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authorjohn stultz <johnstul@us.ibm.com>2006-06-26 03:25:05 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-26 12:58:20 -0400
commit734efb467b31e56c2f9430590a9aa867ecf3eea1 (patch)
tree30bf6b52d1e67128e656fb9a01cd7e6e13b7755e /kernel/time/clocksource.c
parentade1a29e168ba08b699a418ff5e762315fa33f70 (diff)
[PATCH] Time: Clocksource Infrastructure
This introduces the clocksource management infrastructure. A clocksource is a driver-like architecture generic abstraction of a free-running counter. This code defines the clocksource structure, and provides management code for registering, selecting, accessing and scaling clocksources. Additionally, this includes the trivial jiffies clocksource, a lowest common denominator clocksource, provided mainly for use as an example. [hirofumi@mail.parknet.co.jp: Don't enable IRQ too early] Signed-off-by: John Stultz <johnstul@us.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Paul Mundt <lethal@linux-sh.org> Signed-off-by: John Stultz <johnstul@us.ibm.com> Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel/time/clocksource.c')
-rw-r--r--kernel/time/clocksource.c344
1 files changed, 344 insertions, 0 deletions
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
new file mode 100644
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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 */
33extern 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 */
48static struct clocksource *curr_clocksource = &clocksource_jiffies;
49static struct clocksource *next_clocksource;
50static LIST_HEAD(clocksource_list);
51static DEFINE_SPINLOCK(clocksource_lock);
52static char override_name[32];
53static 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 */
59static int clocksource_done_booting(void)
60{
61 finished_booting = 1;
62 return 0;
63}
64
65late_initcall(clocksource_done_booting);
66
67/**
68 * get_next_clocksource - Returns the selected clocksource
69 *
70 */
71struct clocksource *get_next_clocksource(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 */
94static 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 */
128static 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 * register_clocksource - Used to install new clocksources
146 * @t: clocksource to be registered
147 *
148 * Returns -EBUSY if registration fails, zero otherwise.
149 */
150int register_clocksource(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
171EXPORT_SYMBOL(register_clocksource);
172
173/**
174 * reselect_clocksource - 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-scaned for the best
178 * clocksource.
179 */
180void reselect_clocksource(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
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 */
196static ssize_t
197sysfs_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 */
219static 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 */
254static ssize_t
255sysfs_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 */
277static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
278 sysfs_override_clocksource);
279
280static SYSDEV_ATTR(available_clocksource, 0600,
281 sysfs_show_available_clocksources, NULL);
282
283static struct sysdev_class clocksource_sysclass = {
284 set_kset_name("clocksource"),
285};
286
287static struct sys_device device_clocksource = {
288 .id = 0,
289 .cls = &clocksource_sysclass,
290};
291
292static int 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
309device_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 */
318static 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 */
337static int __init boot_override_clock(char* str)
338{
339 printk("Warning! clock= boot option is deprecated.\n");
340
341 return boot_override_clocksource(str);
342}
343
344__setup("clock=", boot_override_clock);