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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 */ |
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 | */ |
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59 | static int __init clocksource_done_booting(void) |
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60 | { |
61 | finished_booting = 1; |
62 | return 0; |
63 | } |
64 | |
65 | late_initcall(clocksource_done_booting); |
66 | |
67 | /** |
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68 | * clocksource_get_next - Returns the selected clocksource |
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69 | * |
70 | */ |
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71 | struct clocksource *clocksource_get_next(void) |
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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 | /** |
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145 | * clocksource_register - Used to install new clocksources |
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146 | * @t: clocksource to be registered |
147 | * |
148 | * Returns -EBUSY if registration fails, zero otherwise. |
149 | */ |
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150 | int clocksource_register(struct clocksource *c) |
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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 | } |
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170 | EXPORT_SYMBOL(clocksource_register); |
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171 | |
172 | /** |
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173 | * clocksource_reselect - Rescan list for next clocksource |
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174 | * |
175 | * A quick helper function to be used if a clocksource changes its |
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176 | * rating. Forces the clocksource list to be re-scanned for the best |
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177 | * clocksource. |
178 | */ |
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179 | void clocksource_reselect(void) |
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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 | } |
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187 | EXPORT_SYMBOL(clocksource_reselect); |
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188 | |
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189 | #ifdef CONFIG_SYSFS |
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190 | /** |
191 | * sysfs_show_current_clocksources - sysfs interface for current clocksource |
192 | * @dev: unused |
193 | * @buf: char buffer to be filled with clocksource list |
194 | * |
195 | * Provides sysfs interface for listing current clocksource. |
196 | */ |
197 | static ssize_t |
198 | sysfs_show_current_clocksources(struct sys_device *dev, char *buf) |
199 | { |
200 | char *curr = buf; |
201 | |
202 | spin_lock_irq(&clocksource_lock); |
203 | curr += sprintf(curr, "%s ", curr_clocksource->name); |
204 | spin_unlock_irq(&clocksource_lock); |
205 | |
206 | curr += sprintf(curr, "\n"); |
207 | |
208 | return curr - buf; |
209 | } |
210 | |
211 | /** |
212 | * sysfs_override_clocksource - interface for manually overriding clocksource |
213 | * @dev: unused |
214 | * @buf: name of override clocksource |
215 | * @count: length of buffer |
216 | * |
217 | * Takes input from sysfs interface for manually overriding the default |
218 | * clocksource selction. |
219 | */ |
220 | static ssize_t sysfs_override_clocksource(struct sys_device *dev, |
221 | const char *buf, size_t count) |
222 | { |
223 | size_t ret = count; |
224 | /* strings from sysfs write are not 0 terminated! */ |
225 | if (count >= sizeof(override_name)) |
226 | return -EINVAL; |
227 | |
228 | /* strip of \n: */ |
229 | if (buf[count-1] == '\n') |
230 | count--; |
231 | if (count < 1) |
232 | return -EINVAL; |
233 | |
234 | spin_lock_irq(&clocksource_lock); |
235 | |
236 | /* copy the name given: */ |
237 | memcpy(override_name, buf, count); |
238 | override_name[count] = 0; |
239 | |
240 | /* try to select it: */ |
241 | next_clocksource = select_clocksource(); |
242 | |
243 | spin_unlock_irq(&clocksource_lock); |
244 | |
245 | return ret; |
246 | } |
247 | |
248 | /** |
249 | * sysfs_show_available_clocksources - sysfs interface for listing clocksource |
250 | * @dev: unused |
251 | * @buf: char buffer to be filled with clocksource list |
252 | * |
253 | * Provides sysfs interface for listing registered clocksources |
254 | */ |
255 | static ssize_t |
256 | sysfs_show_available_clocksources(struct sys_device *dev, char *buf) |
257 | { |
258 | struct list_head *tmp; |
259 | char *curr = buf; |
260 | |
261 | spin_lock_irq(&clocksource_lock); |
262 | list_for_each(tmp, &clocksource_list) { |
263 | struct clocksource *src; |
264 | |
265 | src = list_entry(tmp, struct clocksource, list); |
266 | curr += sprintf(curr, "%s ", src->name); |
267 | } |
268 | spin_unlock_irq(&clocksource_lock); |
269 | |
270 | curr += sprintf(curr, "\n"); |
271 | |
272 | return curr - buf; |
273 | } |
274 | |
275 | /* |
276 | * Sysfs setup bits: |
277 | */ |
278 | static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources, |
279 | sysfs_override_clocksource); |
280 | |
281 | static SYSDEV_ATTR(available_clocksource, 0600, |
282 | sysfs_show_available_clocksources, NULL); |
283 | |
284 | static struct sysdev_class clocksource_sysclass = { |
285 | set_kset_name("clocksource"), |
286 | }; |
287 | |
288 | static struct sys_device device_clocksource = { |
289 | .id = 0, |
290 | .cls = &clocksource_sysclass, |
291 | }; |
292 | |
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293 | static int __init init_clocksource_sysfs(void) |
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294 | { |
295 | int error = sysdev_class_register(&clocksource_sysclass); |
296 | |
297 | if (!error) |
298 | error = sysdev_register(&device_clocksource); |
299 | if (!error) |
300 | error = sysdev_create_file( |
301 | &device_clocksource, |
302 | &attr_current_clocksource); |
303 | if (!error) |
304 | error = sysdev_create_file( |
305 | &device_clocksource, |
306 | &attr_available_clocksource); |
307 | return error; |
308 | } |
309 | |
310 | device_initcall(init_clocksource_sysfs); |
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311 | #endif /* CONFIG_SYSFS */ |
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312 | |
313 | /** |
314 | * boot_override_clocksource - boot clock override |
315 | * @str: override name |
316 | * |
317 | * Takes a clocksource= boot argument and uses it |
318 | * as the clocksource override name. |
319 | */ |
320 | static int __init boot_override_clocksource(char* str) |
321 | { |
322 | unsigned long flags; |
323 | spin_lock_irqsave(&clocksource_lock, flags); |
324 | if (str) |
325 | strlcpy(override_name, str, sizeof(override_name)); |
326 | spin_unlock_irqrestore(&clocksource_lock, flags); |
327 | return 1; |
328 | } |
329 | |
330 | __setup("clocksource=", boot_override_clocksource); |
331 | |
332 | /** |
333 | * boot_override_clock - Compatibility layer for deprecated boot option |
334 | * @str: override name |
335 | * |
336 | * DEPRECATED! Takes a clock= boot argument and uses it |
337 | * as the clocksource override name |
338 | */ |
339 | static int __init boot_override_clock(char* str) |
340 | { |
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341 | if (!strcmp(str, "pmtmr")) { |
342 | printk("Warning: clock=pmtmr is deprecated. " |
343 | "Use clocksource=acpi_pm.\n"); |
344 | return boot_override_clocksource("acpi_pm"); |
345 | } |
346 | printk("Warning! clock= boot option is deprecated. " |
347 | "Use clocksource=xyz\n"); |
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348 | return boot_override_clocksource(str); |
349 | } |
350 | |
351 | __setup("clock=", boot_override_clock); |