ia64/linux-2.6.18-xen.hg

view kernel/time/clocksource.c @ 562:66faefe721eb

pvSCSI backend driver

Signed-off-by: Tomonari Horikoshi <t.horikoshi@jp.fujitsu.com>
Signed-off-by: Jun Kamada <kama@jp.fujitsu.com>
author Keir Fraser <keir.fraser@citrix.com>
date Mon Jun 02 09:58:27 2008 +0100 (2008-06-02)
parents 831230e53067
children
line source
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 */
27 #include <linux/clocksource.h>
28 #include <linux/sysdev.h>
29 #include <linux/init.h>
30 #include <linux/module.h>
32 /* XXX - Would like a better way for initializing curr_clocksource */
33 extern struct clocksource clocksource_jiffies;
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;
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 }
65 late_initcall(clocksource_done_booting);
67 /**
68 * clocksource_get_next - Returns the selected clocksource
69 *
70 */
71 struct clocksource *clocksource_get_next(void)
72 {
73 unsigned long flags;
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);
82 return curr_clocksource;
83 }
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;
99 list_for_each(tmp, &clocksource_list) {
100 struct clocksource *src;
102 src = list_entry(tmp, struct clocksource, list);
103 if (!best)
104 best = src;
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 }
117 return best;
118 }
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;
133 list_for_each(tmp, &clocksource_list) {
134 struct clocksource *src;
136 src = list_entry(tmp, struct clocksource, list);
137 if (strlen(src->name) == len && !strcmp(src->name, c->name))
138 return 1;
139 }
141 return 0;
142 }
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;
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);
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;
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);
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;
201 spin_lock_irq(&clocksource_lock);
202 curr += sprintf(curr, "%s ", curr_clocksource->name);
203 spin_unlock_irq(&clocksource_lock);
205 curr += sprintf(curr, "\n");
207 return curr - buf;
208 }
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;
227 /* strip of \n: */
228 if (buf[count-1] == '\n')
229 count--;
230 if (count < 1)
231 return -EINVAL;
233 spin_lock_irq(&clocksource_lock);
235 /* copy the name given: */
236 memcpy(override_name, buf, count);
237 override_name[count] = 0;
239 /* try to select it: */
240 next_clocksource = select_clocksource();
242 spin_unlock_irq(&clocksource_lock);
244 return ret;
245 }
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;
260 spin_lock_irq(&clocksource_lock);
261 list_for_each(tmp, &clocksource_list) {
262 struct clocksource *src;
264 src = list_entry(tmp, struct clocksource, list);
265 curr += sprintf(curr, "%s ", src->name);
266 }
267 spin_unlock_irq(&clocksource_lock);
269 curr += sprintf(curr, "\n");
271 return curr - buf;
272 }
274 /*
275 * Sysfs setup bits:
276 */
277 static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
278 sysfs_override_clocksource);
280 static SYSDEV_ATTR(available_clocksource, 0600,
281 sysfs_show_available_clocksources, NULL);
283 static struct sysdev_class clocksource_sysclass = {
284 set_kset_name("clocksource"),
285 };
287 static struct sys_device device_clocksource = {
288 .id = 0,
289 .cls = &clocksource_sysclass,
290 };
292 static int __init init_clocksource_sysfs(void)
293 {
294 int error = sysdev_class_register(&clocksource_sysclass);
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 }
309 device_initcall(init_clocksource_sysfs);
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 }
328 __setup("clocksource=", boot_override_clocksource);
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 }
349 __setup("clock=", boot_override_clock);