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 * Threshold: 0.0312s, when doubled: 0.0625s. 100 * Also a default for cs->uncertainty_margin when registering clocks. 101 */ 102 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 5) 103 104 /* 105 * Maximum permissible delay between two readouts of the watchdog 106 * clocksource surrounding a read of the clocksource being validated. 107 * This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as 108 * a lower bound for cs->uncertainty_margin values when registering clocks. 109 */ 110 #define WATCHDOG_MAX_SKEW (50 * NSEC_PER_USEC) 111 112 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG 113 static void clocksource_watchdog_work(struct work_struct *work); 114 static void clocksource_select(void); 115 116 static LIST_HEAD(watchdog_list); 117 static struct clocksource *watchdog; 118 static struct timer_list watchdog_timer; 119 static DECLARE_WORK(watchdog_work, clocksource_watchdog_work); 120 static DEFINE_SPINLOCK(watchdog_lock); 121 static int watchdog_running; 122 static atomic_t watchdog_reset_pending; 123 124 static inline void clocksource_watchdog_lock(unsigned long *flags) 125 { 126 spin_lock_irqsave(&watchdog_lock, *flags); 127 } 128 129 static inline void clocksource_watchdog_unlock(unsigned long *flags) 130 { 131 spin_unlock_irqrestore(&watchdog_lock, *flags); 132 } 133 134 static int clocksource_watchdog_kthread(void *data); 135 static void __clocksource_change_rating(struct clocksource *cs, int rating); 136 137 /* 138 * Interval: 0.5sec. 139 */ 140 #define WATCHDOG_INTERVAL (HZ >> 1) 141 142 static void clocksource_watchdog_work(struct work_struct *work) 143 { 144 /* 145 * We cannot directly run clocksource_watchdog_kthread() here, because 146 * clocksource_select() calls timekeeping_notify() which uses 147 * stop_machine(). One cannot use stop_machine() from a workqueue() due 148 * lock inversions wrt CPU hotplug. 149 * 150 * Also, we only ever run this work once or twice during the lifetime 151 * of the kernel, so there is no point in creating a more permanent 152 * kthread for this. 153 * 154 * If kthread_run fails the next watchdog scan over the 155 * watchdog_list will find the unstable clock again. 156 */ 157 kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog"); 158 } 159 160 static void __clocksource_unstable(struct clocksource *cs) 161 { 162 cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG); 163 cs->flags |= CLOCK_SOURCE_UNSTABLE; 164 165 /* 166 * If the clocksource is registered clocksource_watchdog_kthread() will 167 * re-rate and re-select. 168 */ 169 if (list_empty(&cs->list)) { 170 cs->rating = 0; 171 return; 172 } 173 174 if (cs->mark_unstable) 175 cs->mark_unstable(cs); 176 177 /* kick clocksource_watchdog_kthread() */ 178 if (finished_booting) 179 schedule_work(&watchdog_work); 180 } 181 182 /** 183 * clocksource_mark_unstable - mark clocksource unstable via watchdog 184 * @cs: clocksource to be marked unstable 185 * 186 * This function is called by the x86 TSC code to mark clocksources as unstable; 187 * it defers demotion and re-selection to a kthread. 188 */ 189 void clocksource_mark_unstable(struct clocksource *cs) 190 { 191 unsigned long flags; 192 193 spin_lock_irqsave(&watchdog_lock, flags); 194 if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) { 195 if (!list_empty(&cs->list) && list_empty(&cs->wd_list)) 196 list_add(&cs->wd_list, &watchdog_list); 197 __clocksource_unstable(cs); 198 } 199 spin_unlock_irqrestore(&watchdog_lock, flags); 200 } 201 202 ulong max_cswd_read_retries = 3; 203 module_param(max_cswd_read_retries, ulong, 0644); 204 EXPORT_SYMBOL_GPL(max_cswd_read_retries); 205 static int verify_n_cpus = 8; 206 module_param(verify_n_cpus, int, 0644); 207 208 static bool cs_watchdog_read(struct clocksource *cs, u64 *csnow, u64 *wdnow) 209 { 210 unsigned int nretries; 211 u64 wd_end, wd_delta; 212 int64_t wd_delay; 213 214 for (nretries = 0; nretries <= max_cswd_read_retries; nretries++) { 215 local_irq_disable(); 216 *wdnow = watchdog->read(watchdog); 217 *csnow = cs->read(cs); 218 wd_end = watchdog->read(watchdog); 219 local_irq_enable(); 220 221 wd_delta = clocksource_delta(wd_end, *wdnow, watchdog->mask); 222 wd_delay = clocksource_cyc2ns(wd_delta, watchdog->mult, 223 watchdog->shift); 224 if (wd_delay <= WATCHDOG_MAX_SKEW) { 225 if (nretries > 1 || nretries >= max_cswd_read_retries) { 226 pr_warn("timekeeping watchdog on CPU%d: %s retried %d times before success\n", 227 smp_processor_id(), watchdog->name, nretries); 228 } 229 return true; 230 } 231 } 232 233 pr_warn("timekeeping watchdog on CPU%d: %s read-back delay of %lldns, attempt %d, marking unstable\n", 234 smp_processor_id(), watchdog->name, wd_delay, nretries); 235 return false; 236 } 237 238 static u64 csnow_mid; 239 static cpumask_t cpus_ahead; 240 static cpumask_t cpus_behind; 241 static cpumask_t cpus_chosen; 242 243 static void clocksource_verify_choose_cpus(void) 244 { 245 int cpu, i, n = verify_n_cpus; 246 247 if (n < 0) { 248 /* Check all of the CPUs. */ 249 cpumask_copy(&cpus_chosen, cpu_online_mask); 250 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); 251 return; 252 } 253 254 /* If no checking desired, or no other CPU to check, leave. */ 255 cpumask_clear(&cpus_chosen); 256 if (n == 0 || num_online_cpus() <= 1) 257 return; 258 259 /* Make sure to select at least one CPU other than the current CPU. */ 260 cpu = cpumask_next(-1, cpu_online_mask); 261 if (cpu == smp_processor_id()) 262 cpu = cpumask_next(cpu, cpu_online_mask); 263 if (WARN_ON_ONCE(cpu >= nr_cpu_ids)) 264 return; 265 cpumask_set_cpu(cpu, &cpus_chosen); 266 267 /* Force a sane value for the boot parameter. */ 268 if (n > nr_cpu_ids) 269 n = nr_cpu_ids; 270 271 /* 272 * Randomly select the specified number of CPUs. If the same 273 * CPU is selected multiple times, that CPU is checked only once, 274 * and no replacement CPU is selected. This gracefully handles 275 * situations where verify_n_cpus is greater than the number of 276 * CPUs that are currently online. 277 */ 278 for (i = 1; i < n; i++) { 279 cpu = prandom_u32() % nr_cpu_ids; 280 cpu = cpumask_next(cpu - 1, cpu_online_mask); 281 if (cpu >= nr_cpu_ids) 282 cpu = cpumask_next(-1, cpu_online_mask); 283 if (!WARN_ON_ONCE(cpu >= nr_cpu_ids)) 284 cpumask_set_cpu(cpu, &cpus_chosen); 285 } 286 287 /* Don't verify ourselves. */ 288 cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); 289 } 290 291 static void clocksource_verify_one_cpu(void *csin) 292 { 293 struct clocksource *cs = (struct clocksource *)csin; 294 295 csnow_mid = cs->read(cs); 296 } 297 298 void clocksource_verify_percpu(struct clocksource *cs) 299 { 300 int64_t cs_nsec, cs_nsec_max = 0, cs_nsec_min = LLONG_MAX; 301 u64 csnow_begin, csnow_end; 302 int cpu, testcpu; 303 s64 delta; 304 305 if (verify_n_cpus == 0) 306 return; 307 cpumask_clear(&cpus_ahead); 308 cpumask_clear(&cpus_behind); 309 cpus_read_lock(); 310 preempt_disable(); 311 clocksource_verify_choose_cpus(); 312 if (cpumask_weight(&cpus_chosen) == 0) { 313 preempt_enable(); 314 cpus_read_unlock(); 315 pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name); 316 return; 317 } 318 testcpu = smp_processor_id(); 319 pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen)); 320 for_each_cpu(cpu, &cpus_chosen) { 321 if (cpu == testcpu) 322 continue; 323 csnow_begin = cs->read(cs); 324 smp_call_function_single(cpu, clocksource_verify_one_cpu, cs, 1); 325 csnow_end = cs->read(cs); 326 delta = (s64)((csnow_mid - csnow_begin) & cs->mask); 327 if (delta < 0) 328 cpumask_set_cpu(cpu, &cpus_behind); 329 delta = (csnow_end - csnow_mid) & cs->mask; 330 if (delta < 0) 331 cpumask_set_cpu(cpu, &cpus_ahead); 332 delta = clocksource_delta(csnow_end, csnow_begin, cs->mask); 333 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift); 334 if (cs_nsec > cs_nsec_max) 335 cs_nsec_max = cs_nsec; 336 if (cs_nsec < cs_nsec_min) 337 cs_nsec_min = cs_nsec; 338 } 339 preempt_enable(); 340 cpus_read_unlock(); 341 if (!cpumask_empty(&cpus_ahead)) 342 pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n", 343 cpumask_pr_args(&cpus_ahead), testcpu, cs->name); 344 if (!cpumask_empty(&cpus_behind)) 345 pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n", 346 cpumask_pr_args(&cpus_behind), testcpu, cs->name); 347 if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind)) 348 pr_warn(" CPU %d check durations %lldns - %lldns for clocksource %s.\n", 349 testcpu, cs_nsec_min, cs_nsec_max, cs->name); 350 } 351 EXPORT_SYMBOL_GPL(clocksource_verify_percpu); 352 353 static void clocksource_watchdog(struct timer_list *unused) 354 { 355 u64 csnow, wdnow, cslast, wdlast, delta; 356 int next_cpu, reset_pending; 357 int64_t wd_nsec, cs_nsec; 358 struct clocksource *cs; 359 u32 md; 360 361 spin_lock(&watchdog_lock); 362 if (!watchdog_running) 363 goto out; 364 365 reset_pending = atomic_read(&watchdog_reset_pending); 366 367 list_for_each_entry(cs, &watchdog_list, wd_list) { 368 369 /* Clocksource already marked unstable? */ 370 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 371 if (finished_booting) 372 schedule_work(&watchdog_work); 373 continue; 374 } 375 376 if (!cs_watchdog_read(cs, &csnow, &wdnow)) { 377 /* Clock readout unreliable, so give it up. */ 378 __clocksource_unstable(cs); 379 continue; 380 } 381 382 /* Clocksource initialized ? */ 383 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) || 384 atomic_read(&watchdog_reset_pending)) { 385 cs->flags |= CLOCK_SOURCE_WATCHDOG; 386 cs->wd_last = wdnow; 387 cs->cs_last = csnow; 388 continue; 389 } 390 391 delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask); 392 wd_nsec = clocksource_cyc2ns(delta, watchdog->mult, 393 watchdog->shift); 394 395 delta = clocksource_delta(csnow, cs->cs_last, cs->mask); 396 cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift); 397 wdlast = cs->wd_last; /* save these in case we print them */ 398 cslast = cs->cs_last; 399 cs->cs_last = csnow; 400 cs->wd_last = wdnow; 401 402 if (atomic_read(&watchdog_reset_pending)) 403 continue; 404 405 /* Check the deviation from the watchdog clocksource. */ 406 md = cs->uncertainty_margin + watchdog->uncertainty_margin; 407 if (abs(cs_nsec - wd_nsec) > md) { 408 pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n", 409 smp_processor_id(), cs->name); 410 pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n", 411 watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask); 412 pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n", 413 cs->name, cs_nsec, csnow, cslast, cs->mask); 414 if (curr_clocksource == cs) 415 pr_warn(" '%s' is current clocksource.\n", cs->name); 416 else if (curr_clocksource) 417 pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name); 418 else 419 pr_warn(" No current clocksource.\n"); 420 __clocksource_unstable(cs); 421 continue; 422 } 423 424 if (cs == curr_clocksource && cs->tick_stable) 425 cs->tick_stable(cs); 426 427 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && 428 (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) && 429 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) { 430 /* Mark it valid for high-res. */ 431 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 432 433 /* 434 * clocksource_done_booting() will sort it if 435 * finished_booting is not set yet. 436 */ 437 if (!finished_booting) 438 continue; 439 440 /* 441 * If this is not the current clocksource let 442 * the watchdog thread reselect it. Due to the 443 * change to high res this clocksource might 444 * be preferred now. If it is the current 445 * clocksource let the tick code know about 446 * that change. 447 */ 448 if (cs != curr_clocksource) { 449 cs->flags |= CLOCK_SOURCE_RESELECT; 450 schedule_work(&watchdog_work); 451 } else { 452 tick_clock_notify(); 453 } 454 } 455 } 456 457 /* 458 * We only clear the watchdog_reset_pending, when we did a 459 * full cycle through all clocksources. 460 */ 461 if (reset_pending) 462 atomic_dec(&watchdog_reset_pending); 463 464 /* 465 * Cycle through CPUs to check if the CPUs stay synchronized 466 * to each other. 467 */ 468 next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask); 469 if (next_cpu >= nr_cpu_ids) 470 next_cpu = cpumask_first(cpu_online_mask); 471 472 /* 473 * Arm timer if not already pending: could race with concurrent 474 * pair clocksource_stop_watchdog() clocksource_start_watchdog(). 475 */ 476 if (!timer_pending(&watchdog_timer)) { 477 watchdog_timer.expires += WATCHDOG_INTERVAL; 478 add_timer_on(&watchdog_timer, next_cpu); 479 } 480 out: 481 spin_unlock(&watchdog_lock); 482 } 483 484 static inline void clocksource_start_watchdog(void) 485 { 486 if (watchdog_running || !watchdog || list_empty(&watchdog_list)) 487 return; 488 timer_setup(&watchdog_timer, clocksource_watchdog, 0); 489 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL; 490 add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask)); 491 watchdog_running = 1; 492 } 493 494 static inline void clocksource_stop_watchdog(void) 495 { 496 if (!watchdog_running || (watchdog && !list_empty(&watchdog_list))) 497 return; 498 del_timer(&watchdog_timer); 499 watchdog_running = 0; 500 } 501 502 static inline void clocksource_reset_watchdog(void) 503 { 504 struct clocksource *cs; 505 506 list_for_each_entry(cs, &watchdog_list, wd_list) 507 cs->flags &= ~CLOCK_SOURCE_WATCHDOG; 508 } 509 510 static void clocksource_resume_watchdog(void) 511 { 512 atomic_inc(&watchdog_reset_pending); 513 } 514 515 static void clocksource_enqueue_watchdog(struct clocksource *cs) 516 { 517 INIT_LIST_HEAD(&cs->wd_list); 518 519 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { 520 /* cs is a clocksource to be watched. */ 521 list_add(&cs->wd_list, &watchdog_list); 522 cs->flags &= ~CLOCK_SOURCE_WATCHDOG; 523 } else { 524 /* cs is a watchdog. */ 525 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 526 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 527 } 528 } 529 530 static void clocksource_select_watchdog(bool fallback) 531 { 532 struct clocksource *cs, *old_wd; 533 unsigned long flags; 534 535 spin_lock_irqsave(&watchdog_lock, flags); 536 /* save current watchdog */ 537 old_wd = watchdog; 538 if (fallback) 539 watchdog = NULL; 540 541 list_for_each_entry(cs, &clocksource_list, list) { 542 /* cs is a clocksource to be watched. */ 543 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) 544 continue; 545 546 /* Skip current if we were requested for a fallback. */ 547 if (fallback && cs == old_wd) 548 continue; 549 550 /* Pick the best watchdog. */ 551 if (!watchdog || cs->rating > watchdog->rating) 552 watchdog = cs; 553 } 554 /* If we failed to find a fallback restore the old one. */ 555 if (!watchdog) 556 watchdog = old_wd; 557 558 /* If we changed the watchdog we need to reset cycles. */ 559 if (watchdog != old_wd) 560 clocksource_reset_watchdog(); 561 562 /* Check if the watchdog timer needs to be started. */ 563 clocksource_start_watchdog(); 564 spin_unlock_irqrestore(&watchdog_lock, flags); 565 } 566 567 static void clocksource_dequeue_watchdog(struct clocksource *cs) 568 { 569 if (cs != watchdog) { 570 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { 571 /* cs is a watched clocksource. */ 572 list_del_init(&cs->wd_list); 573 /* Check if the watchdog timer needs to be stopped. */ 574 clocksource_stop_watchdog(); 575 } 576 } 577 } 578 579 static int __clocksource_watchdog_kthread(void) 580 { 581 struct clocksource *cs, *tmp; 582 unsigned long flags; 583 int select = 0; 584 585 /* Do any required per-CPU skew verification. */ 586 if (curr_clocksource && 587 curr_clocksource->flags & CLOCK_SOURCE_UNSTABLE && 588 curr_clocksource->flags & CLOCK_SOURCE_VERIFY_PERCPU) 589 clocksource_verify_percpu(curr_clocksource); 590 591 spin_lock_irqsave(&watchdog_lock, flags); 592 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) { 593 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 594 list_del_init(&cs->wd_list); 595 __clocksource_change_rating(cs, 0); 596 select = 1; 597 } 598 if (cs->flags & CLOCK_SOURCE_RESELECT) { 599 cs->flags &= ~CLOCK_SOURCE_RESELECT; 600 select = 1; 601 } 602 } 603 /* Check if the watchdog timer needs to be stopped. */ 604 clocksource_stop_watchdog(); 605 spin_unlock_irqrestore(&watchdog_lock, flags); 606 607 return select; 608 } 609 610 static int clocksource_watchdog_kthread(void *data) 611 { 612 mutex_lock(&clocksource_mutex); 613 if (__clocksource_watchdog_kthread()) 614 clocksource_select(); 615 mutex_unlock(&clocksource_mutex); 616 return 0; 617 } 618 619 static bool clocksource_is_watchdog(struct clocksource *cs) 620 { 621 return cs == watchdog; 622 } 623 624 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */ 625 626 static void clocksource_enqueue_watchdog(struct clocksource *cs) 627 { 628 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 629 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 630 } 631 632 static void clocksource_select_watchdog(bool fallback) { } 633 static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { } 634 static inline void clocksource_resume_watchdog(void) { } 635 static inline int __clocksource_watchdog_kthread(void) { return 0; } 636 static bool clocksource_is_watchdog(struct clocksource *cs) { return false; } 637 void clocksource_mark_unstable(struct clocksource *cs) { } 638 639 static inline void clocksource_watchdog_lock(unsigned long *flags) { } 640 static inline void clocksource_watchdog_unlock(unsigned long *flags) { } 641 642 #endif /* CONFIG_CLOCKSOURCE_WATCHDOG */ 643 644 static bool clocksource_is_suspend(struct clocksource *cs) 645 { 646 return cs == suspend_clocksource; 647 } 648 649 static void __clocksource_suspend_select(struct clocksource *cs) 650 { 651 /* 652 * Skip the clocksource which will be stopped in suspend state. 653 */ 654 if (!(cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP)) 655 return; 656 657 /* 658 * The nonstop clocksource can be selected as the suspend clocksource to 659 * calculate the suspend time, so it should not supply suspend/resume 660 * interfaces to suspend the nonstop clocksource when system suspends. 661 */ 662 if (cs->suspend || cs->resume) { 663 pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n", 664 cs->name); 665 } 666 667 /* Pick the best rating. */ 668 if (!suspend_clocksource || cs->rating > suspend_clocksource->rating) 669 suspend_clocksource = cs; 670 } 671 672 /** 673 * clocksource_suspend_select - Select the best clocksource for suspend timing 674 * @fallback: if select a fallback clocksource 675 */ 676 static void clocksource_suspend_select(bool fallback) 677 { 678 struct clocksource *cs, *old_suspend; 679 680 old_suspend = suspend_clocksource; 681 if (fallback) 682 suspend_clocksource = NULL; 683 684 list_for_each_entry(cs, &clocksource_list, list) { 685 /* Skip current if we were requested for a fallback. */ 686 if (fallback && cs == old_suspend) 687 continue; 688 689 __clocksource_suspend_select(cs); 690 } 691 } 692 693 /** 694 * clocksource_start_suspend_timing - Start measuring the suspend timing 695 * @cs: current clocksource from timekeeping 696 * @start_cycles: current cycles from timekeeping 697 * 698 * This function will save the start cycle values of suspend timer to calculate 699 * the suspend time when resuming system. 700 * 701 * This function is called late in the suspend process from timekeeping_suspend(), 702 * that means processes are frozen, non-boot cpus and interrupts are disabled 703 * now. It is therefore possible to start the suspend timer without taking the 704 * clocksource mutex. 705 */ 706 void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles) 707 { 708 if (!suspend_clocksource) 709 return; 710 711 /* 712 * If current clocksource is the suspend timer, we should use the 713 * tkr_mono.cycle_last value as suspend_start to avoid same reading 714 * from suspend timer. 715 */ 716 if (clocksource_is_suspend(cs)) { 717 suspend_start = start_cycles; 718 return; 719 } 720 721 if (suspend_clocksource->enable && 722 suspend_clocksource->enable(suspend_clocksource)) { 723 pr_warn_once("Failed to enable the non-suspend-able clocksource.\n"); 724 return; 725 } 726 727 suspend_start = suspend_clocksource->read(suspend_clocksource); 728 } 729 730 /** 731 * clocksource_stop_suspend_timing - Stop measuring the suspend timing 732 * @cs: current clocksource from timekeeping 733 * @cycle_now: current cycles from timekeeping 734 * 735 * This function will calculate the suspend time from suspend timer. 736 * 737 * Returns nanoseconds since suspend started, 0 if no usable suspend clocksource. 738 * 739 * This function is called early in the resume process from timekeeping_resume(), 740 * that means there is only one cpu, no processes are running and the interrupts 741 * are disabled. It is therefore possible to stop the suspend timer without 742 * taking the clocksource mutex. 743 */ 744 u64 clocksource_stop_suspend_timing(struct clocksource *cs, u64 cycle_now) 745 { 746 u64 now, delta, nsec = 0; 747 748 if (!suspend_clocksource) 749 return 0; 750 751 /* 752 * If current clocksource is the suspend timer, we should use the 753 * tkr_mono.cycle_last value from timekeeping as current cycle to 754 * avoid same reading from suspend timer. 755 */ 756 if (clocksource_is_suspend(cs)) 757 now = cycle_now; 758 else 759 now = suspend_clocksource->read(suspend_clocksource); 760 761 if (now > suspend_start) { 762 delta = clocksource_delta(now, suspend_start, 763 suspend_clocksource->mask); 764 nsec = mul_u64_u32_shr(delta, suspend_clocksource->mult, 765 suspend_clocksource->shift); 766 } 767 768 /* 769 * Disable the suspend timer to save power if current clocksource is 770 * not the suspend timer. 771 */ 772 if (!clocksource_is_suspend(cs) && suspend_clocksource->disable) 773 suspend_clocksource->disable(suspend_clocksource); 774 775 return nsec; 776 } 777 778 /** 779 * clocksource_suspend - suspend the clocksource(s) 780 */ 781 void clocksource_suspend(void) 782 { 783 struct clocksource *cs; 784 785 list_for_each_entry_reverse(cs, &clocksource_list, list) 786 if (cs->suspend) 787 cs->suspend(cs); 788 } 789 790 /** 791 * clocksource_resume - resume the clocksource(s) 792 */ 793 void clocksource_resume(void) 794 { 795 struct clocksource *cs; 796 797 list_for_each_entry(cs, &clocksource_list, list) 798 if (cs->resume) 799 cs->resume(cs); 800 801 clocksource_resume_watchdog(); 802 } 803 804 /** 805 * clocksource_touch_watchdog - Update watchdog 806 * 807 * Update the watchdog after exception contexts such as kgdb so as not 808 * to incorrectly trip the watchdog. This might fail when the kernel 809 * was stopped in code which holds watchdog_lock. 810 */ 811 void clocksource_touch_watchdog(void) 812 { 813 clocksource_resume_watchdog(); 814 } 815 816 /** 817 * clocksource_max_adjustment- Returns max adjustment amount 818 * @cs: Pointer to clocksource 819 * 820 */ 821 static u32 clocksource_max_adjustment(struct clocksource *cs) 822 { 823 u64 ret; 824 /* 825 * We won't try to correct for more than 11% adjustments (110,000 ppm), 826 */ 827 ret = (u64)cs->mult * 11; 828 do_div(ret,100); 829 return (u32)ret; 830 } 831 832 /** 833 * clocks_calc_max_nsecs - Returns maximum nanoseconds that can be converted 834 * @mult: cycle to nanosecond multiplier 835 * @shift: cycle to nanosecond divisor (power of two) 836 * @maxadj: maximum adjustment value to mult (~11%) 837 * @mask: bitmask for two's complement subtraction of non 64 bit counters 838 * @max_cyc: maximum cycle value before potential overflow (does not include 839 * any safety margin) 840 * 841 * NOTE: This function includes a safety margin of 50%, in other words, we 842 * return half the number of nanoseconds the hardware counter can technically 843 * cover. This is done so that we can potentially detect problems caused by 844 * delayed timers or bad hardware, which might result in time intervals that 845 * are larger than what the math used can handle without overflows. 846 */ 847 u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc) 848 { 849 u64 max_nsecs, max_cycles; 850 851 /* 852 * Calculate the maximum number of cycles that we can pass to the 853 * cyc2ns() function without overflowing a 64-bit result. 854 */ 855 max_cycles = ULLONG_MAX; 856 do_div(max_cycles, mult+maxadj); 857 858 /* 859 * The actual maximum number of cycles we can defer the clocksource is 860 * determined by the minimum of max_cycles and mask. 861 * Note: Here we subtract the maxadj to make sure we don't sleep for 862 * too long if there's a large negative adjustment. 863 */ 864 max_cycles = min(max_cycles, mask); 865 max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift); 866 867 /* return the max_cycles value as well if requested */ 868 if (max_cyc) 869 *max_cyc = max_cycles; 870 871 /* Return 50% of the actual maximum, so we can detect bad values */ 872 max_nsecs >>= 1; 873 874 return max_nsecs; 875 } 876 877 /** 878 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles 879 * @cs: Pointer to clocksource to be updated 880 * 881 */ 882 static inline void clocksource_update_max_deferment(struct clocksource *cs) 883 { 884 cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift, 885 cs->maxadj, cs->mask, 886 &cs->max_cycles); 887 } 888 889 static struct clocksource *clocksource_find_best(bool oneshot, bool skipcur) 890 { 891 struct clocksource *cs; 892 893 if (!finished_booting || list_empty(&clocksource_list)) 894 return NULL; 895 896 /* 897 * We pick the clocksource with the highest rating. If oneshot 898 * mode is active, we pick the highres valid clocksource with 899 * the best rating. 900 */ 901 list_for_each_entry(cs, &clocksource_list, list) { 902 if (skipcur && cs == curr_clocksource) 903 continue; 904 if (oneshot && !(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 905 continue; 906 return cs; 907 } 908 return NULL; 909 } 910 911 static void __clocksource_select(bool skipcur) 912 { 913 bool oneshot = tick_oneshot_mode_active(); 914 struct clocksource *best, *cs; 915 916 /* Find the best suitable clocksource */ 917 best = clocksource_find_best(oneshot, skipcur); 918 if (!best) 919 return; 920 921 if (!strlen(override_name)) 922 goto found; 923 924 /* Check for the override clocksource. */ 925 list_for_each_entry(cs, &clocksource_list, list) { 926 if (skipcur && cs == curr_clocksource) 927 continue; 928 if (strcmp(cs->name, override_name) != 0) 929 continue; 930 /* 931 * Check to make sure we don't switch to a non-highres 932 * capable clocksource if the tick code is in oneshot 933 * mode (highres or nohz) 934 */ 935 if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) && oneshot) { 936 /* Override clocksource cannot be used. */ 937 if (cs->flags & CLOCK_SOURCE_UNSTABLE) { 938 pr_warn("Override clocksource %s is unstable and not HRT compatible - cannot switch while in HRT/NOHZ mode\n", 939 cs->name); 940 override_name[0] = 0; 941 } else { 942 /* 943 * The override cannot be currently verified. 944 * Deferring to let the watchdog check. 945 */ 946 pr_info("Override clocksource %s is not currently HRT compatible - deferring\n", 947 cs->name); 948 } 949 } else 950 /* Override clocksource can be used. */ 951 best = cs; 952 break; 953 } 954 955 found: 956 if (curr_clocksource != best && !timekeeping_notify(best)) { 957 pr_info("Switched to clocksource %s\n", best->name); 958 curr_clocksource = best; 959 } 960 } 961 962 /** 963 * clocksource_select - Select the best clocksource available 964 * 965 * Private function. Must hold clocksource_mutex when called. 966 * 967 * Select the clocksource with the best rating, or the clocksource, 968 * which is selected by userspace override. 969 */ 970 static void clocksource_select(void) 971 { 972 __clocksource_select(false); 973 } 974 975 static void clocksource_select_fallback(void) 976 { 977 __clocksource_select(true); 978 } 979 980 /* 981 * clocksource_done_booting - Called near the end of core bootup 982 * 983 * Hack to avoid lots of clocksource churn at boot time. 984 * We use fs_initcall because we want this to start before 985 * device_initcall but after subsys_initcall. 986 */ 987 static int __init clocksource_done_booting(void) 988 { 989 mutex_lock(&clocksource_mutex); 990 curr_clocksource = clocksource_default_clock(); 991 finished_booting = 1; 992 /* 993 * Run the watchdog first to eliminate unstable clock sources 994 */ 995 __clocksource_watchdog_kthread(); 996 clocksource_select(); 997 mutex_unlock(&clocksource_mutex); 998 return 0; 999 } 1000 fs_initcall(clocksource_done_booting); 1001 1002 /* 1003 * Enqueue the clocksource sorted by rating 1004 */ 1005 static void clocksource_enqueue(struct clocksource *cs) 1006 { 1007 struct list_head *entry = &clocksource_list; 1008 struct clocksource *tmp; 1009 1010 list_for_each_entry(tmp, &clocksource_list, list) { 1011 /* Keep track of the place, where to insert */ 1012 if (tmp->rating < cs->rating) 1013 break; 1014 entry = &tmp->list; 1015 } 1016 list_add(&cs->list, entry); 1017 } 1018 1019 /** 1020 * __clocksource_update_freq_scale - Used update clocksource with new freq 1021 * @cs: clocksource to be registered 1022 * @scale: Scale factor multiplied against freq to get clocksource hz 1023 * @freq: clocksource frequency (cycles per second) divided by scale 1024 * 1025 * This should only be called from the clocksource->enable() method. 1026 * 1027 * This *SHOULD NOT* be called directly! Please use the 1028 * __clocksource_update_freq_hz() or __clocksource_update_freq_khz() helper 1029 * functions. 1030 */ 1031 void __clocksource_update_freq_scale(struct clocksource *cs, u32 scale, u32 freq) 1032 { 1033 u64 sec; 1034 1035 /* 1036 * Default clocksources are *special* and self-define their mult/shift. 1037 * But, you're not special, so you should specify a freq value. 1038 */ 1039 if (freq) { 1040 /* 1041 * Calc the maximum number of seconds which we can run before 1042 * wrapping around. For clocksources which have a mask > 32-bit 1043 * we need to limit the max sleep time to have a good 1044 * conversion precision. 10 minutes is still a reasonable 1045 * amount. That results in a shift value of 24 for a 1046 * clocksource with mask >= 40-bit and f >= 4GHz. That maps to 1047 * ~ 0.06ppm granularity for NTP. 1048 */ 1049 sec = cs->mask; 1050 do_div(sec, freq); 1051 do_div(sec, scale); 1052 if (!sec) 1053 sec = 1; 1054 else if (sec > 600 && cs->mask > UINT_MAX) 1055 sec = 600; 1056 1057 clocks_calc_mult_shift(&cs->mult, &cs->shift, freq, 1058 NSEC_PER_SEC / scale, sec * scale); 1059 } 1060 1061 /* 1062 * If the uncertainty margin is not specified, calculate it. 1063 * If both scale and freq are non-zero, calculate the clock 1064 * period, but bound below at 2*WATCHDOG_MAX_SKEW. However, 1065 * if either of scale or freq is zero, be very conservative and 1066 * take the tens-of-milliseconds WATCHDOG_THRESHOLD value for the 1067 * uncertainty margin. Allow stupidly small uncertainty margins 1068 * to be specified by the caller for testing purposes, but warn 1069 * to discourage production use of this capability. 1070 */ 1071 if (scale && freq && !cs->uncertainty_margin) { 1072 cs->uncertainty_margin = NSEC_PER_SEC / (scale * freq); 1073 if (cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW) 1074 cs->uncertainty_margin = 2 * WATCHDOG_MAX_SKEW; 1075 } else if (!cs->uncertainty_margin) { 1076 cs->uncertainty_margin = WATCHDOG_THRESHOLD; 1077 } 1078 WARN_ON_ONCE(cs->uncertainty_margin < 2 * WATCHDOG_MAX_SKEW); 1079 1080 /* 1081 * Ensure clocksources that have large 'mult' values don't overflow 1082 * when adjusted. 1083 */ 1084 cs->maxadj = clocksource_max_adjustment(cs); 1085 while (freq && ((cs->mult + cs->maxadj < cs->mult) 1086 || (cs->mult - cs->maxadj > cs->mult))) { 1087 cs->mult >>= 1; 1088 cs->shift--; 1089 cs->maxadj = clocksource_max_adjustment(cs); 1090 } 1091 1092 /* 1093 * Only warn for *special* clocksources that self-define 1094 * their mult/shift values and don't specify a freq. 1095 */ 1096 WARN_ONCE(cs->mult + cs->maxadj < cs->mult, 1097 "timekeeping: Clocksource %s might overflow on 11%% adjustment\n", 1098 cs->name); 1099 1100 clocksource_update_max_deferment(cs); 1101 1102 pr_info("%s: mask: 0x%llx max_cycles: 0x%llx, max_idle_ns: %lld ns\n", 1103 cs->name, cs->mask, cs->max_cycles, cs->max_idle_ns); 1104 } 1105 EXPORT_SYMBOL_GPL(__clocksource_update_freq_scale); 1106 1107 /** 1108 * __clocksource_register_scale - Used to install new clocksources 1109 * @cs: clocksource to be registered 1110 * @scale: Scale factor multiplied against freq to get clocksource hz 1111 * @freq: clocksource frequency (cycles per second) divided by scale 1112 * 1113 * Returns -EBUSY if registration fails, zero otherwise. 1114 * 1115 * This *SHOULD NOT* be called directly! Please use the 1116 * clocksource_register_hz() or clocksource_register_khz helper functions. 1117 */ 1118 int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq) 1119 { 1120 unsigned long flags; 1121 1122 clocksource_arch_init(cs); 1123 1124 if (WARN_ON_ONCE((unsigned int)cs->id >= CSID_MAX)) 1125 cs->id = CSID_GENERIC; 1126 if (cs->vdso_clock_mode < 0 || 1127 cs->vdso_clock_mode >= VDSO_CLOCKMODE_MAX) { 1128 pr_warn("clocksource %s registered with invalid VDSO mode %d. Disabling VDSO support.\n", 1129 cs->name, cs->vdso_clock_mode); 1130 cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE; 1131 } 1132 1133 /* Initialize mult/shift and max_idle_ns */ 1134 __clocksource_update_freq_scale(cs, scale, freq); 1135 1136 /* Add clocksource to the clocksource list */ 1137 mutex_lock(&clocksource_mutex); 1138 1139 clocksource_watchdog_lock(&flags); 1140 clocksource_enqueue(cs); 1141 clocksource_enqueue_watchdog(cs); 1142 clocksource_watchdog_unlock(&flags); 1143 1144 clocksource_select(); 1145 clocksource_select_watchdog(false); 1146 __clocksource_suspend_select(cs); 1147 mutex_unlock(&clocksource_mutex); 1148 return 0; 1149 } 1150 EXPORT_SYMBOL_GPL(__clocksource_register_scale); 1151 1152 static void __clocksource_change_rating(struct clocksource *cs, int rating) 1153 { 1154 list_del(&cs->list); 1155 cs->rating = rating; 1156 clocksource_enqueue(cs); 1157 } 1158 1159 /** 1160 * clocksource_change_rating - Change the rating of a registered clocksource 1161 * @cs: clocksource to be changed 1162 * @rating: new rating 1163 */ 1164 void clocksource_change_rating(struct clocksource *cs, int rating) 1165 { 1166 unsigned long flags; 1167 1168 mutex_lock(&clocksource_mutex); 1169 clocksource_watchdog_lock(&flags); 1170 __clocksource_change_rating(cs, rating); 1171 clocksource_watchdog_unlock(&flags); 1172 1173 clocksource_select(); 1174 clocksource_select_watchdog(false); 1175 clocksource_suspend_select(false); 1176 mutex_unlock(&clocksource_mutex); 1177 } 1178 EXPORT_SYMBOL(clocksource_change_rating); 1179 1180 /* 1181 * Unbind clocksource @cs. Called with clocksource_mutex held 1182 */ 1183 static int clocksource_unbind(struct clocksource *cs) 1184 { 1185 unsigned long flags; 1186 1187 if (clocksource_is_watchdog(cs)) { 1188 /* Select and try to install a replacement watchdog. */ 1189 clocksource_select_watchdog(true); 1190 if (clocksource_is_watchdog(cs)) 1191 return -EBUSY; 1192 } 1193 1194 if (cs == curr_clocksource) { 1195 /* Select and try to install a replacement clock source */ 1196 clocksource_select_fallback(); 1197 if (curr_clocksource == cs) 1198 return -EBUSY; 1199 } 1200 1201 if (clocksource_is_suspend(cs)) { 1202 /* 1203 * Select and try to install a replacement suspend clocksource. 1204 * If no replacement suspend clocksource, we will just let the 1205 * clocksource go and have no suspend clocksource. 1206 */ 1207 clocksource_suspend_select(true); 1208 } 1209 1210 clocksource_watchdog_lock(&flags); 1211 clocksource_dequeue_watchdog(cs); 1212 list_del_init(&cs->list); 1213 clocksource_watchdog_unlock(&flags); 1214 1215 return 0; 1216 } 1217 1218 /** 1219 * clocksource_unregister - remove a registered clocksource 1220 * @cs: clocksource to be unregistered 1221 */ 1222 int clocksource_unregister(struct clocksource *cs) 1223 { 1224 int ret = 0; 1225 1226 mutex_lock(&clocksource_mutex); 1227 if (!list_empty(&cs->list)) 1228 ret = clocksource_unbind(cs); 1229 mutex_unlock(&clocksource_mutex); 1230 return ret; 1231 } 1232 EXPORT_SYMBOL(clocksource_unregister); 1233 1234 #ifdef CONFIG_SYSFS 1235 /** 1236 * current_clocksource_show - sysfs interface for current clocksource 1237 * @dev: unused 1238 * @attr: unused 1239 * @buf: char buffer to be filled with clocksource list 1240 * 1241 * Provides sysfs interface for listing current clocksource. 1242 */ 1243 static ssize_t current_clocksource_show(struct device *dev, 1244 struct device_attribute *attr, 1245 char *buf) 1246 { 1247 ssize_t count = 0; 1248 1249 mutex_lock(&clocksource_mutex); 1250 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name); 1251 mutex_unlock(&clocksource_mutex); 1252 1253 return count; 1254 } 1255 1256 ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt) 1257 { 1258 size_t ret = cnt; 1259 1260 /* strings from sysfs write are not 0 terminated! */ 1261 if (!cnt || cnt >= CS_NAME_LEN) 1262 return -EINVAL; 1263 1264 /* strip of \n: */ 1265 if (buf[cnt-1] == '\n') 1266 cnt--; 1267 if (cnt > 0) 1268 memcpy(dst, buf, cnt); 1269 dst[cnt] = 0; 1270 return ret; 1271 } 1272 1273 /** 1274 * current_clocksource_store - interface for manually overriding clocksource 1275 * @dev: unused 1276 * @attr: unused 1277 * @buf: name of override clocksource 1278 * @count: length of buffer 1279 * 1280 * Takes input from sysfs interface for manually overriding the default 1281 * clocksource selection. 1282 */ 1283 static ssize_t current_clocksource_store(struct device *dev, 1284 struct device_attribute *attr, 1285 const char *buf, size_t count) 1286 { 1287 ssize_t ret; 1288 1289 mutex_lock(&clocksource_mutex); 1290 1291 ret = sysfs_get_uname(buf, override_name, count); 1292 if (ret >= 0) 1293 clocksource_select(); 1294 1295 mutex_unlock(&clocksource_mutex); 1296 1297 return ret; 1298 } 1299 static DEVICE_ATTR_RW(current_clocksource); 1300 1301 /** 1302 * unbind_clocksource_store - interface for manually unbinding clocksource 1303 * @dev: unused 1304 * @attr: unused 1305 * @buf: unused 1306 * @count: length of buffer 1307 * 1308 * Takes input from sysfs interface for manually unbinding a clocksource. 1309 */ 1310 static ssize_t unbind_clocksource_store(struct device *dev, 1311 struct device_attribute *attr, 1312 const char *buf, size_t count) 1313 { 1314 struct clocksource *cs; 1315 char name[CS_NAME_LEN]; 1316 ssize_t ret; 1317 1318 ret = sysfs_get_uname(buf, name, count); 1319 if (ret < 0) 1320 return ret; 1321 1322 ret = -ENODEV; 1323 mutex_lock(&clocksource_mutex); 1324 list_for_each_entry(cs, &clocksource_list, list) { 1325 if (strcmp(cs->name, name)) 1326 continue; 1327 ret = clocksource_unbind(cs); 1328 break; 1329 } 1330 mutex_unlock(&clocksource_mutex); 1331 1332 return ret ? ret : count; 1333 } 1334 static DEVICE_ATTR_WO(unbind_clocksource); 1335 1336 /** 1337 * available_clocksource_show - sysfs interface for listing clocksource 1338 * @dev: unused 1339 * @attr: unused 1340 * @buf: char buffer to be filled with clocksource list 1341 * 1342 * Provides sysfs interface for listing registered clocksources 1343 */ 1344 static ssize_t available_clocksource_show(struct device *dev, 1345 struct device_attribute *attr, 1346 char *buf) 1347 { 1348 struct clocksource *src; 1349 ssize_t count = 0; 1350 1351 mutex_lock(&clocksource_mutex); 1352 list_for_each_entry(src, &clocksource_list, list) { 1353 /* 1354 * Don't show non-HRES clocksource if the tick code is 1355 * in one shot mode (highres=on or nohz=on) 1356 */ 1357 if (!tick_oneshot_mode_active() || 1358 (src->flags & CLOCK_SOURCE_VALID_FOR_HRES)) 1359 count += snprintf(buf + count, 1360 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), 1361 "%s ", src->name); 1362 } 1363 mutex_unlock(&clocksource_mutex); 1364 1365 count += snprintf(buf + count, 1366 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n"); 1367 1368 return count; 1369 } 1370 static DEVICE_ATTR_RO(available_clocksource); 1371 1372 static struct attribute *clocksource_attrs[] = { 1373 &dev_attr_current_clocksource.attr, 1374 &dev_attr_unbind_clocksource.attr, 1375 &dev_attr_available_clocksource.attr, 1376 NULL 1377 }; 1378 ATTRIBUTE_GROUPS(clocksource); 1379 1380 static struct bus_type clocksource_subsys = { 1381 .name = "clocksource", 1382 .dev_name = "clocksource", 1383 }; 1384 1385 static struct device device_clocksource = { 1386 .id = 0, 1387 .bus = &clocksource_subsys, 1388 .groups = clocksource_groups, 1389 }; 1390 1391 static int __init init_clocksource_sysfs(void) 1392 { 1393 int error = subsys_system_register(&clocksource_subsys, NULL); 1394 1395 if (!error) 1396 error = device_register(&device_clocksource); 1397 1398 return error; 1399 } 1400 1401 device_initcall(init_clocksource_sysfs); 1402 #endif /* CONFIG_SYSFS */ 1403 1404 /** 1405 * boot_override_clocksource - boot clock override 1406 * @str: override name 1407 * 1408 * Takes a clocksource= boot argument and uses it 1409 * as the clocksource override name. 1410 */ 1411 static int __init boot_override_clocksource(char* str) 1412 { 1413 mutex_lock(&clocksource_mutex); 1414 if (str) 1415 strlcpy(override_name, str, sizeof(override_name)); 1416 mutex_unlock(&clocksource_mutex); 1417 return 1; 1418 } 1419 1420 __setup("clocksource=", boot_override_clocksource); 1421 1422 /** 1423 * boot_override_clock - Compatibility layer for deprecated boot option 1424 * @str: override name 1425 * 1426 * DEPRECATED! Takes a clock= boot argument and uses it 1427 * as the clocksource override name 1428 */ 1429 static int __init boot_override_clock(char* str) 1430 { 1431 if (!strcmp(str, "pmtmr")) { 1432 pr_warn("clock=pmtmr is deprecated - use clocksource=acpi_pm\n"); 1433 return boot_override_clocksource("acpi_pm"); 1434 } 1435 pr_warn("clock= boot option is deprecated - use clocksource=xyz\n"); 1436 return boot_override_clocksource(str); 1437 } 1438 1439 __setup("clock=", boot_override_clock); 1440