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