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
  33 /* XXX - Would like a better way for initializing curr_clocksource */
  34 extern struct clocksource clocksource_jiffies;
  35
  36 /*[Clocksource internal variables]---------
  37  * curr_clocksource:
  38  *      currently selected clocksource. Initialized to clocksource_jiffies.
  39  * next_clocksource:
  40  *      pending next selected clocksource.
  41  * clocksource_list:
  42  *      linked list with the registered clocksources
  43  * clocksource_lock:
  44  *      protects manipulations to curr_clocksource and next_clocksource
  45  *      and the clocksource_list
  46  * override_name:
  47  *      Name of the user-specified clocksource.
  48  */
  49 static struct clocksource *curr_clocksource = &clocksource_jiffies;
  50 static struct clocksource *next_clocksource;
  51 static LIST_HEAD(clocksource_list);
  52 static DEFINE_SPINLOCK(clocksource_lock);
  53 static char override_name[32];
  54 static int finished_booting;
  55
  56 /* clocksource_done_booting - Called near the end of bootup
  57  *
  58  * Hack to avoid lots of clocksource churn at boot time
  59  */
  60 static int __init clocksource_done_booting(void)
  61 {
  62         finished_booting = 1;
  63         return 0;
  64 }
  65
  66 late_initcall(clocksource_done_booting);
  67
  68 /**
  69  * clocksource_get_next - Returns the selected clocksource
  70  *
  71  */
  72 struct clocksource *clocksource_get_next(void)
  73 {
  74         unsigned long flags;
  75
  76         spin_lock_irqsave(&clocksource_lock, flags);
  77         if (next_clocksource && finished_booting) {
  78                 curr_clocksource = next_clocksource;
  79                 next_clocksource = NULL;
  80         }
  81         spin_unlock_irqrestore(&clocksource_lock, flags);
  82
  83         return curr_clocksource;
  84 }
  85
  86 /**
  87  * select_clocksource - Finds the best registered clocksource.
  88  *
  89  * Private function. Must hold clocksource_lock when called.
  90  *
  91  * Looks through the list of registered clocksources, returning
  92  * the one with the highest rating value. If there is a clocksource
  93  * name that matches the override string, it returns that clocksource.
  94  */
  95 static struct clocksource *select_clocksource(void)
  96 {
  97         struct clocksource *best = NULL;
  98         struct list_head *tmp;
  99
 100         list_for_each(tmp, &clocksource_list) {
 101                 struct clocksource *src;
 102
 103                 src = list_entry(tmp, struct clocksource, list);
 104                 if (!best)
 105                         best = src;
 106
 107                 /* check for override: */
 108                 if (strlen(src->name) == strlen(override_name) &&
 109                     !strcmp(src->name, override_name)) {
 110                         best = src;
 111                         break;
 112                 }
 113                 /* pick the highest rating: */
 114                 if (src->rating > best->rating)
 115                         best = src;
 116         }
 117
 118         return best;
 119 }
 120
 121 /**
 122  * is_registered_source - Checks if clocksource is registered
 123  * @c:          pointer to a clocksource
 124  *
 125  * Private helper function. Must hold clocksource_lock when called.
 126  *
 127  * Returns one if the clocksource is already registered, zero otherwise.
 128  */
 129 static int is_registered_source(struct clocksource *c)
 130 {
 131         int len = strlen(c->name);
 132         struct list_head *tmp;
 133
 134         list_for_each(tmp, &clocksource_list) {
 135                 struct clocksource *src;
 136
 137                 src = list_entry(tmp, struct clocksource, list);
 138                 if (strlen(src->name) == len && !strcmp(src->name, c->name))
 139                         return 1;
 140         }
 141
 142         return 0;
 143 }
 144
 145 /**
 146  * clocksource_register - Used to install new clocksources
 147  * @t:          clocksource to be registered
 148  *
 149  * Returns -EBUSY if registration fails, zero otherwise.
 150  */
 151 int clocksource_register(struct clocksource *c)
 152 {
 153         int ret = 0;
 154         unsigned long flags;
 155
 156         spin_lock_irqsave(&clocksource_lock, flags);
 157         /* check if clocksource is already registered */
 158         if (is_registered_source(c)) {
 159                 printk("register_clocksource: Cannot register %s. "
 160                        "Already registered!", c->name);
 161                 ret = -EBUSY;
 162         } else {
 163                 /* register it */
 164                 list_add(&c->list, &clocksource_list);
 165                 /* scan the registered clocksources, and pick the best one */
 166                 next_clocksource = select_clocksource();
 167         }
 168         spin_unlock_irqrestore(&clocksource_lock, flags);
 169         return ret;
 170 }
 171 EXPORT_SYMBOL(clocksource_register);
 172
 173 /**
 174  * clocksource_reselect - Rescan list for next clocksource
 175  *
 176  * A quick helper function to be used if a clocksource changes its
 177  * rating. Forces the clocksource list to be re-scanned for the best
 178  * clocksource.
 179  */
 180 void clocksource_reselect(void)
 181 {
 182         unsigned long flags;
 183
 184         spin_lock_irqsave(&clocksource_lock, flags);
 185         next_clocksource = select_clocksource();
 186         spin_unlock_irqrestore(&clocksource_lock, flags);
 187 }
 188 EXPORT_SYMBOL(clocksource_reselect);
 189
 190 #ifdef CONFIG_SYSFS
 191 /**
 192  * sysfs_show_current_clocksources - sysfs interface for current clocksource
 193  * @dev:        unused
 194  * @buf:        char buffer to be filled with clocksource list
 195  *
 196  * Provides sysfs interface for listing current clocksource.
 197  */
 198 static ssize_t
 199 sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
 200 {
 201         char *curr = buf;
 202
 203         spin_lock_irq(&clocksource_lock);
 204         curr += sprintf(curr, "%s ", curr_clocksource->name);
 205         spin_unlock_irq(&clocksource_lock);
 206
 207         curr += sprintf(curr, "\n");
 208
 209         return curr - buf;
 210 }
 211
 212 /**
 213  * sysfs_override_clocksource - interface for manually overriding clocksource
 214  * @dev:        unused
 215  * @buf:        name of override clocksource
 216  * @count:      length of buffer
 217  *
 218  * Takes input from sysfs interface for manually overriding the default
 219  * clocksource selction.
 220  */
 221 static ssize_t sysfs_override_clocksource(struct sys_device *dev,
 222                                           const char *buf, size_t count)
 223 {
 224         size_t ret = count;
 225         /* strings from sysfs write are not 0 terminated! */
 226         if (count >= sizeof(override_name))
 227                 return -EINVAL;
 228
 229         /* strip of \n: */
 230         if (buf[count-1] == '\n')
 231                 count--;
 232         if (count < 1)
 233                 return -EINVAL;
 234
 235         spin_lock_irq(&clocksource_lock);
 236
 237         /* copy the name given: */
 238         memcpy(override_name, buf, count);
 239         override_name[count] = 0;
 240
 241         /* try to select it: */
 242         next_clocksource = select_clocksource();
 243
 244         spin_unlock_irq(&clocksource_lock);
 245
 246         return ret;
 247 }
 248
 249 /**
 250  * sysfs_show_available_clocksources - sysfs interface for listing clocksource
 251  * @dev:        unused
 252  * @buf:        char buffer to be filled with clocksource list
 253  *
 254  * Provides sysfs interface for listing registered clocksources
 255  */
 256 static ssize_t
 257 sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
 258 {
 259         struct list_head *tmp;
 260         char *curr = buf;
 261
 262         spin_lock_irq(&clocksource_lock);
 263         list_for_each(tmp, &clocksource_list) {
 264                 struct clocksource *src;
 265
 266                 src = list_entry(tmp, struct clocksource, list);
 267                 curr += sprintf(curr, "%s ", src->name);
 268         }
 269         spin_unlock_irq(&clocksource_lock);
 270
 271         curr += sprintf(curr, "\n");
 272
 273         return curr - buf;
 274 }
 275
 276 /*
 277  * Sysfs setup bits:
 278  */
 279 static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
 280                    sysfs_override_clocksource);
 281
 282 static SYSDEV_ATTR(available_clocksource, 0600,
 283                    sysfs_show_available_clocksources, NULL);
 284
 285 static struct sysdev_class clocksource_sysclass = {
 286         set_kset_name("clocksource"),
 287 };
 288
 289 static struct sys_device device_clocksource = {
 290         .id     = 0,
 291         .cls    = &clocksource_sysclass,
 292 };
 293
 294 static int __init init_clocksource_sysfs(void)
 295 {
 296         int error = sysdev_class_register(&clocksource_sysclass);
 297
 298         if (!error)
 299                 error = sysdev_register(&device_clocksource);
 300         if (!error)
 301                 error = sysdev_create_file(
 302                                 &device_clocksource,
 303                                 &attr_current_clocksource);
 304         if (!error)
 305                 error = sysdev_create_file(
 306                                 &device_clocksource,
 307                                 &attr_available_clocksource);
 308         return error;
 309 }
 310
 311 device_initcall(init_clocksource_sysfs);
 312 #endif /* CONFIG_SYSFS */
 313
 314 /**
 315  * boot_override_clocksource - boot clock override
 316  * @str:        override name
 317  *
 318  * Takes a clocksource= boot argument and uses it
 319  * as the clocksource override name.
 320  */
 321 static int __init boot_override_clocksource(char* str)
 322 {
 323         unsigned long flags;
 324         spin_lock_irqsave(&clocksource_lock, flags);
 325         if (str)
 326                 strlcpy(override_name, str, sizeof(override_name));
 327         spin_unlock_irqrestore(&clocksource_lock, flags);
 328         return 1;
 329 }
 330
 331 __setup("clocksource=", boot_override_clocksource);
 332
 333 /**
 334  * boot_override_clock - Compatibility layer for deprecated boot option
 335  * @str:        override name
 336  *
 337  * DEPRECATED! Takes a clock= boot argument and uses it
 338  * as the clocksource override name
 339  */
 340 static int __init boot_override_clock(char* str)
 341 {
 342         if (!strcmp(str, "pmtmr")) {
 343                 printk("Warning: clock=pmtmr is deprecated. "
 344                         "Use clocksource=acpi_pm.\n");
 345                 return boot_override_clocksource("acpi_pm");
 346         }
 347         printk("Warning! clock= boot option is deprecated. "
 348                 "Use clocksource=xyz\n");
 349         return boot_override_clocksource(str);
 350 }
 351
 352 __setup("clock=", boot_override_clock);