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