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 int watchdog_resumed;
  78
  79 /*
  80  * Interval: 0.5sec Treshold: 0.0625s
  81  */
  82 #define WATCHDOG_INTERVAL (HZ >> 1)
  83 #define WATCHDOG_TRESHOLD (NSEC_PER_SEC >> 4)
  84
  85 static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
  86 {
  87         if (delta > -WATCHDOG_TRESHOLD && delta < WATCHDOG_TRESHOLD)
  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         cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
  95         list_del(&cs->wd_list);
  96 }
  97
  98 static void clocksource_watchdog(unsigned long data)
  99 {
 100         struct clocksource *cs, *tmp;
 101         cycle_t csnow, wdnow;
 102         int64_t wd_nsec, cs_nsec;
 103         int resumed;
 104
 105         spin_lock(&watchdog_lock);
 106
 107         resumed = watchdog_resumed;
 108         if (unlikely(resumed))
 109                 watchdog_resumed = 0;
 110
 111         wdnow = watchdog->read();
 112         wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
 113         watchdog_last = wdnow;
 114
 115         list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
 116                 csnow = cs->read();
 117
 118                 if (unlikely(resumed)) {
 119                         cs->wd_last = csnow;
 120                         continue;
 121                 }
 122
 123                 /* Initialized ? */
 124                 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
 125                         if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
 126                             (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
 127                                 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 128                                 /*
 129                                  * We just marked the clocksource as
 130                                  * highres-capable, notify the rest of the
 131                                  * system as well so that we transition
 132                                  * into high-res mode:
 133                                  */
 134                                 tick_clock_notify();
 135                         }
 136                         cs->flags |= CLOCK_SOURCE_WATCHDOG;
 137                         cs->wd_last = csnow;
 138                 } else {
 139                         cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
 140                         cs->wd_last = csnow;
 141                         /* Check the delta. Might remove from the list ! */
 142                         clocksource_ratewd(cs, cs_nsec - wd_nsec);
 143                 }
 144         }
 145
 146         if (!list_empty(&watchdog_list)) {
 147                 __mod_timer(&watchdog_timer,
 148                             watchdog_timer.expires + WATCHDOG_INTERVAL);
 149         }
 150         spin_unlock(&watchdog_lock);
 151 }
 152 static void clocksource_resume_watchdog(void)
 153 {
 154         spin_lock(&watchdog_lock);
 155         watchdog_resumed = 1;
 156         spin_unlock(&watchdog_lock);
 157 }
 158
 159 static void clocksource_check_watchdog(struct clocksource *cs)
 160 {
 161         struct clocksource *cse;
 162         unsigned long flags;
 163
 164         spin_lock_irqsave(&watchdog_lock, flags);
 165         if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
 166                 int started = !list_empty(&watchdog_list);
 167
 168                 list_add(&cs->wd_list, &watchdog_list);
 169                 if (!started && watchdog) {
 170                         watchdog_last = watchdog->read();
 171                         watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
 172                         add_timer(&watchdog_timer);
 173                 }
 174         } else {
 175                 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 176                         cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 177
 178                 if (!watchdog || cs->rating > watchdog->rating) {
 179                         if (watchdog)
 180                                 del_timer(&watchdog_timer);
 181                         watchdog = cs;
 182                         init_timer(&watchdog_timer);
 183                         watchdog_timer.function = clocksource_watchdog;
 184
 185                         /* Reset watchdog cycles */
 186                         list_for_each_entry(cse, &watchdog_list, wd_list)
 187                                 cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
 188                         /* Start if list is not empty */
 189                         if (!list_empty(&watchdog_list)) {
 190                                 watchdog_last = watchdog->read();
 191                                 watchdog_timer.expires =
 192                                         jiffies + WATCHDOG_INTERVAL;
 193                                 add_timer(&watchdog_timer);
 194                         }
 195                 }
 196         }
 197         spin_unlock_irqrestore(&watchdog_lock, flags);
 198 }
 199 #else
 200 static void clocksource_check_watchdog(struct clocksource *cs)
 201 {
 202         if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 203                 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 204 }
 205
 206 static inline void clocksource_resume_watchdog(void) { }
 207 #endif
 208
 209 /**
 210  * clocksource_resume - resume the clocksource(s)
 211  */
 212 void clocksource_resume(void)
 213 {
 214         struct list_head *tmp;
 215         unsigned long flags;
 216
 217         spin_lock_irqsave(&clocksource_lock, flags);
 218
 219         list_for_each(tmp, &clocksource_list) {
 220                 struct clocksource *cs;
 221
 222                 cs = list_entry(tmp, struct clocksource, list);
 223                 if (cs->resume)
 224                         cs->resume();
 225         }
 226
 227         clocksource_resume_watchdog();
 228
 229         spin_unlock_irqrestore(&clocksource_lock, flags);
 230 }
 231
 232 /**
 233  * clocksource_get_next - Returns the selected clocksource
 234  *
 235  */
 236 struct clocksource *clocksource_get_next(void)
 237 {
 238         unsigned long flags;
 239
 240         spin_lock_irqsave(&clocksource_lock, flags);
 241         if (next_clocksource && finished_booting) {
 242                 curr_clocksource = next_clocksource;
 243                 next_clocksource = NULL;
 244         }
 245         spin_unlock_irqrestore(&clocksource_lock, flags);
 246
 247         return curr_clocksource;
 248 }
 249
 250 /**
 251  * select_clocksource - Selects the best registered clocksource.
 252  *
 253  * Private function. Must hold clocksource_lock when called.
 254  *
 255  * Select the clocksource with the best rating, or the clocksource,
 256  * which is selected by userspace override.
 257  */
 258 static struct clocksource *select_clocksource(void)
 259 {
 260         struct clocksource *next;
 261
 262         if (list_empty(&clocksource_list))
 263                 return NULL;
 264
 265         if (clocksource_override)
 266                 next = clocksource_override;
 267         else
 268                 next = list_entry(clocksource_list.next, struct clocksource,
 269                                   list);
 270
 271         if (next == curr_clocksource)
 272                 return NULL;
 273
 274         return next;
 275 }
 276
 277 /*
 278  * Enqueue the clocksource sorted by rating
 279  */
 280 static int clocksource_enqueue(struct clocksource *c)
 281 {
 282         struct list_head *tmp, *entry = &clocksource_list;
 283
 284         list_for_each(tmp, &clocksource_list) {
 285                 struct clocksource *cs;
 286
 287                 cs = list_entry(tmp, struct clocksource, list);
 288                 if (cs == c)
 289                         return -EBUSY;
 290                 /* Keep track of the place, where to insert */
 291                 if (cs->rating >= c->rating)
 292                         entry = tmp;
 293         }
 294         list_add(&c->list, entry);
 295
 296         if (strlen(c->name) == strlen(override_name) &&
 297             !strcmp(c->name, override_name))
 298                 clocksource_override = c;
 299
 300         return 0;
 301 }
 302
 303 /**
 304  * clocksource_register - Used to install new clocksources
 305  * @t:          clocksource to be registered
 306  *
 307  * Returns -EBUSY if registration fails, zero otherwise.
 308  */
 309 int clocksource_register(struct clocksource *c)
 310 {
 311         unsigned long flags;
 312         int ret;
 313
 314         spin_lock_irqsave(&clocksource_lock, flags);
 315         ret = clocksource_enqueue(c);
 316         if (!ret)
 317                 next_clocksource = select_clocksource();
 318         spin_unlock_irqrestore(&clocksource_lock, flags);
 319         if (!ret)
 320                 clocksource_check_watchdog(c);
 321         return ret;
 322 }
 323 EXPORT_SYMBOL(clocksource_register);
 324
 325 /**
 326  * clocksource_change_rating - Change the rating of a registered clocksource
 327  *
 328  */
 329 void clocksource_change_rating(struct clocksource *cs, int rating)
 330 {
 331         unsigned long flags;
 332
 333         spin_lock_irqsave(&clocksource_lock, flags);
 334         list_del(&cs->list);
 335         cs->rating = rating;
 336         clocksource_enqueue(cs);
 337         next_clocksource = select_clocksource();
 338         spin_unlock_irqrestore(&clocksource_lock, flags);
 339 }
 340
 341 #ifdef CONFIG_SYSFS
 342 /**
 343  * sysfs_show_current_clocksources - sysfs interface for current clocksource
 344  * @dev:        unused
 345  * @buf:        char buffer to be filled with clocksource list
 346  *
 347  * Provides sysfs interface for listing current clocksource.
 348  */
 349 static ssize_t
 350 sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
 351 {
 352         char *curr = buf;
 353
 354         spin_lock_irq(&clocksource_lock);
 355         curr += sprintf(curr, "%s ", curr_clocksource->name);
 356         spin_unlock_irq(&clocksource_lock);
 357
 358         curr += sprintf(curr, "\n");
 359
 360         return curr - buf;
 361 }
 362
 363 /**
 364  * sysfs_override_clocksource - interface for manually overriding clocksource
 365  * @dev:        unused
 366  * @buf:        name of override clocksource
 367  * @count:      length of buffer
 368  *
 369  * Takes input from sysfs interface for manually overriding the default
 370  * clocksource selction.
 371  */
 372 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
 373                                           const char *buf, size_t count)
 374 {
 375         struct clocksource *ovr = NULL;
 376         struct list_head *tmp;
 377         size_t ret = count;
 378         int len;
 379
 380         /* strings from sysfs write are not 0 terminated! */
 381         if (count >= sizeof(override_name))
 382                 return -EINVAL;
 383
 384         /* strip of \n: */
 385         if (buf[count-1] == '\n')
 386                 count--;
 387
 388         spin_lock_irq(&clocksource_lock);
 389
 390         if (count > 0)
 391                 memcpy(override_name, buf, count);
 392         override_name[count] = 0;
 393
 394         len = strlen(override_name);
 395         if (len) {
 396                 ovr = clocksource_override;
 397                 /* try to select it: */
 398                 list_for_each(tmp, &clocksource_list) {
 399                         struct clocksource *cs;
 400
 401                         cs = list_entry(tmp, struct clocksource, list);
 402                         if (strlen(cs->name) == len &&
 403                             !strcmp(cs->name, override_name))
 404                                 ovr = cs;
 405                 }
 406         }
 407
 408         /* Reselect, when the override name has changed */
 409         if (ovr != clocksource_override) {
 410                 clocksource_override = ovr;
 411                 next_clocksource = select_clocksource();
 412         }
 413
 414         spin_unlock_irq(&clocksource_lock);
 415
 416         return ret;
 417 }
 418
 419 /**
 420  * sysfs_show_available_clocksources - sysfs interface for listing clocksource
 421  * @dev:        unused
 422  * @buf:        char buffer to be filled with clocksource list
 423  *
 424  * Provides sysfs interface for listing registered clocksources
 425  */
 426 static ssize_t
 427 sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
 428 {
 429         struct list_head *tmp;
 430         char *curr = buf;
 431
 432         spin_lock_irq(&clocksource_lock);
 433         list_for_each(tmp, &clocksource_list) {
 434                 struct clocksource *src;
 435
 436                 src = list_entry(tmp, struct clocksource, list);
 437                 curr += sprintf(curr, "%s ", src->name);
 438         }
 439         spin_unlock_irq(&clocksource_lock);
 440
 441         curr += sprintf(curr, "\n");
 442
 443         return curr - buf;
 444 }
 445
 446 /*
 447  * Sysfs setup bits:
 448  */
 449 static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
 450                    sysfs_override_clocksource);
 451
 452 static SYSDEV_ATTR(available_clocksource, 0600,
 453                    sysfs_show_available_clocksources, NULL);
 454
 455 static struct sysdev_class clocksource_sysclass = {
 456         set_kset_name("clocksource"),
 457 };
 458
 459 static struct sys_device device_clocksource = {
 460         .id     = 0,
 461         .cls    = &clocksource_sysclass,
 462 };
 463
 464 static int __init init_clocksource_sysfs(void)
 465 {
 466         int error = sysdev_class_register(&clocksource_sysclass);
 467
 468         if (!error)
 469                 error = sysdev_register(&device_clocksource);
 470         if (!error)
 471                 error = sysdev_create_file(
 472                                 &device_clocksource,
 473                                 &attr_current_clocksource);
 474         if (!error)
 475                 error = sysdev_create_file(
 476                                 &device_clocksource,
 477                                 &attr_available_clocksource);
 478         return error;
 479 }
 480
 481 device_initcall(init_clocksource_sysfs);
 482 #endif /* CONFIG_SYSFS */
 483
 484 /**
 485  * boot_override_clocksource - boot clock override
 486  * @str:        override name
 487  *
 488  * Takes a clocksource= boot argument and uses it
 489  * as the clocksource override name.
 490  */
 491 static int __init boot_override_clocksource(char* str)
 492 {
 493         unsigned long flags;
 494         spin_lock_irqsave(&clocksource_lock, flags);
 495         if (str)
 496                 strlcpy(override_name, str, sizeof(override_name));
 497         spin_unlock_irqrestore(&clocksource_lock, flags);
 498         return 1;
 499 }
 500
 501 __setup("clocksource=", boot_override_clocksource);
 502
 503 /**
 504  * boot_override_clock - Compatibility layer for deprecated boot option
 505  * @str:        override name
 506  *
 507  * DEPRECATED! Takes a clock= boot argument and uses it
 508  * as the clocksource override name
 509  */
 510 static int __init boot_override_clock(char* str)
 511 {
 512         if (!strcmp(str, "pmtmr")) {
 513                 printk("Warning: clock=pmtmr is deprecated. "
 514                         "Use clocksource=acpi_pm.\n");
 515                 return boot_override_clocksource("acpi_pm");
 516         }
 517         printk("Warning! clock= boot option is deprecated. "
 518                 "Use clocksource=xyz\n");
 519         return boot_override_clocksource(str);
 520 }
 521
 522 __setup("clock=", boot_override_clock);