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
  32 /* XXX - Would like a better way for initializing curr_clocksource */
  33 extern struct clocksource clocksource_jiffies;
  34
  35 /*[Clocksource internal variables]---------
  36  * curr_clocksource:
  37  *      currently selected clocksource. Initialized to clocksource_jiffies.
  38  * next_clocksource:
  39  *      pending next selected clocksource.
  40  * clocksource_list:
  41  *      linked list with the registered clocksources
  42  * clocksource_lock:
  43  *      protects manipulations to curr_clocksource and next_clocksource
  44  *      and the clocksource_list
  45  * override_name:
  46  *      Name of the user-specified clocksource.
  47  */
  48 static struct clocksource *curr_clocksource = &clocksource_jiffies;
  49 static struct clocksource *next_clocksource;
  50 static LIST_HEAD(clocksource_list);
  51 static DEFINE_SPINLOCK(clocksource_lock);
  52 static char override_name[32];
  53 static int finished_booting;
  54
  55 /* clocksource_done_booting - Called near the end of bootup
  56  *
  57  * Hack to avoid lots of clocksource churn at boot time
  58  */
  59 static int __init clocksource_done_booting(void)
  60 {
  61         finished_booting = 1;
  62         return 0;
  63 }
  64
  65 late_initcall(clocksource_done_booting);
  66
  67 /**
  68  * clocksource_get_next - Returns the selected clocksource
  69  *
  70  */
  71 struct clocksource *clocksource_get_next(void)
  72 {
  73         unsigned long flags;
  74
  75         spin_lock_irqsave(&clocksource_lock, flags);
  76         if (next_clocksource && finished_booting) {
  77                 curr_clocksource = next_clocksource;
  78                 next_clocksource = NULL;
  79         }
  80         spin_unlock_irqrestore(&clocksource_lock, flags);
  81
  82         return curr_clocksource;
  83 }
  84
  85 /**
  86  * select_clocksource - Finds the best registered clocksource.
  87  *
  88  * Private function. Must hold clocksource_lock when called.
  89  *
  90  * Looks through the list of registered clocksources, returning
  91  * the one with the highest rating value. If there is a clocksource
  92  * name that matches the override string, it returns that clocksource.
  93  */
  94 static struct clocksource *select_clocksource(void)
  95 {
  96         struct clocksource *best = NULL;
  97         struct list_head *tmp;
  98
  99         list_for_each(tmp, &clocksource_list) {
 100                 struct clocksource *src;
 101
 102                 src = list_entry(tmp, struct clocksource, list);
 103                 if (!best)
 104                         best = src;
 105
 106                 /* check for override: */
 107                 if (strlen(src->name) == strlen(override_name) &&
 108                     !strcmp(src->name, override_name)) {
 109                         best = src;
 110                         break;
 111                 }
 112                 /* pick the highest rating: */
 113                 if (src->rating > best->rating)
 114                         best = src;
 115         }
 116
 117         return best;
 118 }
 119
 120 /**
 121  * is_registered_source - Checks if clocksource is registered
 122  * @c:          pointer to a clocksource
 123  *
 124  * Private helper function. Must hold clocksource_lock when called.
 125  *
 126  * Returns one if the clocksource is already registered, zero otherwise.
 127  */
 128 static int is_registered_source(struct clocksource *c)
 129 {
 130         int len = strlen(c->name);
 131         struct list_head *tmp;
 132
 133         list_for_each(tmp, &clocksource_list) {
 134                 struct clocksource *src;
 135
 136                 src = list_entry(tmp, struct clocksource, list);
 137                 if (strlen(src->name) == len && !strcmp(src->name, c->name))
 138                         return 1;
 139         }
 140
 141         return 0;
 142 }
 143
 144 /**
 145  * clocksource_register - Used to install new clocksources
 146  * @t:          clocksource to be registered
 147  *
 148  * Returns -EBUSY if registration fails, zero otherwise.
 149  */
 150 int clocksource_register(struct clocksource *c)
 151 {
 152         int ret = 0;
 153         unsigned long flags;
 154
 155         spin_lock_irqsave(&clocksource_lock, flags);
 156         /* check if clocksource is already registered */
 157         if (is_registered_source(c)) {
 158                 printk("register_clocksource: Cannot register %s. "
 159                         "Already registered!", c->name);
 160                 ret = -EBUSY;
 161         } else {
 162                 /* register it */
 163                 list_add(&c->list, &clocksource_list);
 164                 /* scan the registered clocksources, and pick the best one */
 165                 next_clocksource = select_clocksource();
 166         }
 167         spin_unlock_irqrestore(&clocksource_lock, flags);
 168         return ret;
 169 }
 170 EXPORT_SYMBOL(clocksource_register);
 171
 172 /**
 173  * clocksource_reselect - Rescan list for next clocksource
 174  *
 175  * A quick helper function to be used if a clocksource changes its
 176  * rating. Forces the clocksource list to be re-scanned for the best
 177  * clocksource.
 178  */
 179 void clocksource_reselect(void)
 180 {
 181         unsigned long flags;
 182
 183         spin_lock_irqsave(&clocksource_lock, flags);
 184         next_clocksource = select_clocksource();
 185         spin_unlock_irqrestore(&clocksource_lock, flags);
 186 }
 187 EXPORT_SYMBOL(clocksource_reselect);
 188
 189 /**
 190  * sysfs_show_current_clocksources - sysfs interface for current clocksource
 191  * @dev:        unused
 192  * @buf:        char buffer to be filled with clocksource list
 193  *
 194  * Provides sysfs interface for listing current clocksource.
 195  */
 196 static ssize_t
 197 sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
 198 {
 199         char *curr = buf;
 200
 201         spin_lock_irq(&clocksource_lock);
 202         curr += sprintf(curr, "%s ", curr_clocksource->name);
 203         spin_unlock_irq(&clocksource_lock);
 204
 205         curr += sprintf(curr, "\n");
 206
 207         return curr - buf;
 208 }
 209
 210 /**
 211  * sysfs_override_clocksource - interface for manually overriding clocksource
 212  * @dev:        unused
 213  * @buf:        name of override clocksource
 214  * @count:      length of buffer
 215  *
 216  * Takes input from sysfs interface for manually overriding the default
 217  * clocksource selction.
 218  */
 219 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
 220                                           const char *buf, size_t count)
 221 {
 222         size_t ret = count;
 223         /* strings from sysfs write are not 0 terminated! */
 224         if (count >= sizeof(override_name))
 225                 return -EINVAL;
 226
 227         /* strip of \n: */
 228         if (buf[count-1] == '\n')
 229                 count--;
 230         if (count < 1)
 231                 return -EINVAL;
 232
 233         spin_lock_irq(&clocksource_lock);
 234
 235         /* copy the name given: */
 236         memcpy(override_name, buf, count);
 237         override_name[count] = 0;
 238
 239         /* try to select it: */
 240         next_clocksource = select_clocksource();
 241
 242         spin_unlock_irq(&clocksource_lock);
 243
 244         return ret;
 245 }
 246
 247 /**
 248  * sysfs_show_available_clocksources - sysfs interface for listing clocksource
 249  * @dev:        unused
 250  * @buf:        char buffer to be filled with clocksource list
 251  *
 252  * Provides sysfs interface for listing registered clocksources
 253  */
 254 static ssize_t
 255 sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
 256 {
 257         struct list_head *tmp;
 258         char *curr = buf;
 259
 260         spin_lock_irq(&clocksource_lock);
 261         list_for_each(tmp, &clocksource_list) {
 262                 struct clocksource *src;
 263
 264                 src = list_entry(tmp, struct clocksource, list);
 265                 curr += sprintf(curr, "%s ", src->name);
 266         }
 267         spin_unlock_irq(&clocksource_lock);
 268
 269         curr += sprintf(curr, "\n");
 270
 271         return curr - buf;
 272 }
 273
 274 /*
 275  * Sysfs setup bits:
 276  */
 277 static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
 278                         sysfs_override_clocksource);
 279
 280 static SYSDEV_ATTR(available_clocksource, 0600,
 281                         sysfs_show_available_clocksources, NULL);
 282
 283 static struct sysdev_class clocksource_sysclass = {
 284         set_kset_name("clocksource"),
 285 };
 286
 287 static struct sys_device device_clocksource = {
 288         .id     = 0,
 289         .cls    = &clocksource_sysclass,
 290 };
 291
 292 static int __init init_clocksource_sysfs(void)
 293 {
 294         int error = sysdev_class_register(&clocksource_sysclass);
 295
 296         if (!error)
 297                 error = sysdev_register(&device_clocksource);
 298         if (!error)
 299                 error = sysdev_create_file(
 300                                 &device_clocksource,
 301                                 &attr_current_clocksource);
 302         if (!error)
 303                 error = sysdev_create_file(
 304                                 &device_clocksource,
 305                                 &attr_available_clocksource);
 306         return error;
 307 }
 308
 309 device_initcall(init_clocksource_sysfs);
 310
 311 /**
 312  * boot_override_clocksource - boot clock override
 313  * @str:        override name
 314  *
 315  * Takes a clocksource= boot argument and uses it
 316  * as the clocksource override name.
 317  */
 318 static int __init boot_override_clocksource(char* str)
 319 {
 320         unsigned long flags;
 321         spin_lock_irqsave(&clocksource_lock, flags);
 322         if (str)
 323                 strlcpy(override_name, str, sizeof(override_name));
 324         spin_unlock_irqrestore(&clocksource_lock, flags);
 325         return 1;
 326 }
 327
 328 __setup("clocksource=", boot_override_clocksource);
 329
 330 /**
 331  * boot_override_clock - Compatibility layer for deprecated boot option
 332  * @str:        override name
 333  *
 334  * DEPRECATED! Takes a clock= boot argument and uses it
 335  * as the clocksource override name
 336  */
 337 static int __init boot_override_clock(char* str)
 338 {
 339         if (!strcmp(str, "pmtmr")) {
 340                 printk("Warning: clock=pmtmr is deprecated. "
 341                         "Use clocksource=acpi_pm.\n");
 342                 return boot_override_clocksource("acpi_pm");
 343         }
 344         printk("Warning! clock= boot option is deprecated. "
 345                 "Use clocksource=xyz\n");
 346         return boot_override_clocksource(str);
 347 }
 348
 349 __setup("clock=", boot_override_clock);