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