summaryrefslogtreecommitdiffstats
path: root/kernel/time/clocksource.c
blob: 22504afc0d34b48bf10e216c72b33c3be4470598 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
/*
 * linux/kernel/time/clocksource.c
 *
 * This file contains the functions which manage clocksource drivers.
 *
 * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * TODO WishList:
 *   o Allow clocksource drivers to be unregistered
 *   o get rid of clocksource_jiffies extern
 */

#include <linux/clocksource.h>
#include <linux/sysdev.h>
#include <linux/init.h>
#include <linux/module.h>

/* XXX - Would like a better way for initializing curr_clocksource */
extern struct clocksource clocksource_jiffies;

/*[Clocksource internal variables]---------
 * curr_clocksource:
 *	currently selected clocksource. Initialized to clocksource_jiffies.
 * next_clocksource:
 *	pending next selected clocksource.
 * clocksource_list:
 *	linked list with the registered clocksources
 * clocksource_lock:
 *	protects manipulations to curr_clocksource and next_clocksource
 *	and the clocksource_list
 * override_name:
 *	Name of the user-specified clocksource.
 */
static struct clocksource *curr_clocksource = &clocksource_jiffies;
static struct clocksource *next_clocksource;
static LIST_HEAD(clocksource_list);
static DEFINE_SPINLOCK(clocksource_lock);
static char override_name[32];
static int finished_booting;

/* clocksource_done_booting - Called near the end of bootup
 *
 * Hack to avoid lots of clocksource churn at boot time
 */
static int __init clocksource_done_booting(void)
{
	finished_booting = 1;
	return 0;
}

late_initcall(clocksource_done_booting);

/**
 * clocksource_get_next - Returns the selected clocksource
 *
 */
struct clocksource *clocksource_get_next(void)
{
	unsigned long flags;

	spin_lock_irqsave(&clocksource_lock, flags);
	if (next_clocksource && finished_booting) {
		curr_clocksource = next_clocksource;
		next_clocksource = NULL;
	}
	spin_unlock_irqrestore(&clocksource_lock, flags);

	return curr_clocksource;
}

/**
 * select_clocksource - Finds the best registered clocksource.
 *
 * Private function. Must hold clocksource_lock when called.
 *
 * Looks through the list of registered clocksources, returning
 * the one with the highest rating value. If there is a clocksource
 * name that matches the override string, it returns that clocksource.
 */
static struct clocksource *select_clocksource(void)
{
	struct clocksource *best = NULL;
	struct list_head *tmp;

	list_for_each(tmp, &clocksource_list) {
		struct clocksource *src;

		src = list_entry(tmp, struct clocksource, list);
		if (!best)
			best = src;

		/* check for override: */
		if (strlen(src->name) == strlen(override_name) &&
		    !strcmp(src->name, override_name)) {
			best = src;
			break;
		}
		/* pick the highest rating: */
		if (src->rating > best->rating)
		 	best = src;
	}

	return best;
}

/**
 * is_registered_source - Checks if clocksource is registered
 * @c:		pointer to a clocksource
 *
 * Private helper function. Must hold clocksource_lock when called.
 *
 * Returns one if the clocksource is already registered, zero otherwise.
 */
static int is_registered_source(struct clocksource *c)
{
	int len = strlen(c->name);
	struct list_head *tmp;

	list_for_each(tmp, &clocksource_list) {
		struct clocksource *src;

		src = list_entry(tmp, struct clocksource, list);
		if (strlen(src->name) == len &&	!strcmp(src->name, c->name))
			return 1;
	}

	return 0;
}

/**
 * clocksource_register - Used to install new clocksources
 * @t:		clocksource to be registered
 *
 * Returns -EBUSY if registration fails, zero otherwise.
 */
int clocksource_register(struct clocksource *c)
{
	int ret = 0;
	unsigned long flags;

	spin_lock_irqsave(&clocksource_lock, flags);
	/* check if clocksource is already registered */
	if (is_registered_source(c)) {
		printk("register_clocksource: Cannot register %s. "
		       "Already registered!", c->name);
		ret = -EBUSY;
	} else {
		/* register it */
 		list_add(&c->list, &clocksource_list);
		/* scan the registered clocksources, and pick the best one */
		next_clocksource = select_clocksource();
	}
	spin_unlock_irqrestore(&clocksource_lock, flags);
	return ret;
}
EXPORT_SYMBOL(clocksource_register);

/**
 * clocksource_reselect - Rescan list for next clocksource
 *
 * A quick helper function to be used if a clocksource changes its
 * rating. Forces the clocksource list to be re-scanned for the best
 * clocksource.
 */
void clocksource_reselect(void)
{
	unsigned long flags;

	spin_lock_irqsave(&clocksource_lock, flags);
	next_clocksource = select_clocksource();
	spin_unlock_irqrestore(&clocksource_lock, flags);
}
EXPORT_SYMBOL(clocksource_reselect);

#ifdef CONFIG_SYSFS
/**
 * sysfs_show_current_clocksources - sysfs interface for current clocksource
 * @dev:	unused
 * @buf:	char buffer to be filled with clocksource list
 *
 * Provides sysfs interface for listing current clocksource.
 */
static ssize_t
sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
{
	char *curr = buf;

	spin_lock_irq(&clocksource_lock);
	curr += sprintf(curr, "%s ", curr_clocksource->name);
	spin_unlock_irq(&clocksource_lock);

	curr += sprintf(curr, "\n");

	return curr - buf;
}

/**
 * sysfs_override_clocksource - interface for manually overriding clocksource
 * @dev:	unused
 * @buf:	name of override clocksource
 * @count:	length of buffer
 *
 * Takes input from sysfs interface for manually overriding the default
 * clocksource selction.
 */
static ssize_t sysfs_override_clocksource(struct sys_device *dev,
					  const char *buf, size_t count)
{
	size_t ret = count;
	/* strings from sysfs write are not 0 terminated! */
	if (count >= sizeof(override_name))
		return -EINVAL;

	/* strip of \n: */
	if (buf[count-1] == '\n')
		count--;
	if (count < 1)
		return -EINVAL;

	spin_lock_irq(&clocksource_lock);

	/* copy the name given: */
	memcpy(override_name, buf, count);
	override_name[count] = 0;

	/* try to select it: */
	next_clocksource = select_clocksource();

	spin_unlock_irq(&clocksource_lock);

	return ret;
}

/**
 * sysfs_show_available_clocksources - sysfs interface for listing clocksource
 * @dev:	unused
 * @buf:	char buffer to be filled with clocksource list
 *
 * Provides sysfs interface for listing registered clocksources
 */
static ssize_t
sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
{
	struct list_head *tmp;
	char *curr = buf;

	spin_lock_irq(&clocksource_lock);
	list_for_each(tmp, &clocksource_list) {
		struct clocksource *src;

		src = list_entry(tmp, struct clocksource, list);
		curr += sprintf(curr, "%s ", src->name);
	}
	spin_unlock_irq(&clocksource_lock);

	curr += sprintf(curr, "\n");

	return curr - buf;
}

/*
 * Sysfs setup bits:
 */
static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
		   sysfs_override_clocksource);

static SYSDEV_ATTR(available_clocksource, 0600,
		   sysfs_show_available_clocksources, NULL);

static struct sysdev_class clocksource_sysclass = {
	set_kset_name("clocksource"),
};

static struct sys_device device_clocksource = {
	.id	= 0,
	.cls	= &clocksource_sysclass,
};

static int __init init_clocksource_sysfs(void)
{
	int error = sysdev_class_register(&clocksource_sysclass);

	if (!error)
		error = sysdev_register(&device_clocksource);
	if (!error)
		error = sysdev_create_file(
				&device_clocksource,
				&attr_current_clocksource);
	if (!error)
		error = sysdev_create_file(
				&device_clocksource,
				&attr_available_clocksource);
	return error;
}

device_initcall(init_clocksource_sysfs);
#endif /* CONFIG_SYSFS */

/**
 * boot_override_clocksource - boot clock override
 * @str:	override name
 *
 * Takes a clocksource= boot argument and uses it
 * as the clocksource override name.
 */
static int __init boot_override_clocksource(char* str)
{
	unsigned long flags;
	spin_lock_irqsave(&clocksource_lock, flags);
	if (str)
		strlcpy(override_name, str, sizeof(override_name));
	spin_unlock_irqrestore(&clocksource_lock, flags);
	return 1;
}

__setup("clocksource=", boot_override_clocksource);

/**
 * boot_override_clock - Compatibility layer for deprecated boot option
 * @str:	override name
 *
 * DEPRECATED! Takes a clock= boot argument and uses it
 * as the clocksource override name
 */
static int __init boot_override_clock(char* str)
{
	if (!strcmp(str, "pmtmr")) {
		printk("Warning: clock=pmtmr is deprecated. "
			"Use clocksource=acpi_pm.\n");
		return boot_override_clocksource("acpi_pm");
	}
	printk("Warning! clock= boot option is deprecated. "
		"Use clocksource=xyz\n");
	return boot_override_clocksource(str);
}

__setup("clock=", boot_override_clock);