1 // SPDX-License-Identifier: GPL-2.0+ 2 /* 3 * This file contains the functions which manage clocksource drivers. 4 * 5 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com) 6 */ 7 8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 9 10 #include <linux/device.h> 11 #include <linux/clocksource.h> 12 #include <linux/init.h> 13 #include <linux/module.h> 14 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */ 15 #include <linux/tick.h> 16 #include <linux/kthread.h> 17 #include <linux/prandom.h> 18 #include <linux/cpu.h> 19 20 #include "tick-internal.h" 21 #include "timekeeping_internal.h" 22 23 /** 24 * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks 25 * @mult: pointer to mult variable 26 * @shift: pointer to shift variable 27 * @from: frequency to convert from 28 * @to: frequency to convert to 29 * @maxsec: guaranteed runtime conversion range in seconds 30 * 31 * The function evaluates the shift/mult pair for the scaled math 32 * operations of clocksources and clockevents. 33 * 34 * @to and @from are frequency values in HZ. For clock sources @to is 35 * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock 36 * event @to is the counter frequency and @from is NSEC_PER_SEC. 37 * 38 * The @maxsec conversion range argument controls the time frame in 39 * seconds which must be covered by the runtime conversion with the 40 * calculated mult and shift factors. This guarantees that no 64bit 41 * overflow happens when the input value of the conversion is 42 * multiplied with the calculated mult factor. Larger ranges may 43 * reduce the conversion accuracy by choosing smaller mult and shift 44 * factors. 45 */ 46 void 47 clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec) 48 { 49 u64 tmp; 50 u32 sft, sftacc= 32; 51 52 /* 53 * Calculate the shift factor which is limiting the conversion 54 * range: 55 */ 56 tmp = ((u64)maxsec * from) >> 32; 57 while (tmp) { 58 tmp >>=1; 59 sftacc--; 60 } 61 62 /* 63 * Find the conversion shift/mult pair which has the best 64 * accuracy and fits the maxsec conversion range: 65 */ 66 for (sft = 32; sft > 0; sft--) { 67 tmp = (u64) to << sft; 68 tmp += from / 2; 69 do_div(tmp, from); 70 if ((tmp >> sftacc) == 0) 71 break; 72 } 73 *mult = tmp; 74 *shift = sft; 75 } 76 EXPORT_SYMBOL_GPL(clocks_calc_mult_shift); 77 78 /*[Clocksource internal variables]--------- 79 * curr_clocksource: 80 * currently selected clocksource. 81 * suspend_clocksource: 82 * used to calculate the suspend time. 83 * clocksource_list: 84 * linked list with the registered clocksources 85 * clocksource_mutex: 86 * protects manipulations to curr_clocksource and the clocksource_list 87 * override_name: 88 * Name of the user-specified clocksource. 89 */ 90 static struct clocksource *curr_clocksource; 91 static struct clocksource *suspend_clocksource; 92 static LIST_HEAD(clocksource_list); 93 static DEFINE_MUTEX(clocksource_mutex); 94 static char override_name[CS_NAME_LEN]; 95 static int finished_booting; 96 static u64 suspend_start; 97 98 /* 99 * Interval: 0.5sec. 100 */ 101 #define WATCHDOG_INTERVAL (HZ >> 1) 102 103 /* 104 * Threshold: 0.0312s, when doubled: 0.0625s. 105 * Also a default for cs->uncertainty_margin when registering clocks. 106 */ 107 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5) 108 109 /* 110 * Maximum permissible delay between two readouts of the watchdog 111 * clocksource surrounding a read of the clocksource being validated. 112 * This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as 113 * a lower bound for cs->uncertainty_margin values when registering clocks. 114 * 115 * The default of 500 parts per million is based on NTP's limits. 116 * If a clocksource is good enough for NTP, it is good enough for us! 117 */ 118 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 119 #define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US 120 #else 121 #define MAX_SKEW_USEC (125 * WATCHDOG_INTERVAL / HZ) 122 #endif 123 124 #define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC) 125 126 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG 127 static void clocksource_watchdog_work(struct work_struct *work); 128 static void clocksource_select(void); 129 130 static LIST_HEAD(watchdog_list); 131 static struct clocksource *watchdog; 132 static struct timer_list watchdog_timer; 133 static DECLARE_WORK(watchdog_work, clocksource_watchdog_work); 134 static DEFINE_SPINLOCK(watchdog_lock); 135 static int watchdog_running; 136 static atomic_t watchdog_reset_pending; 137 138 static inline void clocksource_watchdog_lock(unsigned long *flags) 139 { 140 spin_lock_irqsave(&watchdog_lock, *flags); 141 } 142 143 static inline void clocksource_watchdog_unlock(unsigned long *flags) 144 { 145 spin_unlock_irqrestore(&watchdog_lock, *flags); 146 } 147 148 static int clocksource_watchdog_kthread(void *data); 149 static void __clocksource_change_rating(struct clocksource *cs, int rating); 150 151 static void clocksource_watchdog_work(struct work_struct *work) 152 { 153 /* 154 * We cannot directly run clocksource_watchdog_kthread() here, because 155 * clocksource_select() calls timekeeping_notify() which uses 156 * stop_machine(). One cannot use stop_machine() from a workqueue() due 157 * lock inversions wrt CPU hotplug. 158 * 159 * Also, we only ever run this work once or twice during the lifetime 160 * of the kernel, so there is no point in creating a more permanent 161 * kthread for this. 162 * 163 * If kthread_run fails the next watchdog scan over the 164 * watchdog_list will find the unstable clock again. 165 */ 166 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog"); 167 } 168 169 static void __clocksource_unstable(struct clocksource *cs) 170 { 171 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG); 172 cs->flags |= CLOCK_SOURCE_UNSTABLE; 173 174 /* 175 * If the clocksource is registered clocksource_watchdog_kthread() will 176 * re-rate and re-select. 177 */ 178 if (list_empty(&cs->list)) { 179 cs->rating = 0; 180 return; 181 } 182 183 if (cs->mark_unstable) 184 cs->mark_unstable(cs); 185 186 /* kick clocksource_watchdog_kthread() */ 187 if (finished_booting) 188 schedule_work(&watchdog_work); 189 } 190 191 /** 192 * clocksource_mark_unstable - mark clocksource unstable via watchdog 193 * @cs: clocksource to be marked unstable 194 * 195 * This function is called by the x86 TSC code to mark clocksources as unstable; 196 * it defers demotion and re-selection to a kthread. 197 */ 198 void clocksource_mark_unstable(struct clocksource *cs) 199 { 200 unsigned long flags; 201 202 spin_lock_irqsave(&watchdog_lock, flags); 203 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) { 204 if (!list_empty(&cs->list) && list_empty(&cs->wd_list)) 205 list_add(&cs->wd_list, &watchdog_list); 206 __clocksource_unstable(cs); 207 } 208 spin_unlock_irqrestore(&watchdog_lock, flags); 209 } 210 211 ulong max_cswd_read_retries = 2; 212 module_param(max_cswd_read_retries, ulong, 0644); 213 EXPORT_SYMBOL_GPL(max_cswd_read_retries); 214 static int verify_n_cpus = 8; 215 module_param(verify_n_cpus, int, 0644); 216 217 enum wd_read_status { 218 WD_READ_SUCCESS, 219 WD_READ_UNSTABLE, 220 WD_READ_SKIP 221 }; 222 223 static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow) 224 { 225 unsigned int nretries; 226 u64 wd_end, wd_end2, wd_delta; 227 int64_t wd_delay, wd_seq_delay; 228 229 for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) { 230 local_irq_disable(); 231 *wdnow = watchdog->read(watchdog); 232 *csnow = cs->read(cs); 233 wd_end = watchdog->read(watchdog); 234 wd_end2 = watchdog->read(watchdog); 235 local_irq_enable(); 236 237 wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask); 238 wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, 239 watchdog->shift); 240 if (wd_delay <= WATCHDOG_MAX_SKEW) { 241 if (nretries > 1 || nretries >= max_cswd_read_retries) { 242 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n", 243 smp_processor_id(), watchdog->name, nretries); 244 } 245 return WD_READ_SUCCESS; 246 } 247 248 /* 249 * Now compute delay in consecutive watchdog read to see if 250 * there is too much external interferences that cause 251 * significant delay in reading both clocksource and watchdog. 252 * 253 * If consecutive WD read-back delay > WATCHDOG_MAX_SKEW/2, 254 * report system busy, reinit the watchdog and skip the current 255 * watchdog test. 256 */ 257 wd_delta = clocksource_delta(wd_end2, wd_end, watchdog->mask); 258 wd_seq_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, watchdog->shift); 259 if (wd_seq_delay > WATCHDOG_MAX_SKEW/2) 260 goto skip_test; 261 } 262 263 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", 264 smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name); 265 return WD_READ_UNSTABLE; 266 267 skip_test: 268 pr_info("timekeeping watchdog on CPU%d: %s wd-wd read-back delay of %lldns\n", 269 smp_processor_id(), watchdog->name, wd_seq_delay); 270 pr_info("wd-%s-wd read-back delay of %lldns, clock-skew test skipped!\n", 271 cs->name, wd_delay); 272 return WD_READ_SKIP; 273 } 274 275 static u64 csnow_mid; 276 static cpumask_t cpus_ahead; 277 static cpumask_t cpus_behind; 278 static cpumask_t cpus_chosen; 279 280 static void clocksource_verify_choose_cpus(void) 281 { 282 int cpu, i, n = verify_n_cpus; 283 284 if (n < 0) { 285 /* Check all of the CPUs. */ 286 cpumask_copy(&cpus_chosen, cpu_online_mask); 287 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); 288 return; 289 } 290 291 /* If no checking desired, or no other CPU to check, leave. */ 292 cpumask_clear(&cpus_chosen); 293 if (n == 0 || num_online_cpus() <= 1) 294 return; 295 296 /* Make sure to select at least one CPU other than the current CPU. */ 297 cpu = cpumask_first(cpu_online_mask); 298 if (cpu == smp_processor_id()) 299 cpu = cpumask_next(cpu, cpu_online_mask); 300 if (WARN_ON_ONCE(cpu >= nr_cpu_ids)) 301 return; 302 cpumask_set_cpu(cpu, &cpus_chosen); 303 304 /* Force a sane value for the boot parameter. */ 305 if (n > nr_cpu_ids) 306 n = nr_cpu_ids; 307 308 /* 309 * Randomly select the specified number of CPUs. If the same 310 * CPU is selected multiple times, that CPU is checked only once, 311 * and no replacement CPU is selected. This gracefully handles 312 * situations where verify_n_cpus is greater than the number of 313 * CPUs that are currently online. 314 */ 315 for (i = 1; i < n; i++) { 316 cpu = get_random_u32_below(nr_cpu_ids); 317 cpu = cpumask_next(cpu - 1, cpu_online_mask); 318 if (cpu >= nr_cpu_ids) 319 cpu = cpumask_first(cpu_online_mask); 320 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids)) 321 cpumask_set_cpu(cpu, &cpus_chosen); 322 } 323 324 /* Don't verify ourselves. */ 325 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); 326 } 327 328 static void clocksource_verify_one_cpu(void *csin) 329 { 330 struct clocksource *cs = (struct clocksource *)csin; 331 332 csnow_mid = cs->read(cs); 333 } 334 335 void clocksource_verify_percpu(struct clocksource *cs) 336 { 337 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX; 338 u64 csnow_begin, csnow_end; 339 int cpu, testcpu; 340 s64 delta; 341 342 if (verify_n_cpus == 0) 343 return; 344 cpumask_clear(&cpus_ahead); 345 cpumask_clear(&cpus_behind); 346 cpus_read_lock(); 347 preempt_disable(); 348 clocksource_verify_choose_cpus(); 349 if (cpumask_empty(&cpus_chosen)) { 350 preempt_enable(); 351 cpus_read_unlock(); 352 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name); 353 return; 354 } 355 testcpu = smp_processor_id(); 356 pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen)); 357 for_each_cpu(cpu, &cpus_chosen) { 358 if (cpu == testcpu) 359 continue; 360 csnow_begin = cs->read(cs); 361 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1); 362 csnow_end = cs->read(cs); 363 delta = (s64)((csnow_mid - csnow_begin) & cs->mask); 364 if (delta < 0) 365 cpumask_set_cpu(cpu, &cpus_behind); 366 delta = (csnow_end - csnow_mid) & cs->mask; 367 if (delta < 0) 368 cpumask_set_cpu(cpu, &cpus_ahead); 369 delta = clocksource_delta(csnow_end, csnow_begin, cs->mask); 370 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift); 371 if (cs_nsec > cs_nsec_max) 372 cs_nsec_max = cs_nsec; 373 if (cs_nsec < cs_nsec_min) 374 cs_nsec_min = cs_nsec; 375 } 376 preempt_enable(); 377 cpus_read_unlock(); 378 if (!cpumask_empty(&cpus_ahead)) 379 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n", 380 cpumask_pr_args(&cpus_ahead), testcpu, cs->name); 381 if (!cpumask_empty(&cpus_behind)) 382 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n", 383 cpumask_pr_args(&cpus_behind), testcpu, cs->name); 384 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind)) 385 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n", 386 testcpu, cs_nsec_min, cs_nsec_max, cs->name); 387 } 388 EXPORT_SYMBOL_GPL(clocksource_verify_percpu); 389 390 static inline void clocksource_reset_watchdog(void) 391 { 392 struct clocksource *cs; 393 394 list_for_each_entry(cs, &watchdog_list, wd_list) 395 cs->flags &= ~CLOCK_SOURCE_WATCHDOG; 396 } 397 398 399 static void clocksource_watchdog(struct timer_list *unused) 400 { 401 u64 csnow, wdnow, cslast, wdlast, delta; 402 int next_cpu, reset_pending; 403 int64_t wd_nsec, cs_nsec; 404 struct clocksource *cs; 405 enum wd_read_status read_ret; 406 unsigned long extra_wait = 0; 407 u32 md; 408 409 spin_lock(&watchdog_lock); 410 if (!watchdog_running) 411 goto out; 412 413 reset_pending = atomic_read(&watchdog_reset_pending); 414 415 list_for_each_entry(cs, &watchdog_list, wd_list) { 416 417 /* Clocksource already marked unstable? */ 418 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 419 if (finished_booting) 420 schedule_work(&watchdog_work); 421 continue; 422 } 423 424 read_ret = cs_watchdog_read(cs, &csnow, &wdnow); 425 426 if (read_ret == WD_READ_UNSTABLE) { 427 /* Clock readout unreliable, so give it up. */ 428 __clocksource_unstable(cs); 429 continue; 430 } 431 432 /* 433 * When WD_READ_SKIP is returned, it means the system is likely 434 * under very heavy load, where the latency of reading 435 * watchdog/clocksource is very big, and affect the accuracy of 436 * watchdog check. So give system some space and suspend the 437 * watchdog check for 5 minutes. 438 */ 439 if (read_ret == WD_READ_SKIP) { 440 /* 441 * As the watchdog timer will be suspended, and 442 * cs->last could keep unchanged for 5 minutes, reset 443 * the counters. 444 */ 445 clocksource_reset_watchdog(); 446 extra_wait = HZ * 300; 447 break; 448 } 449 450 /* Clocksource initialized ? */ 451 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) || 452 atomic_read(&watchdog_reset_pending)) { 453 cs->flags |= CLOCK_SOURCE_WATCHDOG; 454 cs->wd_last = wdnow; 455 cs->cs_last = csnow; 456 continue; 457 } 458 459 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask); 460 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult, 461 watchdog->shift); 462 463 delta = clocksource_delta(csnow, cs->cs_last, cs->mask); 464 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift); 465 wdlast = cs->wd_last; /* save these in case we print them */ 466 cslast = cs->cs_last; 467 cs->cs_last = csnow; 468 cs->wd_last = wdnow; 469 470 if (atomic_read(&watchdog_reset_pending)) 471 continue; 472 473 /* Check the deviation from the watchdog clocksource. */ 474 md = cs->uncertainty_margin + watchdog->uncertainty_margin; 475 if (abs(cs_nsec - wd_nsec) > md) { 476 u64 cs_wd_msec; 477 u64 wd_msec; 478 u32 wd_rem; 479 480 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n", 481 smp_processor_id(), cs->name); 482 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n", 483 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask); 484 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n", 485 cs->name, cs_nsec, csnow, cslast, cs->mask); 486 cs_wd_msec = div_u64_rem(cs_nsec - wd_nsec, 1000U * 1000U, &wd_rem); 487 wd_msec = div_u64_rem(wd_nsec, 1000U * 1000U, &wd_rem); 488 pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n", 489 cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec); 490 if (curr_clocksource == cs) 491 pr_warn(" '%s' is current clocksource.\n", cs->name); 492 else if (curr_clocksource) 493 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name); 494 else 495 pr_warn(" No current clocksource.\n"); 496 __clocksource_unstable(cs); 497 continue; 498 } 499 500 if (cs == curr_clocksource && cs->tick_stable) 501 cs->tick_stable(cs); 502 503 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && 504 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) && 505 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) { 506 /* Mark it valid for high-res. */ 507 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 508 509 /* 510 * clocksource_done_booting() will sort it if 511 * finished_booting is not set yet. 512 */ 513 if (!finished_booting) 514 continue; 515 516 /* 517 * If this is not the current clocksource let 518 * the watchdog thread reselect it. Due to the 519 * change to high res this clocksource might 520 * be preferred now. If it is the current 521 * clocksource let the tick code know about 522 * that change. 523 */ 524 if (cs != curr_clocksource) { 525 cs->flags |= CLOCK_SOURCE_RESELECT; 526 schedule_work(&watchdog_work); 527 } else { 528 tick_clock_notify(); 529 } 530 } 531 } 532 533 /* 534 * We only clear the watchdog_reset_pending, when we did a 535 * full cycle through all clocksources. 536 */ 537 if (reset_pending) 538 atomic_dec(&watchdog_reset_pending); 539 540 /* 541 * Cycle through CPUs to check if the CPUs stay synchronized 542 * to each other. 543 */ 544 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask); 545 if (next_cpu >= nr_cpu_ids) 546 next_cpu = cpumask_first(cpu_online_mask); 547 548 /* 549 * Arm timer if not already pending: could race with concurrent 550 * pair clocksource_stop_watchdog() clocksource_start_watchdog(). 551 */ 552 if (!timer_pending(&watchdog_timer)) { 553 watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait; 554 add_timer_on(&watchdog_timer, next_cpu); 555 } 556 out: 557 spin_unlock(&watchdog_lock); 558 } 559 560 static inline void clocksource_start_watchdog(void) 561 { 562 if (watchdog_running || !watchdog || list_empty(&watchdog_list)) 563 return; 564 timer_setup(&watchdog_timer, clocksource_watchdog, 0); 565 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL; 566 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask)); 567 watchdog_running = 1; 568 } 569 570 static inline void clocksource_stop_watchdog(void) 571 { 572 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list))) 573 return; 574 del_timer(&watchdog_timer); 575 watchdog_running = 0; 576 } 577 578 static void clocksource_resume_watchdog(void) 579 { 580 atomic_inc(&watchdog_reset_pending); 581 } 582 583 static void clocksource_enqueue_watchdog(struct clocksource *cs) 584 { 585 INIT_LIST_HEAD(&cs->wd_list); 586 587 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { 588 /* cs is a clocksource to be watched. */ 589 list_add(&cs->wd_list, &watchdog_list); 590 cs->flags &= ~CLOCK_SOURCE_WATCHDOG; 591 } else { 592 /* cs is a watchdog. */ 593 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 594 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 595 } 596 } 597 598 static void clocksource_select_watchdog(bool fallback) 599 { 600 struct clocksource *cs, *old_wd; 601 unsigned long flags; 602 603 spin_lock_irqsave(&watchdog_lock, flags); 604 /* save current watchdog */ 605 old_wd = watchdog; 606 if (fallback) 607 watchdog = NULL; 608 609 list_for_each_entry(cs, &clocksource_list, list) { 610 /* cs is a clocksource to be watched. */ 611 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) 612 continue; 613 614 /* Skip current if we were requested for a fallback. */ 615 if (fallback && cs == old_wd) 616 continue; 617 618 /* Pick the best watchdog. */ 619 if (!watchdog || cs->rating > watchdog->rating) 620 watchdog = cs; 621 } 622 /* If we failed to find a fallback restore the old one. */ 623 if (!watchdog) 624 watchdog = old_wd; 625 626 /* If we changed the watchdog we need to reset cycles. */ 627 if (watchdog != old_wd) 628 clocksource_reset_watchdog(); 629 630 /* Check if the watchdog timer needs to be started. */ 631 clocksource_start_watchdog(); 632 spin_unlock_irqrestore(&watchdog_lock, flags); 633 } 634 635 static void clocksource_dequeue_watchdog(struct clocksource *cs) 636 { 637 if (cs != watchdog) { 638 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { 639 /* cs is a watched clocksource. */ 640 list_del_init(&cs->wd_list); 641 /* Check if the watchdog timer needs to be stopped. */ 642 clocksource_stop_watchdog(); 643 } 644 } 645 } 646 647 static int __clocksource_watchdog_kthread(void) 648 { 649 struct clocksource *cs, *tmp; 650 unsigned long flags; 651 int select = 0; 652 653 /* Do any required per-CPU skew verification. */ 654 if (curr_clocksource && 655 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE && 656 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU) 657 clocksource_verify_percpu(curr_clocksource); 658 659 spin_lock_irqsave(&watchdog_lock, flags); 660 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) { 661 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 662 list_del_init(&cs->wd_list); 663 __clocksource_change_rating(cs, 0); 664 select = 1; 665 } 666 if (cs->flags & CLOCK_SOURCE_RESELECT) { 667 cs->flags &= ~CLOCK_SOURCE_RESELECT; 668 select = 1; 669 } 670 } 671 /* Check if the watchdog timer needs to be stopped. */ 672 clocksource_stop_watchdog(); 673 spin_unlock_irqrestore(&watchdog_lock, flags); 674 675 return select; 676 } 677 678 static int clocksource_watchdog_kthread(void *data) 679 { 680 mutex_lock(&clocksource_mutex); 681 if (__clocksource_watchdog_kthread()) 682 clocksource_select(); 683 mutex_unlock(&clocksource_mutex); 684 return 0; 685 } 686 687 static bool clocksource_is_watchdog(struct clocksource *cs) 688 { 689 return cs == watchdog; 690 } 691 692 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */ 693 694 static void clocksource_enqueue_watchdog(struct clocksource *cs) 695 { 696 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 697 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 698 } 699 700 static void clocksource_select_watchdog(bool fallback) { } 701 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { } 702 static inline void clocksource_resume_watchdog(void) { } 703 static inline int __clocksource_watchdog_kthread(void) { return 0; } 704 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; } 705 void clocksource_mark_unstable(struct clocksource *cs) { } 706 707 static inline void clocksource_watchdog_lock(unsigned long *flags) { } 708 static inline void clocksource_watchdog_unlock(unsigned long *flags) { } 709 710 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */ 711 712 static bool clocksource_is_suspend(struct clocksource *cs) 713 { 714 return cs == suspend_clocksource; 715 } 716 717 static void __clocksource_suspend_select(struct clocksource *cs) 718 { 719 /* 720 * Skip the clocksource which will be stopped in suspend state. 721 */ 722 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP)) 723 return; 724 725 /* 726 * The nonstop clocksource can be selected as the suspend clocksource to 727 * calculate the suspend time, so it should not supply suspend/resume 728 * interfaces to suspend the nonstop clocksource when system suspends. 729 */ 730 if (cs->suspend || cs->resume) { 731 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n", 732 cs->name); 733 } 734 735 /* Pick the best rating. */ 736 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating) 737 suspend_clocksource = cs; 738 } 739 740 /** 741 * clocksource_suspend_select - Select the best clocksource for suspend timing 742 * @fallback: if select a fallback clocksource 743 */ 744 static void clocksource_suspend_select(bool fallback) 745 { 746 struct clocksource *cs, *old_suspend; 747 748 old_suspend = suspend_clocksource; 749 if (fallback) 750 suspend_clocksource = NULL; 751 752 list_for_each_entry(cs, &clocksource_list, list) { 753 /* Skip current if we were requested for a fallback. */ 754 if (fallback && cs == old_suspend) 755 continue; 756 757 __clocksource_suspend_select(cs); 758 } 759 } 760 761 /** 762 * clocksource_start_suspend_timing - Start measuring the suspend timing 763 * @cs: current clocksource from timekeeping 764 * @start_cycles: current cycles from timekeeping 765 * 766 * This function will save the start cycle values of suspend timer to calculate 767 * the suspend time when resuming system. 768 * 769 * This function is called late in the suspend process from timekeeping_suspend(), 770 * that means processes are frozen, non-boot cpus and interrupts are disabled 771 * now. It is therefore possible to start the suspend timer without taking the 772 * clocksource mutex. 773 */ 774 void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles) 775 { 776 if (!suspend_clocksource) 777 return; 778 779 /* 780 * If current clocksource is the suspend timer, we should use the 781 * tkr_mono.cycle_last value as suspend_start to avoid same reading 782 * from suspend timer. 783 */ 784 if (clocksource_is_suspend(cs)) { 785 suspend_start = start_cycles; 786 return; 787 } 788 789 if (suspend_clocksource->enable && 790 suspend_clocksource->enable(suspend_clocksource)) { 791 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n"); 792 return; 793 } 794 795 suspend_start = suspend_clocksource->read(suspend_clocksource); 796 } 797 798 /** 799 * clocksource_stop_suspend_timing - Stop measuring the suspend timing 800 * @cs: current clocksource from timekeeping 801 * @cycle_now: current cycles from timekeeping 802 * 803 * This function will calculate the suspend time from suspend timer. 804 * 805 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource. 806 * 807 * This function is called early in the resume process from timekeeping_resume(), 808 * that means there is only one cpu, no processes are running and the interrupts 809 * are disabled. It is therefore possible to stop the suspend timer without 810 * taking the clocksource mutex. 811 */ 812 u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now) 813 { 814 u64 now, delta, nsec = 0; 815 816 if (!suspend_clocksource) 817 return 0; 818 819 /* 820 * If current clocksource is the suspend timer, we should use the 821 * tkr_mono.cycle_last value from timekeeping as current cycle to 822 * avoid same reading from suspend timer. 823 */ 824 if (clocksource_is_suspend(cs)) 825 now = cycle_now; 826 else 827 now = suspend_clocksource->read(suspend_clocksource); 828 829 if (now > suspend_start) { 830 delta = clocksource_delta(now, suspend_start, 831 suspend_clocksource->mask); 832 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult, 833 suspend_clocksource->shift); 834 } 835 836 /* 837 * Disable the suspend timer to save power if current clocksource is 838 * not the suspend timer. 839 */ 840 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable) 841 suspend_clocksource->disable(suspend_clocksource); 842 843 return nsec; 844 } 845 846 /** 847 * clocksource_suspend - suspend the clocksource(s) 848 */ 849 void clocksource_suspend(void) 850 { 851 struct clocksource *cs; 852 853 list_for_each_entry_reverse(cs, &clocksource_list, list) 854 if (cs->suspend) 855 cs->suspend(cs); 856 } 857 858 /** 859 * clocksource_resume - resume the clocksource(s) 860 */ 861 void clocksource_resume(void) 862 { 863 struct clocksource *cs; 864 865 list_for_each_entry(cs, &clocksource_list, list) 866 if (cs->resume) 867 cs->resume(cs); 868 869 clocksource_resume_watchdog(); 870 } 871 872 /** 873 * clocksource_touch_watchdog - Update watchdog 874 * 875 * Update the watchdog after exception contexts such as kgdb so as not 876 * to incorrectly trip the watchdog. This might fail when the kernel 877 * was stopped in code which holds watchdog_lock. 878 */ 879 void clocksource_touch_watchdog(void) 880 { 881 clocksource_resume_watchdog(); 882 } 883 884 /** 885 * clocksource_max_adjustment- Returns max adjustment amount 886 * @cs: Pointer to clocksource 887 * 888 */ 889 static u32 clocksource_max_adjustment(struct clocksource *cs) 890 { 891 u64 ret; 892 /* 893 * We won't try to correct for more than 11% adjustments (110,000 ppm), 894 */ 895 ret = (u64)cs->mult * 11; 896 do_div(ret,100); 897 return (u32)ret; 898 } 899 900 /** 901 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted 902 * @mult: cycle to nanosecond multiplier 903 * @shift: cycle to nanosecond divisor (power of two) 904 * @maxadj: maximum adjustment value to mult (~11%) 905 * @mask: bitmask for two's complement subtraction of non 64 bit counters 906 * @max_cyc: maximum cycle value before potential overflow (does not include 907 * any safety margin) 908 * 909 * NOTE: This function includes a safety margin of 50%, in other words, we 910 * return half the number of nanoseconds the hardware counter can technically 911 * cover. This is done so that we can potentially detect problems caused by 912 * delayed timers or bad hardware, which might result in time intervals that 913 * are larger than what the math used can handle without overflows. 914 */ 915 u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc) 916 { 917 u64 max_nsecs, max_cycles; 918 919 /* 920 * Calculate the maximum number of cycles that we can pass to the 921 * cyc2ns() function without overflowing a 64-bit result. 922 */ 923 max_cycles = ULLONG_MAX; 924 do_div(max_cycles, mult+maxadj); 925 926 /* 927 * The actual maximum number of cycles we can defer the clocksource is 928 * determined by the minimum of max_cycles and mask. 929 * Note: Here we subtract the maxadj to make sure we don't sleep for 930 * too long if there's a large negative adjustment. 931 */ 932 max_cycles = min(max_cycles, mask); 933 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift); 934 935 /* return the max_cycles value as well if requested */ 936 if (max_cyc) 937 *max_cyc = max_cycles; 938 939 /* Return 50% of the actual maximum, so we can detect bad values */ 940 max_nsecs >>= 1; 941 942 return max_nsecs; 943 } 944 945 /** 946 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles 947 * @cs: Pointer to clocksource to be updated 948 * 949 */ 950 static inline void clocksource_update_max_deferment(struct clocksource *cs) 951 { 952 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift, 953 cs->maxadj, cs->mask, 954 &cs->max_cycles); 955 } 956 957 static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur) 958 { 959 struct clocksource *cs; 960 961 if (!finished_booting || list_empty(&clocksource_list)) 962 return NULL; 963 964 /* 965 * We pick the clocksource with the highest rating. If oneshot 966 * mode is active, we pick the highres valid clocksource with 967 * the best rating. 968 */ 969 list_for_each_entry(cs, &clocksource_list, list) { 970 if (skipcur && cs == curr_clocksource) 971 continue; 972 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 973 continue; 974 return cs; 975 } 976 return NULL; 977 } 978 979 static void __clocksource_select(bool skipcur) 980 { 981 bool oneshot = tick_oneshot_mode_active(); 982 struct clocksource *best, *cs; 983 984 /* Find the best suitable clocksource */ 985 best = clocksource_find_best(oneshot, skipcur); 986 if (!best) 987 return; 988 989 if (!strlen(override_name)) 990 goto found; 991 992 /* Check for the override clocksource. */ 993 list_for_each_entry(cs, &clocksource_list, list) { 994 if (skipcur && cs == curr_clocksource) 995 continue; 996 if (strcmp(cs->name, override_name) != 0) 997 continue; 998 /* 999 * Check to make sure we don't switch to a non-highres 1000 * capable clocksource if the tick code is in oneshot 1001 * mode (highres or nohz) 1002 */ 1003 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) { 1004 /* Override clocksource cannot be used. */ 1005 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 1006 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n", 1007 cs->name); 1008 override_name[0] = 0; 1009 } else { 1010 /* 1011 * The override cannot be currently verified. 1012 * Deferring to let the watchdog check. 1013 */ 1014 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n", 1015 cs->name); 1016 } 1017 } else 1018 /* Override clocksource can be used. */ 1019 best = cs; 1020 break; 1021 } 1022 1023 found: 1024 if (curr_clocksource != best && !timekeeping_notify(best)) { 1025 pr_info("Switched to clocksource %s\n", best->name); 1026 curr_clocksource = best; 1027 } 1028 } 1029 1030 /** 1031 * clocksource_select - Select the best clocksource available 1032 * 1033 * Private function. Must hold clocksource_mutex when called. 1034 * 1035 * Select the clocksource with the best rating, or the clocksource, 1036 * which is selected by userspace override. 1037 */ 1038 static void clocksource_select(void) 1039 { 1040 __clocksource_select(false); 1041 } 1042 1043 static void clocksource_select_fallback(void) 1044 { 1045 __clocksource_select(true); 1046 } 1047 1048 /* 1049 * clocksource_done_booting - Called near the end of core bootup 1050 * 1051 * Hack to avoid lots of clocksource churn at boot time. 1052 * We use fs_initcall because we want this to start before 1053 * device_initcall but after subsys_initcall. 1054 */ 1055 static int __init clocksource_done_booting(void) 1056 { 1057 mutex_lock(&clocksource_mutex); 1058 curr_clocksource = clocksource_default_clock(); 1059 finished_booting = 1; 1060 /* 1061 * Run the watchdog first to eliminate unstable clock sources 1062 */ 1063 __clocksource_watchdog_kthread(); 1064 clocksource_select(); 1065 mutex_unlock(&clocksource_mutex); 1066 return 0; 1067 } 1068 fs_initcall(clocksource_done_booting); 1069 1070 /* 1071 * Enqueue the clocksource sorted by rating 1072 */ 1073 static void clocksource_enqueue(struct clocksource *cs) 1074 { 1075 struct list_head *entry = &clocksource_list; 1076 struct clocksource *tmp; 1077 1078 list_for_each_entry(tmp, &clocksource_list, list) { 1079 /* Keep track of the place, where to insert */ 1080 if (tmp->rating < cs->rating) 1081 break; 1082 entry = &tmp->list; 1083 } 1084 list_add(&cs->list, entry); 1085 } 1086 1087 /** 1088 * __clocksource_update_freq_scale - Used update clocksource with new freq 1089 * @cs: clocksource to be registered 1090 * @scale: Scale factor multiplied against freq to get clocksource hz 1091 * @freq: clocksource frequency (cycles per second) divided by scale 1092 * 1093 * This should only be called from the clocksource->enable() method. 1094 * 1095 * This *SHOULD NOT* be called directly! Please use the 1096 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper 1097 * functions. 1098 */ 1099 void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq) 1100 { 1101 u64 sec; 1102 1103 /* 1104 * Default clocksources are *special* and self-define their mult/shift. 1105 * But, you're not special, so you should specify a freq value. 1106 */ 1107 if (freq) { 1108 /* 1109 * Calc the maximum number of seconds which we can run before 1110 * wrapping around. For clocksources which have a mask > 32-bit 1111 * we need to limit the max sleep time to have a good 1112 * conversion precision. 10 minutes is still a reasonable 1113 * amount. That results in a shift value of 24 for a 1114 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to 1115 * ~ 0.06ppm granularity for NTP. 1116 */ 1117 sec = cs->mask; 1118 do_div(sec, freq); 1119 do_div(sec, scale); 1120 if (!sec) 1121 sec = 1; 1122 else if (sec > 600 && cs->mask > UINT_MAX) 1123 sec = 600; 1124 1125 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq, 1126 NSEC_PER_SEC / scale, sec * scale); 1127 } 1128 1129 /* 1130 * If the uncertainty margin is not specified, calculate it. 1131 * If both scale and freq are non-zero, calculate the clock 1132 * period, but bound below at 2*WATCHDOG_MAX_SKEW. However, 1133 * if either of scale or freq is zero, be very conservative and 1134 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the 1135 * uncertainty margin. Allow stupidly small uncertainty margins 1136 * to be specified by the caller for testing purposes, but warn 1137 * to discourage production use of this capability. 1138 */ 1139 if (scale && freq && !cs->uncertainty_margin) { 1140 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq); 1141 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW) 1142 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW; 1143 } else if (!cs->uncertainty_margin) { 1144 cs->uncertainty_margin = WATCHDOG_THRESHOLD; 1145 } 1146 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW); 1147 1148 /* 1149 * Ensure clocksources that have large 'mult' values don't overflow 1150 * when adjusted. 1151 */ 1152 cs->maxadj = clocksource_max_adjustment(cs); 1153 while (freq && ((cs->mult + cs->maxadj < cs->mult) 1154 || (cs->mult - cs->maxadj > cs->mult))) { 1155 cs->mult >>= 1; 1156 cs->shift--; 1157 cs->maxadj = clocksource_max_adjustment(cs); 1158 } 1159 1160 /* 1161 * Only warn for *special* clocksources that self-define 1162 * their mult/shift values and don't specify a freq. 1163 */ 1164 WARN_ONCE(cs->mult + cs->maxadj < cs->mult, 1165 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n", 1166 cs->name); 1167 1168 clocksource_update_max_deferment(cs); 1169 1170 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n", 1171 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns); 1172 } 1173 EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale); 1174 1175 /** 1176 * __clocksource_register_scale - Used to install new clocksources 1177 * @cs: clocksource to be registered 1178 * @scale: Scale factor multiplied against freq to get clocksource hz 1179 * @freq: clocksource frequency (cycles per second) divided by scale 1180 * 1181 * Returns -EBUSY if registration fails, zero otherwise. 1182 * 1183 * This *SHOULD NOT* be called directly! Please use the 1184 * clocksource_register_hz() or clocksource_register_khz helper functions. 1185 */ 1186 int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq) 1187 { 1188 unsigned long flags; 1189 1190 clocksource_arch_init(cs); 1191 1192 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX)) 1193 cs->id = CSID_GENERIC; 1194 if (cs->vdso_clock_mode < 0 || 1195 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) { 1196 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n", 1197 cs->name, cs->vdso_clock_mode); 1198 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE; 1199 } 1200 1201 /* Initialize mult/shift and max_idle_ns */ 1202 __clocksource_update_freq_scale(cs, scale, freq); 1203 1204 /* Add clocksource to the clocksource list */ 1205 mutex_lock(&clocksource_mutex); 1206 1207 clocksource_watchdog_lock(&flags); 1208 clocksource_enqueue(cs); 1209 clocksource_enqueue_watchdog(cs); 1210 clocksource_watchdog_unlock(&flags); 1211 1212 clocksource_select(); 1213 clocksource_select_watchdog(false); 1214 __clocksource_suspend_select(cs); 1215 mutex_unlock(&clocksource_mutex); 1216 return 0; 1217 } 1218 EXPORT_SYMBOL_GPL(__clocksource_register_scale); 1219 1220 static void __clocksource_change_rating(struct clocksource *cs, int rating) 1221 { 1222 list_del(&cs->list); 1223 cs->rating = rating; 1224 clocksource_enqueue(cs); 1225 } 1226 1227 /** 1228 * clocksource_change_rating - Change the rating of a registered clocksource 1229 * @cs: clocksource to be changed 1230 * @rating: new rating 1231 */ 1232 void clocksource_change_rating(struct clocksource *cs, int rating) 1233 { 1234 unsigned long flags; 1235 1236 mutex_lock(&clocksource_mutex); 1237 clocksource_watchdog_lock(&flags); 1238 __clocksource_change_rating(cs, rating); 1239 clocksource_watchdog_unlock(&flags); 1240 1241 clocksource_select(); 1242 clocksource_select_watchdog(false); 1243 clocksource_suspend_select(false); 1244 mutex_unlock(&clocksource_mutex); 1245 } 1246 EXPORT_SYMBOL(clocksource_change_rating); 1247 1248 /* 1249 * Unbind clocksource @cs. Called with clocksource_mutex held 1250 */ 1251 static int clocksource_unbind(struct clocksource *cs) 1252 { 1253 unsigned long flags; 1254 1255 if (clocksource_is_watchdog(cs)) { 1256 /* Select and try to install a replacement watchdog. */ 1257 clocksource_select_watchdog(true); 1258 if (clocksource_is_watchdog(cs)) 1259 return -EBUSY; 1260 } 1261 1262 if (cs == curr_clocksource) { 1263 /* Select and try to install a replacement clock source */ 1264 clocksource_select_fallback(); 1265 if (curr_clocksource == cs) 1266 return -EBUSY; 1267 } 1268 1269 if (clocksource_is_suspend(cs)) { 1270 /* 1271 * Select and try to install a replacement suspend clocksource. 1272 * If no replacement suspend clocksource, we will just let the 1273 * clocksource go and have no suspend clocksource. 1274 */ 1275 clocksource_suspend_select(true); 1276 } 1277 1278 clocksource_watchdog_lock(&flags); 1279 clocksource_dequeue_watchdog(cs); 1280 list_del_init(&cs->list); 1281 clocksource_watchdog_unlock(&flags); 1282 1283 return 0; 1284 } 1285 1286 /** 1287 * clocksource_unregister - remove a registered clocksource 1288 * @cs: clocksource to be unregistered 1289 */ 1290 int clocksource_unregister(struct clocksource *cs) 1291 { 1292 int ret = 0; 1293 1294 mutex_lock(&clocksource_mutex); 1295 if (!list_empty(&cs->list)) 1296 ret = clocksource_unbind(cs); 1297 mutex_unlock(&clocksource_mutex); 1298 return ret; 1299 } 1300 EXPORT_SYMBOL(clocksource_unregister); 1301 1302 #ifdef CONFIG_SYSFS 1303 /** 1304 * current_clocksource_show - sysfs interface for current clocksource 1305 * @dev: unused 1306 * @attr: unused 1307 * @buf: char buffer to be filled with clocksource list 1308 * 1309 * Provides sysfs interface for listing current clocksource. 1310 */ 1311 static ssize_t current_clocksource_show(struct device *dev, 1312 struct device_attribute *attr, 1313 char *buf) 1314 { 1315 ssize_t count = 0; 1316 1317 mutex_lock(&clocksource_mutex); 1318 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name); 1319 mutex_unlock(&clocksource_mutex); 1320 1321 return count; 1322 } 1323 1324 ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt) 1325 { 1326 size_t ret = cnt; 1327 1328 /* strings from sysfs write are not 0 terminated! */ 1329 if (!cnt || cnt >= CS_NAME_LEN) 1330 return -EINVAL; 1331 1332 /* strip of \n: */ 1333 if (buf[cnt-1] == '\n') 1334 cnt--; 1335 if (cnt > 0) 1336 memcpy(dst, buf, cnt); 1337 dst[cnt] = 0; 1338 return ret; 1339 } 1340 1341 /** 1342 * current_clocksource_store - interface for manually overriding clocksource 1343 * @dev: unused 1344 * @attr: unused 1345 * @buf: name of override clocksource 1346 * @count: length of buffer 1347 * 1348 * Takes input from sysfs interface for manually overriding the default 1349 * clocksource selection. 1350 */ 1351 static ssize_t current_clocksource_store(struct device *dev, 1352 struct device_attribute *attr, 1353 const char *buf, size_t count) 1354 { 1355 ssize_t ret; 1356 1357 mutex_lock(&clocksource_mutex); 1358 1359 ret = sysfs_get_uname(buf, override_name, count); 1360 if (ret >= 0) 1361 clocksource_select(); 1362 1363 mutex_unlock(&clocksource_mutex); 1364 1365 return ret; 1366 } 1367 static DEVICE_ATTR_RW(current_clocksource); 1368 1369 /** 1370 * unbind_clocksource_store - interface for manually unbinding clocksource 1371 * @dev: unused 1372 * @attr: unused 1373 * @buf: unused 1374 * @count: length of buffer 1375 * 1376 * Takes input from sysfs interface for manually unbinding a clocksource. 1377 */ 1378 static ssize_t unbind_clocksource_store(struct device *dev, 1379 struct device_attribute *attr, 1380 const char *buf, size_t count) 1381 { 1382 struct clocksource *cs; 1383 char name[CS_NAME_LEN]; 1384 ssize_t ret; 1385 1386 ret = sysfs_get_uname(buf, name, count); 1387 if (ret < 0) 1388 return ret; 1389 1390 ret = -ENODEV; 1391 mutex_lock(&clocksource_mutex); 1392 list_for_each_entry(cs, &clocksource_list, list) { 1393 if (strcmp(cs->name, name)) 1394 continue; 1395 ret = clocksource_unbind(cs); 1396 break; 1397 } 1398 mutex_unlock(&clocksource_mutex); 1399 1400 return ret ? ret : count; 1401 } 1402 static DEVICE_ATTR_WO(unbind_clocksource); 1403 1404 /** 1405 * available_clocksource_show - sysfs interface for listing clocksource 1406 * @dev: unused 1407 * @attr: unused 1408 * @buf: char buffer to be filled with clocksource list 1409 * 1410 * Provides sysfs interface for listing registered clocksources 1411 */ 1412 static ssize_t available_clocksource_show(struct device *dev, 1413 struct device_attribute *attr, 1414 char *buf) 1415 { 1416 struct clocksource *src; 1417 ssize_t count = 0; 1418 1419 mutex_lock(&clocksource_mutex); 1420 list_for_each_entry(src, &clocksource_list, list) { 1421 /* 1422 * Don't show non-HRES clocksource if the tick code is 1423 * in one shot mode (highres=on or nohz=on) 1424 */ 1425 if (!tick_oneshot_mode_active() || 1426 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 1427 count += snprintf(buf + count, 1428 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), 1429 "%s ", src->name); 1430 } 1431 mutex_unlock(&clocksource_mutex); 1432 1433 count += snprintf(buf + count, 1434 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n"); 1435 1436 return count; 1437 } 1438 static DEVICE_ATTR_RO(available_clocksource); 1439 1440 static struct attribute *clocksource_attrs[] = { 1441 &dev_attr_current_clocksource.attr, 1442 &dev_attr_unbind_clocksource.attr, 1443 &dev_attr_available_clocksource.attr, 1444 NULL 1445 }; 1446 ATTRIBUTE_GROUPS(clocksource); 1447 1448 static struct bus_type clocksource_subsys = { 1449 .name = "clocksource", 1450 .dev_name = "clocksource", 1451 }; 1452 1453 static struct device device_clocksource = { 1454 .id = 0, 1455 .bus = &clocksource_subsys, 1456 .groups = clocksource_groups, 1457 }; 1458 1459 static int __init init_clocksource_sysfs(void) 1460 { 1461 int error = subsys_system_register(&clocksource_subsys, NULL); 1462 1463 if (!error) 1464 error = device_register(&device_clocksource); 1465 1466 return error; 1467 } 1468 1469 device_initcall(init_clocksource_sysfs); 1470 #endif /* CONFIG_SYSFS */ 1471 1472 /** 1473 * boot_override_clocksource - boot clock override 1474 * @str: override name 1475 * 1476 * Takes a clocksource= boot argument and uses it 1477 * as the clocksource override name. 1478 */ 1479 static int __init boot_override_clocksource(char* str) 1480 { 1481 mutex_lock(&clocksource_mutex); 1482 if (str) 1483 strscpy(override_name, str, sizeof(override_name)); 1484 mutex_unlock(&clocksource_mutex); 1485 return 1; 1486 } 1487 1488 __setup("clocksource=", boot_override_clocksource); 1489 1490 /** 1491 * boot_override_clock - Compatibility layer for deprecated boot option 1492 * @str: override name 1493 * 1494 * DEPRECATED! Takes a clock= boot argument and uses it 1495 * as the clocksource override name 1496 */ 1497 static int __init boot_override_clock(char* str) 1498 { 1499 if (!strcmp(str, "pmtmr")) { 1500 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n"); 1501 return boot_override_clocksource("acpi_pm"); 1502 } 1503 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n"); 1504 return boot_override_clocksource(str); 1505 } 1506 1507 __setup("clock=", boot_override_clock); 1508