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 list_del(&cs->wd_list); 95 } 96 97 static void clocksource_watchdog(unsigned long data) 98 { 99 struct clocksource *cs, *tmp; 100 cycle_t csnow, wdnow; 101 int64_t wd_nsec, cs_nsec; 102 int resumed; 103 104 spin_lock(&watchdog_lock); 105 106 resumed = test_and_clear_bit(0, &watchdog_resumed); 107 108 wdnow = watchdog->read(); 109 wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask); 110 watchdog_last = wdnow; 111 112 list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) { 113 csnow = cs->read(); 114 115 if (unlikely(resumed)) { 116 cs->wd_last = csnow; 117 continue; 118 } 119 120 /* Initialized ? */ 121 if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) { 122 if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) && 123 (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) { 124 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 125 /* 126 * We just marked the clocksource as 127 * highres-capable, notify the rest of the 128 * system as well so that we transition 129 * into high-res mode: 130 */ 131 tick_clock_notify(); 132 } 133 cs->flags |= CLOCK_SOURCE_WATCHDOG; 134 cs->wd_last = csnow; 135 } else { 136 cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask); 137 cs->wd_last = csnow; 138 /* Check the delta. Might remove from the list ! */ 139 clocksource_ratewd(cs, cs_nsec - wd_nsec); 140 } 141 } 142 143 if (!list_empty(&watchdog_list)) { 144 /* 145 * Cycle through CPUs to check if the CPUs stay 146 * synchronized to each other. 147 */ 148 int next_cpu = next_cpu_nr(raw_smp_processor_id(), cpu_online_map); 149 150 if (next_cpu >= nr_cpu_ids) 151 next_cpu = first_cpu(cpu_online_map); 152 watchdog_timer.expires += WATCHDOG_INTERVAL; 153 add_timer_on(&watchdog_timer, next_cpu); 154 } 155 spin_unlock(&watchdog_lock); 156 } 157 static void clocksource_resume_watchdog(void) 158 { 159 set_bit(0, &watchdog_resumed); 160 } 161 162 static void clocksource_check_watchdog(struct clocksource *cs) 163 { 164 struct clocksource *cse; 165 unsigned long flags; 166 167 spin_lock_irqsave(&watchdog_lock, flags); 168 if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) { 169 int started = !list_empty(&watchdog_list); 170 171 list_add(&cs->wd_list, &watchdog_list); 172 if (!started && watchdog) { 173 watchdog_last = watchdog->read(); 174 watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL; 175 add_timer_on(&watchdog_timer, 176 first_cpu(cpu_online_map)); 177 } 178 } else { 179 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 180 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 181 182 if (!watchdog || cs->rating > watchdog->rating) { 183 if (watchdog) 184 del_timer(&watchdog_timer); 185 watchdog = cs; 186 init_timer(&watchdog_timer); 187 watchdog_timer.function = clocksource_watchdog; 188 189 /* Reset watchdog cycles */ 190 list_for_each_entry(cse, &watchdog_list, wd_list) 191 cse->flags &= ~CLOCK_SOURCE_WATCHDOG; 192 /* Start if list is not empty */ 193 if (!list_empty(&watchdog_list)) { 194 watchdog_last = watchdog->read(); 195 watchdog_timer.expires = 196 jiffies + WATCHDOG_INTERVAL; 197 add_timer_on(&watchdog_timer, 198 first_cpu(cpu_online_map)); 199 } 200 } 201 } 202 spin_unlock_irqrestore(&watchdog_lock, flags); 203 } 204 #else 205 static void clocksource_check_watchdog(struct clocksource *cs) 206 { 207 if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) 208 cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES; 209 } 210 211 static inline void clocksource_resume_watchdog(void) { } 212 #endif 213 214 /** 215 * clocksource_resume - resume the clocksource(s) 216 */ 217 void clocksource_resume(void) 218 { 219 struct clocksource *cs; 220 unsigned long flags; 221 222 spin_lock_irqsave(&clocksource_lock, flags); 223 224 list_for_each_entry(cs, &clocksource_list, list) { 225 if (cs->resume) 226 cs->resume(); 227 } 228 229 clocksource_resume_watchdog(); 230 231 spin_unlock_irqrestore(&clocksource_lock, flags); 232 } 233 234 /** 235 * clocksource_touch_watchdog - Update watchdog 236 * 237 * Update the watchdog after exception contexts such as kgdb so as not 238 * to incorrectly trip the watchdog. 239 * 240 */ 241 void clocksource_touch_watchdog(void) 242 { 243 clocksource_resume_watchdog(); 244 } 245 246 /** 247 * clocksource_get_next - Returns the selected clocksource 248 * 249 */ 250 struct clocksource *clocksource_get_next(void) 251 { 252 unsigned long flags; 253 254 spin_lock_irqsave(&clocksource_lock, flags); 255 if (next_clocksource && finished_booting) { 256 curr_clocksource = next_clocksource; 257 next_clocksource = NULL; 258 } 259 spin_unlock_irqrestore(&clocksource_lock, flags); 260 261 return curr_clocksource; 262 } 263 264 /** 265 * select_clocksource - Selects the best registered clocksource. 266 * 267 * Private function. Must hold clocksource_lock when called. 268 * 269 * Select the clocksource with the best rating, or the clocksource, 270 * which is selected by userspace override. 271 */ 272 static struct clocksource *select_clocksource(void) 273 { 274 struct clocksource *next; 275 276 if (list_empty(&clocksource_list)) 277 return NULL; 278 279 if (clocksource_override) 280 next = clocksource_override; 281 else 282 next = list_entry(clocksource_list.next, struct clocksource, 283 list); 284 285 if (next == curr_clocksource) 286 return NULL; 287 288 return next; 289 } 290 291 /* 292 * Enqueue the clocksource sorted by rating 293 */ 294 static int clocksource_enqueue(struct clocksource *c) 295 { 296 struct list_head *tmp, *entry = &clocksource_list; 297 298 list_for_each(tmp, &clocksource_list) { 299 struct clocksource *cs; 300 301 cs = list_entry(tmp, struct clocksource, list); 302 if (cs == c) 303 return -EBUSY; 304 /* Keep track of the place, where to insert */ 305 if (cs->rating >= c->rating) 306 entry = tmp; 307 } 308 list_add(&c->list, entry); 309 310 if (strlen(c->name) == strlen(override_name) && 311 !strcmp(c->name, override_name)) 312 clocksource_override = c; 313 314 return 0; 315 } 316 317 /** 318 * clocksource_register - Used to install new clocksources 319 * @t: clocksource to be registered 320 * 321 * Returns -EBUSY if registration fails, zero otherwise. 322 */ 323 int clocksource_register(struct clocksource *c) 324 { 325 unsigned long flags; 326 int ret; 327 328 spin_lock_irqsave(&clocksource_lock, flags); 329 ret = clocksource_enqueue(c); 330 if (!ret) 331 next_clocksource = select_clocksource(); 332 spin_unlock_irqrestore(&clocksource_lock, flags); 333 if (!ret) 334 clocksource_check_watchdog(c); 335 return ret; 336 } 337 EXPORT_SYMBOL(clocksource_register); 338 339 /** 340 * clocksource_change_rating - Change the rating of a registered clocksource 341 * 342 */ 343 void clocksource_change_rating(struct clocksource *cs, int rating) 344 { 345 unsigned long flags; 346 347 spin_lock_irqsave(&clocksource_lock, flags); 348 list_del(&cs->list); 349 cs->rating = rating; 350 clocksource_enqueue(cs); 351 next_clocksource = select_clocksource(); 352 spin_unlock_irqrestore(&clocksource_lock, flags); 353 } 354 355 /** 356 * clocksource_unregister - remove a registered clocksource 357 */ 358 void clocksource_unregister(struct clocksource *cs) 359 { 360 unsigned long flags; 361 362 spin_lock_irqsave(&clocksource_lock, flags); 363 list_del(&cs->list); 364 if (clocksource_override == cs) 365 clocksource_override = NULL; 366 next_clocksource = select_clocksource(); 367 spin_unlock_irqrestore(&clocksource_lock, flags); 368 } 369 370 #ifdef CONFIG_SYSFS 371 /** 372 * sysfs_show_current_clocksources - sysfs interface for current clocksource 373 * @dev: unused 374 * @buf: char buffer to be filled with clocksource list 375 * 376 * Provides sysfs interface for listing current clocksource. 377 */ 378 static ssize_t 379 sysfs_show_current_clocksources(struct sys_device *dev, 380 struct sysdev_attribute *attr, char *buf) 381 { 382 ssize_t count = 0; 383 384 spin_lock_irq(&clocksource_lock); 385 count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name); 386 spin_unlock_irq(&clocksource_lock); 387 388 return count; 389 } 390 391 /** 392 * sysfs_override_clocksource - interface for manually overriding clocksource 393 * @dev: unused 394 * @buf: name of override clocksource 395 * @count: length of buffer 396 * 397 * Takes input from sysfs interface for manually overriding the default 398 * clocksource selction. 399 */ 400 static ssize_t sysfs_override_clocksource(struct sys_device *dev, 401 struct sysdev_attribute *attr, 402 const char *buf, size_t count) 403 { 404 struct clocksource *ovr = NULL; 405 size_t ret = count; 406 int len; 407 408 /* strings from sysfs write are not 0 terminated! */ 409 if (count >= sizeof(override_name)) 410 return -EINVAL; 411 412 /* strip of \n: */ 413 if (buf[count-1] == '\n') 414 count--; 415 416 spin_lock_irq(&clocksource_lock); 417 418 if (count > 0) 419 memcpy(override_name, buf, count); 420 override_name[count] = 0; 421 422 len = strlen(override_name); 423 if (len) { 424 struct clocksource *cs; 425 426 ovr = clocksource_override; 427 /* try to select it: */ 428 list_for_each_entry(cs, &clocksource_list, list) { 429 if (strlen(cs->name) == len && 430 !strcmp(cs->name, override_name)) 431 ovr = cs; 432 } 433 } 434 435 /* Reselect, when the override name has changed */ 436 if (ovr != clocksource_override) { 437 clocksource_override = ovr; 438 next_clocksource = select_clocksource(); 439 } 440 441 spin_unlock_irq(&clocksource_lock); 442 443 return ret; 444 } 445 446 /** 447 * sysfs_show_available_clocksources - sysfs interface for listing clocksource 448 * @dev: unused 449 * @buf: char buffer to be filled with clocksource list 450 * 451 * Provides sysfs interface for listing registered clocksources 452 */ 453 static ssize_t 454 sysfs_show_available_clocksources(struct sys_device *dev, 455 struct sysdev_attribute *attr, 456 char *buf) 457 { 458 struct clocksource *src; 459 ssize_t count = 0; 460 461 spin_lock_irq(&clocksource_lock); 462 list_for_each_entry(src, &clocksource_list, list) { 463 count += snprintf(buf + count, 464 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), 465 "%s ", src->name); 466 } 467 spin_unlock_irq(&clocksource_lock); 468 469 count += snprintf(buf + count, 470 max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n"); 471 472 return count; 473 } 474 475 /* 476 * Sysfs setup bits: 477 */ 478 static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources, 479 sysfs_override_clocksource); 480 481 static SYSDEV_ATTR(available_clocksource, 0444, 482 sysfs_show_available_clocksources, NULL); 483 484 static struct sysdev_class clocksource_sysclass = { 485 .name = "clocksource", 486 }; 487 488 static struct sys_device device_clocksource = { 489 .id = 0, 490 .cls = &clocksource_sysclass, 491 }; 492 493 static int __init init_clocksource_sysfs(void) 494 { 495 int error = sysdev_class_register(&clocksource_sysclass); 496 497 if (!error) 498 error = sysdev_register(&device_clocksource); 499 if (!error) 500 error = sysdev_create_file( 501 &device_clocksource, 502 &attr_current_clocksource); 503 if (!error) 504 error = sysdev_create_file( 505 &device_clocksource, 506 &attr_available_clocksource); 507 return error; 508 } 509 510 device_initcall(init_clocksource_sysfs); 511 #endif /* CONFIG_SYSFS */ 512 513 /** 514 * boot_override_clocksource - boot clock override 515 * @str: override name 516 * 517 * Takes a clocksource= boot argument and uses it 518 * as the clocksource override name. 519 */ 520 static int __init boot_override_clocksource(char* str) 521 { 522 unsigned long flags; 523 spin_lock_irqsave(&clocksource_lock, flags); 524 if (str) 525 strlcpy(override_name, str, sizeof(override_name)); 526 spin_unlock_irqrestore(&clocksource_lock, flags); 527 return 1; 528 } 529 530 __setup("clocksource=", boot_override_clocksource); 531 532 /** 533 * boot_override_clock - Compatibility layer for deprecated boot option 534 * @str: override name 535 * 536 * DEPRECATED! Takes a clock= boot argument and uses it 537 * as the clocksource override name 538 */ 539 static int __init boot_override_clock(char* str) 540 { 541 if (!strcmp(str, "pmtmr")) { 542 printk("Warning: clock=pmtmr is deprecated. " 543 "Use clocksource=acpi_pm.\n"); 544 return boot_override_clocksource("acpi_pm"); 545 } 546 printk("Warning! clock= boot option is deprecated. " 547 "Use clocksource=xyz\n"); 548 return boot_override_clocksource(str); 549 } 550 551 __setup("clock=", boot_override_clock); 552