kernel/time/clocksource.c

   1 /*
   2  * linux/kernel/time/clocksource.c
   3  *
   4  * This file contains the functions which manage clocksource drivers.
   5  *
   6  * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  21  *
  22  * TODO WishList:
  23  *   o Allow clocksource drivers to be unregistered
  24  *   o get rid of clocksource_jiffies extern
  25  */
  26
  27 #include <linux/clocksource.h>
  28 #include <linux/sysdev.h>
  29 #include <linux/init.h>
  30 #include <linux/module.h>
  31 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
  32 #include <linux/tick.h>
  33
  34 /* XXX - Would like a better way for initializing curr_clocksource */
  35 extern struct clocksource clocksource_jiffies;
  36
  37 /*[Clocksource internal variables]---------
  38  * curr_clocksource:
  39  *      currently selected clocksource. Initialized to clocksource_jiffies.
  40  * next_clocksource:
  41  *      pending next selected clocksource.
  42  * clocksource_list:
  43  *      linked list with the registered clocksources
  44  * clocksource_lock:
  45  *      protects manipulations to curr_clocksource and next_clocksource
  46  *      and the clocksource_list
  47  * override_name:
  48  *      Name of the user-specified clocksource.
  49  */
  50 static struct clocksource *curr_clocksource = &clocksource_jiffies;
  51 static struct clocksource *next_clocksource;
  52 static struct clocksource *clocksource_override;
  53 static LIST_HEAD(clocksource_list);
  54 static DEFINE_SPINLOCK(clocksource_lock);
  55 static char override_name[32];
  56 static int finished_booting;
  57
  58 /* clocksource_done_booting - Called near the end of core bootup
  59  *
  60  * Hack to avoid lots of clocksource churn at boot time.
  61  * We use fs_initcall because we want this to start before
  62  * device_initcall but after subsys_initcall.
  63  */
  64 static int __init clocksource_done_booting(void)
  65 {
  66         finished_booting = 1;
  67         return 0;
  68 }
  69 fs_initcall(clocksource_done_booting);
  70
  71 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
  72 static LIST_HEAD(watchdog_list);
  73 static struct clocksource *watchdog;
  74 static struct timer_list watchdog_timer;
  75 static DEFINE_SPINLOCK(watchdog_lock);
  76 static cycle_t watchdog_last;
  77 static unsigned long watchdog_resumed;
  78
  79 /*
  80  * Interval: 0.5sec Threshold: 0.0625s
  81  */
  82 #define WATCHDOG_INTERVAL (HZ >> 1)
  83 #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
  84
  85 static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
  86 {
  87         if (delta > -WATCHDOG_THRESHOLD && delta < WATCHDOG_THRESHOLD)
  88                 return;
  89
  90         printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
  91                cs->name, delta);
  92         cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
  93         clocksource_change_rating(cs, 0);
  94         list_del(&cs->wd_list);
  95 }
  96
  97 static void clocksource_watchdog(unsigned long data)
  98 {
  99         struct clocksource *cs, *tmp;
 100         cycle_t csnow, wdnow;
 101         int64_t wd_nsec, cs_nsec;
 102         int resumed;
 103
 104         spin_lock(&watchdog_lock);
 105
 106         resumed = test_and_clear_bit(0, &watchdog_resumed);
 107
 108         wdnow = watchdog->read();
 109         wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
 110         watchdog_last = wdnow;
 111
 112         list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
 113                 csnow = cs->read();
 114
 115                 if (unlikely(resumed)) {
 116                         cs->wd_last = csnow;
 117                         continue;
 118                 }
 119
 120                 /* Initialized ? */
 121                 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
 122                         if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
 123                             (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
 124                                 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 125                                 /*
 126                                  * We just marked the clocksource as
 127                                  * highres-capable, notify the rest of the
 128                                  * system as well so that we transition
 129                                  * into high-res mode:
 130                                  */
 131                                 tick_clock_notify();
 132                         }
 133                         cs->flags |= CLOCK_SOURCE_WATCHDOG;
 134                         cs->wd_last = csnow;
 135                 } else {
 136                         cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
 137                         cs->wd_last = csnow;
 138                         /* Check the delta. Might remove from the list ! */
 139                         clocksource_ratewd(cs, cs_nsec - wd_nsec);
 140                 }
 141         }
 142
 143         if (!list_empty(&watchdog_list)) {
 144                 /*
 145                  * Cycle through CPUs to check if the CPUs stay
 146                  * synchronized to each other.
 147                  */
 148                 int next_cpu = next_cpu_nr(raw_smp_processor_id(), cpu_online_map);
 149
 150                 if (next_cpu >= nr_cpu_ids)
 151                         next_cpu = first_cpu(cpu_online_map);
 152                 watchdog_timer.expires += WATCHDOG_INTERVAL;
 153                 add_timer_on(&watchdog_timer, next_cpu);
 154         }
 155         spin_unlock(&watchdog_lock);
 156 }
 157 static void clocksource_resume_watchdog(void)
 158 {
 159         set_bit(0, &watchdog_resumed);
 160 }
 161
 162 static void clocksource_check_watchdog(struct clocksource *cs)
 163 {
 164         struct clocksource *cse;
 165         unsigned long flags;
 166
 167         spin_lock_irqsave(&watchdog_lock, flags);
 168         if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
 169                 int started = !list_empty(&watchdog_list);
 170
 171                 list_add(&cs->wd_list, &watchdog_list);
 172                 if (!started && watchdog) {
 173                         watchdog_last = watchdog->read();
 174                         watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
 175                         add_timer_on(&watchdog_timer,
 176                                      first_cpu(cpu_online_map));
 177                 }
 178         } else {
 179                 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 180                         cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 181
 182                 if (!watchdog || cs->rating > watchdog->rating) {
 183                         if (watchdog)
 184                                 del_timer(&watchdog_timer);
 185                         watchdog = cs;
 186                         init_timer(&watchdog_timer);
 187                         watchdog_timer.function = clocksource_watchdog;
 188
 189                         /* Reset watchdog cycles */
 190                         list_for_each_entry(cse, &watchdog_list, wd_list)
 191                                 cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
 192                         /* Start if list is not empty */
 193                         if (!list_empty(&watchdog_list)) {
 194                                 watchdog_last = watchdog->read();
 195                                 watchdog_timer.expires =
 196                                         jiffies + WATCHDOG_INTERVAL;
 197                                 add_timer_on(&watchdog_timer,
 198                                              first_cpu(cpu_online_map));
 199                         }
 200                 }
 201         }
 202         spin_unlock_irqrestore(&watchdog_lock, flags);
 203 }
 204 #else
 205 static void clocksource_check_watchdog(struct clocksource *cs)
 206 {
 207         if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 208                 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 209 }
 210
 211 static inline void clocksource_resume_watchdog(void) { }
 212 #endif
 213
 214 /**
 215  * clocksource_resume - resume the clocksource(s)
 216  */
 217 void clocksource_resume(void)
 218 {
 219         struct clocksource *cs;
 220         unsigned long flags;
 221
 222         spin_lock_irqsave(&clocksource_lock, flags);
 223
 224         list_for_each_entry(cs, &clocksource_list, list) {
 225                 if (cs->resume)
 226                         cs->resume();
 227         }
 228
 229         clocksource_resume_watchdog();
 230
 231         spin_unlock_irqrestore(&clocksource_lock, flags);
 232 }
 233
 234 /**
 235  * clocksource_touch_watchdog - Update watchdog
 236  *
 237  * Update the watchdog after exception contexts such as kgdb so as not
 238  * to incorrectly trip the watchdog.
 239  *
 240  */
 241 void clocksource_touch_watchdog(void)
 242 {
 243         clocksource_resume_watchdog();
 244 }
 245
 246 /**
 247  * clocksource_get_next - Returns the selected clocksource
 248  *
 249  */
 250 struct clocksource *clocksource_get_next(void)
 251 {
 252         unsigned long flags;
 253
 254         spin_lock_irqsave(&clocksource_lock, flags);
 255         if (next_clocksource && finished_booting) {
 256                 curr_clocksource = next_clocksource;
 257                 next_clocksource = NULL;
 258         }
 259         spin_unlock_irqrestore(&clocksource_lock, flags);
 260
 261         return curr_clocksource;
 262 }
 263
 264 /**
 265  * select_clocksource - Selects the best registered clocksource.
 266  *
 267  * Private function. Must hold clocksource_lock when called.
 268  *
 269  * Select the clocksource with the best rating, or the clocksource,
 270  * which is selected by userspace override.
 271  */
 272 static struct clocksource *select_clocksource(void)
 273 {
 274         struct clocksource *next;
 275
 276         if (list_empty(&clocksource_list))
 277                 return NULL;
 278
 279         if (clocksource_override)
 280                 next = clocksource_override;
 281         else
 282                 next = list_entry(clocksource_list.next, struct clocksource,
 283                                   list);
 284
 285         if (next == curr_clocksource)
 286                 return NULL;
 287
 288         return next;
 289 }
 290
 291 /*
 292  * Enqueue the clocksource sorted by rating
 293  */
 294 static int clocksource_enqueue(struct clocksource *c)
 295 {
 296         struct list_head *tmp, *entry = &clocksource_list;
 297
 298         list_for_each(tmp, &clocksource_list) {
 299                 struct clocksource *cs;
 300
 301                 cs = list_entry(tmp, struct clocksource, list);
 302                 if (cs == c)
 303                         return -EBUSY;
 304                 /* Keep track of the place, where to insert */
 305                 if (cs->rating >= c->rating)
 306                         entry = tmp;
 307         }
 308         list_add(&c->list, entry);
 309
 310         if (strlen(c->name) == strlen(override_name) &&
 311             !strcmp(c->name, override_name))
 312                 clocksource_override = c;
 313
 314         return 0;
 315 }
 316
 317 /**
 318  * clocksource_register - Used to install new clocksources
 319  * @t:          clocksource to be registered
 320  *
 321  * Returns -EBUSY if registration fails, zero otherwise.
 322  */
 323 int clocksource_register(struct clocksource *c)
 324 {
 325         unsigned long flags;
 326         int ret;
 327
 328         spin_lock_irqsave(&clocksource_lock, flags);
 329         ret = clocksource_enqueue(c);
 330         if (!ret)
 331                 next_clocksource = select_clocksource();
 332         spin_unlock_irqrestore(&clocksource_lock, flags);
 333         if (!ret)
 334                 clocksource_check_watchdog(c);
 335         return ret;
 336 }
 337 EXPORT_SYMBOL(clocksource_register);
 338
 339 /**
 340  * clocksource_change_rating - Change the rating of a registered clocksource
 341  *
 342  */
 343 void clocksource_change_rating(struct clocksource *cs, int rating)
 344 {
 345         unsigned long flags;
 346
 347         spin_lock_irqsave(&clocksource_lock, flags);
 348         list_del(&cs->list);
 349         cs->rating = rating;
 350         clocksource_enqueue(cs);
 351         next_clocksource = select_clocksource();
 352         spin_unlock_irqrestore(&clocksource_lock, flags);
 353 }
 354
 355 /**
 356  * clocksource_unregister - remove a registered clocksource
 357  */
 358 void clocksource_unregister(struct clocksource *cs)
 359 {
 360         unsigned long flags;
 361
 362         spin_lock_irqsave(&clocksource_lock, flags);
 363         list_del(&cs->list);
 364         if (clocksource_override == cs)
 365                 clocksource_override = NULL;
 366         next_clocksource = select_clocksource();
 367         spin_unlock_irqrestore(&clocksource_lock, flags);
 368 }
 369
 370 #ifdef CONFIG_SYSFS
 371 /**
 372  * sysfs_show_current_clocksources - sysfs interface for current clocksource
 373  * @dev:        unused
 374  * @buf:        char buffer to be filled with clocksource list
 375  *
 376  * Provides sysfs interface for listing current clocksource.
 377  */
 378 static ssize_t
 379 sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
 380 {
 381         ssize_t count = 0;
 382
 383         spin_lock_irq(&clocksource_lock);
 384         count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
 385         spin_unlock_irq(&clocksource_lock);
 386
 387         return count;
 388 }
 389
 390 /**
 391  * sysfs_override_clocksource - interface for manually overriding clocksource
 392  * @dev:        unused
 393  * @buf:        name of override clocksource
 394  * @count:      length of buffer
 395  *
 396  * Takes input from sysfs interface for manually overriding the default
 397  * clocksource selction.
 398  */
 399 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
 400                                           const char *buf, size_t count)
 401 {
 402         struct clocksource *ovr = NULL;
 403         size_t ret = count;
 404         int len;
 405
 406         /* strings from sysfs write are not 0 terminated! */
 407         if (count >= sizeof(override_name))
 408                 return -EINVAL;
 409
 410         /* strip of \n: */
 411         if (buf[count-1] == '\n')
 412                 count--;
 413
 414         spin_lock_irq(&clocksource_lock);
 415
 416         if (count > 0)
 417                 memcpy(override_name, buf, count);
 418         override_name[count] = 0;
 419
 420         len = strlen(override_name);
 421         if (len) {
 422                 struct clocksource *cs;
 423
 424                 ovr = clocksource_override;
 425                 /* try to select it: */
 426                 list_for_each_entry(cs, &clocksource_list, list) {
 427                         if (strlen(cs->name) == len &&
 428                             !strcmp(cs->name, override_name))
 429                                 ovr = cs;
 430                 }
 431         }
 432
 433         /* Reselect, when the override name has changed */
 434         if (ovr != clocksource_override) {
 435                 clocksource_override = ovr;
 436                 next_clocksource = select_clocksource();
 437         }
 438
 439         spin_unlock_irq(&clocksource_lock);
 440
 441         return ret;
 442 }
 443
 444 /**
 445  * sysfs_show_available_clocksources - sysfs interface for listing clocksource
 446  * @dev:        unused
 447  * @buf:        char buffer to be filled with clocksource list
 448  *
 449  * Provides sysfs interface for listing registered clocksources
 450  */
 451 static ssize_t
 452 sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
 453 {
 454         struct clocksource *src;
 455         ssize_t count = 0;
 456
 457         spin_lock_irq(&clocksource_lock);
 458         list_for_each_entry(src, &clocksource_list, list) {
 459                 count += snprintf(buf + count,
 460                                   max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
 461                                   "%s ", src->name);
 462         }
 463         spin_unlock_irq(&clocksource_lock);
 464
 465         count += snprintf(buf + count,
 466                           max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
 467
 468         return count;
 469 }
 470
 471 /*
 472  * Sysfs setup bits:
 473  */
 474 static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
 475                    sysfs_override_clocksource);
 476
 477 static SYSDEV_ATTR(available_clocksource, 0444,
 478                    sysfs_show_available_clocksources, NULL);
 479
 480 static struct sysdev_class clocksource_sysclass = {
 481         .name = "clocksource",
 482 };
 483
 484 static struct sys_device device_clocksource = {
 485         .id     = 0,
 486         .cls    = &clocksource_sysclass,
 487 };
 488
 489 static int __init init_clocksource_sysfs(void)
 490 {
 491         int error = sysdev_class_register(&clocksource_sysclass);
 492
 493         if (!error)
 494                 error = sysdev_register(&device_clocksource);
 495         if (!error)
 496                 error = sysdev_create_file(
 497                                 &device_clocksource,
 498                                 &attr_current_clocksource);
 499         if (!error)
 500                 error = sysdev_create_file(
 501                                 &device_clocksource,
 502                                 &attr_available_clocksource);
 503         return error;
 504 }
 505
 506 device_initcall(init_clocksource_sysfs);
 507 #endif /* CONFIG_SYSFS */
 508
 509 /**
 510  * boot_override_clocksource - boot clock override
 511  * @str:        override name
 512  *
 513  * Takes a clocksource= boot argument and uses it
 514  * as the clocksource override name.
 515  */
 516 static int __init boot_override_clocksource(char* str)
 517 {
 518         unsigned long flags;
 519         spin_lock_irqsave(&clocksource_lock, flags);
 520         if (str)
 521                 strlcpy(override_name, str, sizeof(override_name));
 522         spin_unlock_irqrestore(&clocksource_lock, flags);
 523         return 1;
 524 }
 525
 526 __setup("clocksource=", boot_override_clocksource);
 527
 528 /**
 529  * boot_override_clock - Compatibility layer for deprecated boot option
 530  * @str:        override name
 531  *
 532  * DEPRECATED! Takes a clock= boot argument and uses it
 533  * as the clocksource override name
 534  */
 535 static int __init boot_override_clock(char* str)
 536 {
 537         if (!strcmp(str, "pmtmr")) {
 538                 printk("Warning: clock=pmtmr is deprecated. "
 539                         "Use clocksource=acpi_pm.\n");
 540                 return boot_override_clocksource("acpi_pm");
 541         }
 542         printk("Warning! clock= boot option is deprecated. "
 543                 "Use clocksource=xyz\n");
 544         return boot_override_clocksource(str);
 545 }
 546
 547 __setup("clock=", boot_override_clock);