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                 __mod_timer(&watchdog_timer,
 145                             watchdog_timer.expires + WATCHDOG_INTERVAL);
 146         }
 147         spin_unlock(&watchdog_lock);
 148 }
 149 static void clocksource_resume_watchdog(void)
 150 {
 151         set_bit(0, &watchdog_resumed);
 152 }
 153
 154 static void clocksource_check_watchdog(struct clocksource *cs)
 155 {
 156         struct clocksource *cse;
 157         unsigned long flags;
 158
 159         spin_lock_irqsave(&watchdog_lock, flags);
 160         if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
 161                 int started = !list_empty(&watchdog_list);
 162
 163                 list_add(&cs->wd_list, &watchdog_list);
 164                 if (!started && watchdog) {
 165                         watchdog_last = watchdog->read();
 166                         watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
 167                         add_timer(&watchdog_timer);
 168                 }
 169         } else {
 170                 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 171                         cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 172
 173                 if (!watchdog || cs->rating > watchdog->rating) {
 174                         if (watchdog)
 175                                 del_timer(&watchdog_timer);
 176                         watchdog = cs;
 177                         init_timer_deferrable(&watchdog_timer);
 178                         watchdog_timer.function = clocksource_watchdog;
 179
 180                         /* Reset watchdog cycles */
 181                         list_for_each_entry(cse, &watchdog_list, wd_list)
 182                                 cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
 183                         /* Start if list is not empty */
 184                         if (!list_empty(&watchdog_list)) {
 185                                 watchdog_last = watchdog->read();
 186                                 watchdog_timer.expires =
 187                                         jiffies + WATCHDOG_INTERVAL;
 188                                 add_timer(&watchdog_timer);
 189                         }
 190                 }
 191         }
 192         spin_unlock_irqrestore(&watchdog_lock, flags);
 193 }
 194 #else
 195 static void clocksource_check_watchdog(struct clocksource *cs)
 196 {
 197         if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 198                 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 199 }
 200
 201 static inline void clocksource_resume_watchdog(void) { }
 202 #endif
 203
 204 /**
 205  * clocksource_resume - resume the clocksource(s)
 206  */
 207 void clocksource_resume(void)
 208 {
 209         struct clocksource *cs;
 210         unsigned long flags;
 211
 212         spin_lock_irqsave(&clocksource_lock, flags);
 213
 214         list_for_each_entry(cs, &clocksource_list, list) {
 215                 if (cs->resume)
 216                         cs->resume();
 217         }
 218
 219         clocksource_resume_watchdog();
 220
 221         spin_unlock_irqrestore(&clocksource_lock, flags);
 222 }
 223
 224 /**
 225  * clocksource_get_next - Returns the selected clocksource
 226  *
 227  */
 228 struct clocksource *clocksource_get_next(void)
 229 {
 230         unsigned long flags;
 231
 232         spin_lock_irqsave(&clocksource_lock, flags);
 233         if (next_clocksource && finished_booting) {
 234                 curr_clocksource = next_clocksource;
 235                 next_clocksource = NULL;
 236         }
 237         spin_unlock_irqrestore(&clocksource_lock, flags);
 238
 239         return curr_clocksource;
 240 }
 241
 242 /**
 243  * select_clocksource - Selects the best registered clocksource.
 244  *
 245  * Private function. Must hold clocksource_lock when called.
 246  *
 247  * Select the clocksource with the best rating, or the clocksource,
 248  * which is selected by userspace override.
 249  */
 250 static struct clocksource *select_clocksource(void)
 251 {
 252         struct clocksource *next;
 253
 254         if (list_empty(&clocksource_list))
 255                 return NULL;
 256
 257         if (clocksource_override)
 258                 next = clocksource_override;
 259         else
 260                 next = list_entry(clocksource_list.next, struct clocksource,
 261                                   list);
 262
 263         if (next == curr_clocksource)
 264                 return NULL;
 265
 266         return next;
 267 }
 268
 269 /*
 270  * Enqueue the clocksource sorted by rating
 271  */
 272 static int clocksource_enqueue(struct clocksource *c)
 273 {
 274         struct list_head *tmp, *entry = &clocksource_list;
 275
 276         list_for_each(tmp, &clocksource_list) {
 277                 struct clocksource *cs;
 278
 279                 cs = list_entry(tmp, struct clocksource, list);
 280                 if (cs == c)
 281                         return -EBUSY;
 282                 /* Keep track of the place, where to insert */
 283                 if (cs->rating >= c->rating)
 284                         entry = tmp;
 285         }
 286         list_add(&c->list, entry);
 287
 288         if (strlen(c->name) == strlen(override_name) &&
 289             !strcmp(c->name, override_name))
 290                 clocksource_override = c;
 291
 292         return 0;
 293 }
 294
 295 /**
 296  * clocksource_register - Used to install new clocksources
 297  * @t:          clocksource to be registered
 298  *
 299  * Returns -EBUSY if registration fails, zero otherwise.
 300  */
 301 int clocksource_register(struct clocksource *c)
 302 {
 303         unsigned long flags;
 304         int ret;
 305
 306         spin_lock_irqsave(&clocksource_lock, flags);
 307         ret = clocksource_enqueue(c);
 308         if (!ret)
 309                 next_clocksource = select_clocksource();
 310         spin_unlock_irqrestore(&clocksource_lock, flags);
 311         if (!ret)
 312                 clocksource_check_watchdog(c);
 313         return ret;
 314 }
 315 EXPORT_SYMBOL(clocksource_register);
 316
 317 /**
 318  * clocksource_change_rating - Change the rating of a registered clocksource
 319  *
 320  */
 321 void clocksource_change_rating(struct clocksource *cs, int rating)
 322 {
 323         unsigned long flags;
 324
 325         spin_lock_irqsave(&clocksource_lock, flags);
 326         list_del(&cs->list);
 327         cs->rating = rating;
 328         clocksource_enqueue(cs);
 329         next_clocksource = select_clocksource();
 330         spin_unlock_irqrestore(&clocksource_lock, flags);
 331 }
 332
 333 /**
 334  * clocksource_unregister - remove a registered clocksource
 335  */
 336 void clocksource_unregister(struct clocksource *cs)
 337 {
 338         unsigned long flags;
 339
 340         spin_lock_irqsave(&clocksource_lock, flags);
 341         list_del(&cs->list);
 342         if (clocksource_override == cs)
 343                 clocksource_override = NULL;
 344         next_clocksource = select_clocksource();
 345         spin_unlock_irqrestore(&clocksource_lock, flags);
 346 }
 347
 348 #ifdef CONFIG_SYSFS
 349 /**
 350  * sysfs_show_current_clocksources - sysfs interface for current clocksource
 351  * @dev:        unused
 352  * @buf:        char buffer to be filled with clocksource list
 353  *
 354  * Provides sysfs interface for listing current clocksource.
 355  */
 356 static ssize_t
 357 sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
 358 {
 359         ssize_t count = 0;
 360
 361         spin_lock_irq(&clocksource_lock);
 362         count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
 363         spin_unlock_irq(&clocksource_lock);
 364
 365         return count;
 366 }
 367
 368 /**
 369  * sysfs_override_clocksource - interface for manually overriding clocksource
 370  * @dev:        unused
 371  * @buf:        name of override clocksource
 372  * @count:      length of buffer
 373  *
 374  * Takes input from sysfs interface for manually overriding the default
 375  * clocksource selction.
 376  */
 377 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
 378                                           const char *buf, size_t count)
 379 {
 380         struct clocksource *ovr = NULL;
 381         size_t ret = count;
 382         int len;
 383
 384         /* strings from sysfs write are not 0 terminated! */
 385         if (count >= sizeof(override_name))
 386                 return -EINVAL;
 387
 388         /* strip of \n: */
 389         if (buf[count-1] == '\n')
 390                 count--;
 391
 392         spin_lock_irq(&clocksource_lock);
 393
 394         if (count > 0)
 395                 memcpy(override_name, buf, count);
 396         override_name[count] = 0;
 397
 398         len = strlen(override_name);
 399         if (len) {
 400                 struct clocksource *cs;
 401
 402                 ovr = clocksource_override;
 403                 /* try to select it: */
 404                 list_for_each_entry(cs, &clocksource_list, list) {
 405                         if (strlen(cs->name) == len &&
 406                             !strcmp(cs->name, override_name))
 407                                 ovr = cs;
 408                 }
 409         }
 410
 411         /* Reselect, when the override name has changed */
 412         if (ovr != clocksource_override) {
 413                 clocksource_override = ovr;
 414                 next_clocksource = select_clocksource();
 415         }
 416
 417         spin_unlock_irq(&clocksource_lock);
 418
 419         return ret;
 420 }
 421
 422 /**
 423  * sysfs_show_available_clocksources - sysfs interface for listing clocksource
 424  * @dev:        unused
 425  * @buf:        char buffer to be filled with clocksource list
 426  *
 427  * Provides sysfs interface for listing registered clocksources
 428  */
 429 static ssize_t
 430 sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
 431 {
 432         struct clocksource *src;
 433         ssize_t count = 0;
 434
 435         spin_lock_irq(&clocksource_lock);
 436         list_for_each_entry(src, &clocksource_list, list) {
 437                 count += snprintf(buf + count,
 438                                   max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
 439                                   "%s ", src->name);
 440         }
 441         spin_unlock_irq(&clocksource_lock);
 442
 443         count += snprintf(buf + count,
 444                           max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
 445
 446         return count;
 447 }
 448
 449 /*
 450  * Sysfs setup bits:
 451  */
 452 static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
 453                    sysfs_override_clocksource);
 454
 455 static SYSDEV_ATTR(available_clocksource, 0600,
 456                    sysfs_show_available_clocksources, NULL);
 457
 458 static struct sysdev_class clocksource_sysclass = {
 459         .name = "clocksource",
 460 };
 461
 462 static struct sys_device device_clocksource = {
 463         .id     = 0,
 464         .cls    = &clocksource_sysclass,
 465 };
 466
 467 static int __init init_clocksource_sysfs(void)
 468 {
 469         int error = sysdev_class_register(&clocksource_sysclass);
 470
 471         if (!error)
 472                 error = sysdev_register(&device_clocksource);
 473         if (!error)
 474                 error = sysdev_create_file(
 475                                 &device_clocksource,
 476                                 &attr_current_clocksource);
 477         if (!error)
 478                 error = sysdev_create_file(
 479                                 &device_clocksource,
 480                                 &attr_available_clocksource);
 481         return error;
 482 }
 483
 484 device_initcall(init_clocksource_sysfs);
 485 #endif /* CONFIG_SYSFS */
 486
 487 /**
 488  * boot_override_clocksource - boot clock override
 489  * @str:        override name
 490  *
 491  * Takes a clocksource= boot argument and uses it
 492  * as the clocksource override name.
 493  */
 494 static int __init boot_override_clocksource(char* str)
 495 {
 496         unsigned long flags;
 497         spin_lock_irqsave(&clocksource_lock, flags);
 498         if (str)
 499                 strlcpy(override_name, str, sizeof(override_name));
 500         spin_unlock_irqrestore(&clocksource_lock, flags);
 501         return 1;
 502 }
 503
 504 __setup("clocksource=", boot_override_clocksource);
 505
 506 /**
 507  * boot_override_clock - Compatibility layer for deprecated boot option
 508  * @str:        override name
 509  *
 510  * DEPRECATED! Takes a clock= boot argument and uses it
 511  * as the clocksource override name
 512  */
 513 static int __init boot_override_clock(char* str)
 514 {
 515         if (!strcmp(str, "pmtmr")) {
 516                 printk("Warning: clock=pmtmr is deprecated. "
 517                         "Use clocksource=acpi_pm.\n");
 518                 return boot_override_clocksource("acpi_pm");
 519         }
 520         printk("Warning! clock= boot option is deprecated. "
 521                 "Use clocksource=xyz\n");
 522         return boot_override_clocksource(str);
 523 }
 524
 525 __setup("clock=", boot_override_clock);