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 /*
  78  * Interval: 0.5sec Treshold: 0.0625s
  79  */
  80 #define WATCHDOG_INTERVAL (HZ >> 1)
  81 #define WATCHDOG_TRESHOLD (NSEC_PER_SEC >> 4)
  82
  83 static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
  84 {
  85         if (delta > -WATCHDOG_TRESHOLD && delta < WATCHDOG_TRESHOLD)
  86                 return;
  87
  88         printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
  89                cs->name, delta);
  90         cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
  91         clocksource_change_rating(cs, 0);
  92         cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
  93         list_del(&cs->wd_list);
  94 }
  95
  96 static void clocksource_watchdog(unsigned long data)
  97 {
  98         struct clocksource *cs, *tmp;
  99         cycle_t csnow, wdnow;
 100         int64_t wd_nsec, cs_nsec;
 101
 102         spin_lock(&watchdog_lock);
 103
 104         wdnow = watchdog->read();
 105         wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
 106         watchdog_last = wdnow;
 107
 108         list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
 109                 csnow = cs->read();
 110                 /* Initialized ? */
 111                 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
 112                         if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
 113                             (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
 114                                 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 115                                 /*
 116                                  * We just marked the clocksource as
 117                                  * highres-capable, notify the rest of the
 118                                  * system as well so that we transition
 119                                  * into high-res mode:
 120                                  */
 121                                 tick_clock_notify();
 122                         }
 123                         cs->flags |= CLOCK_SOURCE_WATCHDOG;
 124                         cs->wd_last = csnow;
 125                 } else {
 126                         cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
 127                         cs->wd_last = csnow;
 128                         /* Check the delta. Might remove from the list ! */
 129                         clocksource_ratewd(cs, cs_nsec - wd_nsec);
 130                 }
 131         }
 132
 133         if (!list_empty(&watchdog_list)) {
 134                 __mod_timer(&watchdog_timer,
 135                             watchdog_timer.expires + WATCHDOG_INTERVAL);
 136         }
 137         spin_unlock(&watchdog_lock);
 138 }
 139 static void clocksource_check_watchdog(struct clocksource *cs)
 140 {
 141         struct clocksource *cse;
 142         unsigned long flags;
 143
 144         spin_lock_irqsave(&watchdog_lock, flags);
 145         if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
 146                 int started = !list_empty(&watchdog_list);
 147
 148                 list_add(&cs->wd_list, &watchdog_list);
 149                 if (!started && watchdog) {
 150                         watchdog_last = watchdog->read();
 151                         watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
 152                         add_timer(&watchdog_timer);
 153                 }
 154         } else {
 155                 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 156                         cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 157
 158                 if (!watchdog || cs->rating > watchdog->rating) {
 159                         if (watchdog)
 160                                 del_timer(&watchdog_timer);
 161                         watchdog = cs;
 162                         init_timer(&watchdog_timer);
 163                         watchdog_timer.function = clocksource_watchdog;
 164
 165                         /* Reset watchdog cycles */
 166                         list_for_each_entry(cse, &watchdog_list, wd_list)
 167                                 cse->flags &= ~CLOCK_SOURCE_WATCHDOG;
 168                         /* Start if list is not empty */
 169                         if (!list_empty(&watchdog_list)) {
 170                                 watchdog_last = watchdog->read();
 171                                 watchdog_timer.expires =
 172                                         jiffies + WATCHDOG_INTERVAL;
 173                                 add_timer(&watchdog_timer);
 174                         }
 175                 }
 176         }
 177         spin_unlock_irqrestore(&watchdog_lock, flags);
 178 }
 179 #else
 180 static void clocksource_check_watchdog(struct clocksource *cs)
 181 {
 182         if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
 183                 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
 184 }
 185 #endif
 186
 187 /**
 188  * clocksource_get_next - Returns the selected clocksource
 189  *
 190  */
 191 struct clocksource *clocksource_get_next(void)
 192 {
 193         unsigned long flags;
 194
 195         spin_lock_irqsave(&clocksource_lock, flags);
 196         if (next_clocksource && finished_booting) {
 197                 curr_clocksource = next_clocksource;
 198                 next_clocksource = NULL;
 199         }
 200         spin_unlock_irqrestore(&clocksource_lock, flags);
 201
 202         return curr_clocksource;
 203 }
 204
 205 /**
 206  * select_clocksource - Selects the best registered clocksource.
 207  *
 208  * Private function. Must hold clocksource_lock when called.
 209  *
 210  * Select the clocksource with the best rating, or the clocksource,
 211  * which is selected by userspace override.
 212  */
 213 static struct clocksource *select_clocksource(void)
 214 {
 215         struct clocksource *next;
 216
 217         if (list_empty(&clocksource_list))
 218                 return NULL;
 219
 220         if (clocksource_override)
 221                 next = clocksource_override;
 222         else
 223                 next = list_entry(clocksource_list.next, struct clocksource,
 224                                   list);
 225
 226         if (next == curr_clocksource)
 227                 return NULL;
 228
 229         return next;
 230 }
 231
 232 /*
 233  * Enqueue the clocksource sorted by rating
 234  */
 235 static int clocksource_enqueue(struct clocksource *c)
 236 {
 237         struct list_head *tmp, *entry = &clocksource_list;
 238
 239         list_for_each(tmp, &clocksource_list) {
 240                 struct clocksource *cs;
 241
 242                 cs = list_entry(tmp, struct clocksource, list);
 243                 if (cs == c)
 244                         return -EBUSY;
 245                 /* Keep track of the place, where to insert */
 246                 if (cs->rating >= c->rating)
 247                         entry = tmp;
 248         }
 249         list_add(&c->list, entry);
 250
 251         if (strlen(c->name) == strlen(override_name) &&
 252             !strcmp(c->name, override_name))
 253                 clocksource_override = c;
 254
 255         return 0;
 256 }
 257
 258 /**
 259  * clocksource_register - Used to install new clocksources
 260  * @t:          clocksource to be registered
 261  *
 262  * Returns -EBUSY if registration fails, zero otherwise.
 263  */
 264 int clocksource_register(struct clocksource *c)
 265 {
 266         unsigned long flags;
 267         int ret;
 268
 269         spin_lock_irqsave(&clocksource_lock, flags);
 270         ret = clocksource_enqueue(c);
 271         if (!ret)
 272                 next_clocksource = select_clocksource();
 273         spin_unlock_irqrestore(&clocksource_lock, flags);
 274         if (!ret)
 275                 clocksource_check_watchdog(c);
 276         return ret;
 277 }
 278 EXPORT_SYMBOL(clocksource_register);
 279
 280 /**
 281  * clocksource_change_rating - Change the rating of a registered clocksource
 282  *
 283  */
 284 void clocksource_change_rating(struct clocksource *cs, int rating)
 285 {
 286         unsigned long flags;
 287
 288         spin_lock_irqsave(&clocksource_lock, flags);
 289         list_del(&cs->list);
 290         cs->rating = rating;
 291         clocksource_enqueue(cs);
 292         next_clocksource = select_clocksource();
 293         spin_unlock_irqrestore(&clocksource_lock, flags);
 294 }
 295
 296 #ifdef CONFIG_SYSFS
 297 /**
 298  * sysfs_show_current_clocksources - sysfs interface for current clocksource
 299  * @dev:        unused
 300  * @buf:        char buffer to be filled with clocksource list
 301  *
 302  * Provides sysfs interface for listing current clocksource.
 303  */
 304 static ssize_t
 305 sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
 306 {
 307         char *curr = buf;
 308
 309         spin_lock_irq(&clocksource_lock);
 310         curr += sprintf(curr, "%s ", curr_clocksource->name);
 311         spin_unlock_irq(&clocksource_lock);
 312
 313         curr += sprintf(curr, "\n");
 314
 315         return curr - buf;
 316 }
 317
 318 /**
 319  * sysfs_override_clocksource - interface for manually overriding clocksource
 320  * @dev:        unused
 321  * @buf:        name of override clocksource
 322  * @count:      length of buffer
 323  *
 324  * Takes input from sysfs interface for manually overriding the default
 325  * clocksource selction.
 326  */
 327 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
 328                                           const char *buf, size_t count)
 329 {
 330         struct clocksource *ovr = NULL;
 331         struct list_head *tmp;
 332         size_t ret = count;
 333         int len;
 334
 335         /* strings from sysfs write are not 0 terminated! */
 336         if (count >= sizeof(override_name))
 337                 return -EINVAL;
 338
 339         /* strip of \n: */
 340         if (buf[count-1] == '\n')
 341                 count--;
 342
 343         spin_lock_irq(&clocksource_lock);
 344
 345         if (count > 0)
 346                 memcpy(override_name, buf, count);
 347         override_name[count] = 0;
 348
 349         len = strlen(override_name);
 350         if (len) {
 351                 ovr = clocksource_override;
 352                 /* try to select it: */
 353                 list_for_each(tmp, &clocksource_list) {
 354                         struct clocksource *cs;
 355
 356                         cs = list_entry(tmp, struct clocksource, list);
 357                         if (strlen(cs->name) == len &&
 358                             !strcmp(cs->name, override_name))
 359                                 ovr = cs;
 360                 }
 361         }
 362
 363         /* Reselect, when the override name has changed */
 364         if (ovr != clocksource_override) {
 365                 clocksource_override = ovr;
 366                 next_clocksource = select_clocksource();
 367         }
 368
 369         spin_unlock_irq(&clocksource_lock);
 370
 371         return ret;
 372 }
 373
 374 /**
 375  * sysfs_show_available_clocksources - sysfs interface for listing clocksource
 376  * @dev:        unused
 377  * @buf:        char buffer to be filled with clocksource list
 378  *
 379  * Provides sysfs interface for listing registered clocksources
 380  */
 381 static ssize_t
 382 sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
 383 {
 384         struct list_head *tmp;
 385         char *curr = buf;
 386
 387         spin_lock_irq(&clocksource_lock);
 388         list_for_each(tmp, &clocksource_list) {
 389                 struct clocksource *src;
 390
 391                 src = list_entry(tmp, struct clocksource, list);
 392                 curr += sprintf(curr, "%s ", src->name);
 393         }
 394         spin_unlock_irq(&clocksource_lock);
 395
 396         curr += sprintf(curr, "\n");
 397
 398         return curr - buf;
 399 }
 400
 401 /*
 402  * Sysfs setup bits:
 403  */
 404 static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
 405                    sysfs_override_clocksource);
 406
 407 static SYSDEV_ATTR(available_clocksource, 0600,
 408                    sysfs_show_available_clocksources, NULL);
 409
 410 static struct sysdev_class clocksource_sysclass = {
 411         set_kset_name("clocksource"),
 412 };
 413
 414 static struct sys_device device_clocksource = {
 415         .id     = 0,
 416         .cls    = &clocksource_sysclass,
 417 };
 418
 419 static int __init init_clocksource_sysfs(void)
 420 {
 421         int error = sysdev_class_register(&clocksource_sysclass);
 422
 423         if (!error)
 424                 error = sysdev_register(&device_clocksource);
 425         if (!error)
 426                 error = sysdev_create_file(
 427                                 &device_clocksource,
 428                                 &attr_current_clocksource);
 429         if (!error)
 430                 error = sysdev_create_file(
 431                                 &device_clocksource,
 432                                 &attr_available_clocksource);
 433         return error;
 434 }
 435
 436 device_initcall(init_clocksource_sysfs);
 437 #endif /* CONFIG_SYSFS */
 438
 439 /**
 440  * boot_override_clocksource - boot clock override
 441  * @str:        override name
 442  *
 443  * Takes a clocksource= boot argument and uses it
 444  * as the clocksource override name.
 445  */
 446 static int __init boot_override_clocksource(char* str)
 447 {
 448         unsigned long flags;
 449         spin_lock_irqsave(&clocksource_lock, flags);
 450         if (str)
 451                 strlcpy(override_name, str, sizeof(override_name));
 452         spin_unlock_irqrestore(&clocksource_lock, flags);
 453         return 1;
 454 }
 455
 456 __setup("clocksource=", boot_override_clocksource);
 457
 458 /**
 459  * boot_override_clock - Compatibility layer for deprecated boot option
 460  * @str:        override name
 461  *
 462  * DEPRECATED! Takes a clock= boot argument and uses it
 463  * as the clocksource override name
 464  */
 465 static int __init boot_override_clock(char* str)
 466 {
 467         if (!strcmp(str, "pmtmr")) {
 468                 printk("Warning: clock=pmtmr is deprecated. "
 469                         "Use clocksource=acpi_pm.\n");
 470                 return boot_override_clocksource("acpi_pm");
 471         }
 472         printk("Warning! clock= boot option is deprecated. "
 473                 "Use clocksource=xyz\n");
 474         return boot_override_clocksource(str);
 475 }
 476
 477 __setup("clock=", boot_override_clock);