the place, where to insert */ 1133 if (tmp->rating < cs->rating) 1134 break; 1135 entry = &tmp->list; 1136 } 1137 list_add(&cs->list, entry); 1138 } 1139 1140 /** 1141 * __clocksource_update_freq_scale - Used update clocksource with new freq 1142 * @cs: clocksource to be registered 1143 * @scale: Scale factor multiplied against freq to get clocksource hz 1144 * @freq: clocksource frequency (cycles per second) divided by scale 1145 * 1146 * This should only be called from the clocksource->enable() method. 1147 * 1148 * This *SHOULD NOT* be called directly! Please use the 1149 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper 1150 * functions. 1151 */ 1152 void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq) 1153 { 1154 u64 sec; 1155 1156 /* 1157 * Default clocksources are *special* and self-define their mult/shift. 1158 * But, you're not special, so you should specify a freq value. 1159 */ 1160 if (freq) { 1161 /* 1162 * Calc the maximum number of seconds which we can run before 1163 * wrapping around. For clocksources which have a mask > 32-bit 1164 * we need to limit the max sleep time to have a good 1165 * conversion precision. 10 minutes is still a reasonable 1166 * amount. That results in a shift value of 24 for a 1167 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to 1168 * ~ 0.06ppm granularity for NTP. 1169 */ 1170 sec = cs->mask; 1171 do_div(sec, freq); 1172 do_div(sec, scale); 1173 if (!sec) 1174 sec = 1; 1175 else if (sec > 600 && cs->mask > UINT_MAX) 1176 sec = 600; 1177 1178 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq, 1179 NSEC_PER_SEC / scale, sec * scale); 1180 } 1181 1182 /* 1183 * If the uncertainty margin is not specified, calculate it. If 1184 * both scale and freq are non-zero, calculate the clock period, but 1185 * bound below at 2*WATCHDOG_MAX_SKEW, that is, 500ppm by default. 1186 * However, if either of scale or freq is zero, be very conservative 1187 * and take the tens-of-milliseconds WATCHDOG_THRESHOLD value 1188 * for the uncertainty margin. Allow stupidly small uncertainty 1189 * margins to be specified by the caller for testing purposes, 1190 * but warn to discourage production use of this capability. 1191 * 1192 * Bottom line: The sum of the uncertainty margins of the 1193 * watchdog clocksource and the clocksource under test will be at 1194 * least 500ppm by default. For more information, please see the 1195 * comment preceding CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US above. 1196 */ 1197 if (scale && freq && !cs->uncertainty_margin) { 1198 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq); 1199 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW) 1200 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW; 1201 } else if (!cs->uncertainty_margin) { 1202 cs->uncertainty_margin = WATCHDOG_THRESHOLD; 1203 } 1204 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW); 1205 1206 /* 1207 * Ensure clocksources that have large 'mult' values don't overflow 1208 * when adjusted. 1209 */ 1210 cs->maxadj = clocksource_max_adjustment(cs); 1211 while (freq && ((cs->mult + cs->maxadj < cs->mult) 1212 || (cs->mult - cs->maxadj > cs->mult))) { 1213 cs->mult >>= 1; 1214 cs->shift--; 1215 cs->maxadj = clocksource_max_adjustment(cs); 1216 } 1217 1218 /* 1219 * Only warn for *special* clocksources that self-define 1220 * their mult/shift values and don't specify a freq. 1221 */ 1222 WARN_ONCE(cs->mult + cs->maxadj < cs->mult, 1223 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n", 1224 cs->name); 1225 1226 clocksource_update_max_deferment(cs); 1227 1228 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n", 1229 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns); 1230 } 1231 EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale); 1232 1233 /** 1234 * __clocksource_register_scale - Used to install new clocksources 1235 * @cs: clocksource to be registered 1236 * @scale: Scale factor multiplied against freq to get clocksource hz 1237 * @freq: clocksource frequency (cycles per second) divided by scale 1238 * 1239 * Returns -EBUSY if registration fails, zero otherwise. 1240 * 1241 * This *SHOULD NOT* be called directly! Please use the 1242 * clocksource_register_hz() or clocksource_register_khz helper functions. 1243 */ 1244 int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq) 1245 { 1246 unsigned long flags; 1247 1248 clocksource_arch_init(cs); 1249 1250 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX)) 1251 cs->id = CSID_GENERIC; 1252 if (cs->vdso_clock_mode < 0 || 1253 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) { 1254 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n", 1255 cs->name, cs->vdso_clock_mode); 1256 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE; 1257 } 1258 1259 /* Initialize mult/shift and max_idle_ns */ 1260 __clocksource_update_freq_scale(cs, scale, freq); 1261 1262 /* Add clocksource to the clocksource list */ 1263 mutex_lock(&clocksource_mutex); 1264 1265 clocksource_watchdog_lock(&flags); 1266 clocksource_enqueue(cs); 1267 clocksource_enqueue_watchdog(cs); 1268 clocksource_watchdog_unlock(&flags); 1269 1270 clocksource_select(); 1271 clocksource_select_watchdog(false); 1272 __clocksource_suspend_select(cs); 1273 mutex_unlock(&clocksource_mutex); 1274 return 0; 1275 } 1276 EXPORT_SYMBOL_GPL(__clocksource_register_scale); 1277 1278 /* 1279 * Unbind clocksource @cs. Called with clocksource_mutex held 1280 */ 1281 static int clocksource_unbind(struct clocksource *cs) 1282 { 1283 unsigned long flags; 1284 1285 if (clocksource_is_watchdog(cs)) { 1286 /* Select and try to install a replacement watchdog. */ 1287 clocksource_select_watchdog(true); 1288 if (clocksource_is_watchdog(cs)) 1289 return -EBUSY; 1290 } 1291 1292 if (cs == curr_clocksource) { 1293 /* Select and try to install a replacement clock source */ 1294 clocksource_select_fallback(); 1295 if (curr_clocksource == cs) 1296 return -EBUSY; 1297 } 1298 1299 if (clocksource_is_suspend(cs)) { 1300 /* 1301 * Select and try to install a replacement suspend clocksource. 1302 * If no replacement suspend clocksource, we will just let the 1303 * clocksource go and have no suspend clocksource. 1304 */ 1305 clocksource_suspend_select(true); 1306 } 1307 1308 clocksource_watchdog_lock(&flags); 1309 clocksource_dequeue_watchdog(cs); 1310 list_del_init(&cs->list); 1311 clocksource_watchdog_unlock(&flags); 1312 1313 return 0; 1314 } 1315 1316 /** 1317 * clocksource_unregister - remove a registered clocksource 1318 * @cs: clocksource to be unregistered 1319 */ 1320 int clocksource_unregister(struct clocksource *cs) 1321 { 1322 int ret = 0; 1323 1324 mutex_lock(&clocksource_mutex); 1325 if (!list_empty(&cs->list)) 1326 ret = clocksource_unbind(cs); 1327 mutex_unlock(&clocksource_mutex); 1328 return ret; 1329 } 1330 EXPORT_SYMBOL(clocksource_unregister); 1331 1332 #ifdef CONFIG_SYSFS 1333 /** 1334 * current_clocksource_show - sysfs interface for current clocksource 1335 * @dev: unused 1336 * @attr: unused 1337 * @buf: char buffer to be filled with clocksource list 1338 * 1339 * Provides sysfs interface for listing current clocksource. 1340 */ 1341 static ssize_t current_clocksource_show(struct device *dev, 1342 struct device_attribute *attr, 1343 char *buf) 1344 { 1345 ssize_t count = 0; 1346 1347 mutex_lock(&clocksource_mutex); 1348 count = sysfs_emit(buf, "%s\n", curr_clocksource->name); 1349 mutex_unlock(&clocksource_mutex); 1350 1351 return count; 1352 } 1353 1354 ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt) 1355 { 1356 size_t ret = cnt; 1357 1358 /* strings from sysfs write are not 0 terminated! */ 1359 if (!cnt || cnt >= CS_NAME_LEN) 1360 return -EINVAL; 1361 1362 /* strip of \n: */ 1363 if (buf[cnt-1] == '\n') 1364 cnt--; 1365 if (cnt > 0) 1366 memcpy(dst, buf, cnt); 1367 dst[cnt] = 0; 1368 return ret; 1369 } 1370 1371 /** 1372 * current_clocksource_store - interface for manually overriding clocksource 1373 * @dev: unused 1374 * @attr: unused 1375 * @buf: name of override clocksource 1376 * @count: length of buffer 1377 * 1378 * Takes input from sysfs interface for manually overriding the default 1379 * clocksource selection. 1380 */ 1381 static ssize_t current_clocksource_store(struct device *dev, 1382 struct device_attribute *attr, 1383 const char *buf, size_t count) 1384 { 1385 ssize_t ret; 1386 1387 mutex_lock(&clocksource_mutex); 1388 1389 ret = sysfs_get_uname(buf, override_name, count); 1390 if (ret >= 0) 1391 clocksource_select(); 1392 1393 mutex_unlock(&clocksource_mutex); 1394 1395 return ret; 1396 } 1397 static DEVICE_ATTR_RW(current_clocksource); 1398 1399 /** 1400 * unbind_clocksource_store - interface for manually unbinding clocksource 1401 * @dev: unused 1402 * @attr: unused 1403 * @buf: unused 1404 * @count: length of buffer 1405 * 1406 * Takes input from sysfs interface for manually unbinding a clocksource. 1407 */ 1408 static ssize_t unbind_clocksource_store(struct device *dev, 1409 struct device_attribute *attr, 1410 const char *buf, size_t count) 1411 { 1412 struct clocksource *cs; 1413 char name[CS_NAME_LEN]; 1414 ssize_t ret; 1415 1416 ret = sysfs_get_uname(buf, name, count); 1417 if (ret < 0) 1418 return ret; 1419 1420 ret = -ENODEV; 1421 mutex_lock(&clocksource_mutex); 1422 list_for_each_entry(cs, &clocksource_list, list) { 1423 if (strcmp(cs->name, name)) 1424 continue; 1425 ret = clocksource_unbind(cs); 1426 break; 1427 } 1428 mutex_unlock(&clocksource_mutex); 1429 1430 return ret ? ret : count; 1431 } 1432 static DEVICE_ATTR_WO(unbind_clocksource); 1433 1434 /** 1435 * available_clocksource_show - sysfs interface for listing clocksource 1436 * @dev: unused 1437 * @attr: unused 1438 * @buf: char buffer to be filled with clocksource list 1439 * 1440 * Provides sysfs interface for listing registered clocksources 1441 */ 1442 static ssize_t available_clocksource_show(struct device *dev, 1443 struct device_attribute *attr, 1444 char *buf) 1445 { 1446 struct clocksource *src; 1447 ssize_t count = 0; 1448 1449 mutex_lock(&clocksource_mutex); 1450 list_for_each_entry(src, &clocksource_list, list) { 1451 /* 1452 * Don't show non-HRES clocksource if the tick code is 1453 * in one shot mode (highres=on or nohz=on) 1454 */ 1455 if (!tick_oneshot_mode_active() || 1456 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 1457 count += snprintf(buf + count, 1458 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), 1459 "%s ", src->name); 1460 } 1461 mutex_unlock(&clocksource_mutex); 1462 1463 count += snprintf(buf + count, 1464 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n"); 1465 1466 return count; 1467 } 1468 static DEVICE_ATTR_RO(available_clocksource); 1469 1470 static struct attribute *clocksource_attrs[] = { 1471 &dev_attr_current_clocksource.attr, 1472 &dev_attr_unbind_clocksource.attr, 1473 &dev_attr_available_clocksource.attr, 1474 NULL 1475 }; 1476 ATTRIBUTE_GROUPS(clocksource); 1477 1478 static const struct bus_type clocksource_subsys = { 1479 .name = "clocksource", 1480 .dev_name = "clocksource", 1481 }; 1482 1483 static struct device device_clocksource = { 1484 .id = 0, 1485 .bus = &clocksource_subsys, 1486 .groups = clocksource_groups, 1487 }; 1488 1489 static int __init init_clocksource_sysfs(void) 1490 { 1491 int error = subsys_system_register(&clocksource_subsys, NULL); 1492 1493 if (!error) 1494 error = device_register(&device_clocksource); 1495 1496 return error; 1497 } 1498 1499 device_initcall(init_clocksource_sysfs); 1500 #endif /* CONFIG_SYSFS */ 1501 1502 /** 1503 * boot_override_clocksource - boot clock override 1504 * @str: override name 1505 * 1506 * Takes a clocksource= boot argument and uses it 1507 * as the clocksource override name. 1508 */ 1509 static int __init boot_override_clocksource(char* str) 1510 { 1511 mutex_lock(&clocksource_mutex); 1512 if (str) 1513 strscpy(override_name, str); 1514 mutex_unlock(&clocksource_mutex); 1515 return 1; 1516 } 1517 1518 __setup("clocksource=", boot_override_clocksource); 1519 1520 /** 1521 * boot_override_clock - Compatibility layer for deprecated boot option 1522 * @str: override name 1523 * 1524 * DEPRECATED! Takes a clock= boot argument and uses it 1525 * as the clocksource override name 1526 */ 1527 static int __init boot_override_clock(char* str) 1528 { 1529 if (!strcmp(str, "pmtmr")) { 1530 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n"); 1531 return boot_override_clocksource("acpi_pm"); 1532 } 1533 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n"); 1534 return boot_override_clocksource(str); 1535 } 1536 1537 __setup("clock=", boot_override_clock); 1538