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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> |
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31 | #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */ |
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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 | */ |
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60 | static int __init clocksource_done_booting(void) |
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61 | { |
62 | finished_booting = 1; |
63 | return 0; |
64 | } |
65 | |
66 | late_initcall(clocksource_done_booting); |
67 | |
68 | /** |
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69 | * clocksource_get_next - Returns the selected clocksource |
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70 | * |
71 | */ |
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72 | struct clocksource *clocksource_get_next(void) |
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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 | /** |
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146 | * clocksource_register - Used to install new clocksources |
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147 | * @t: clocksource to be registered |
148 | * |
149 | * Returns -EBUSY if registration fails, zero otherwise. |
150 | */ |
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151 | int clocksource_register(struct clocksource *c) |
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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. " |
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160 | "Already registered!", c->name); |
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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 | } |
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171 | EXPORT_SYMBOL(clocksource_register); |
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172 | |
173 | /** |
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174 | * clocksource_reselect - Rescan list for next clocksource |
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175 | * |
176 | * A quick helper function to be used if a clocksource changes its |
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177 | * rating. Forces the clocksource list to be re-scanned for the best |
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178 | * clocksource. |
179 | */ |
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180 | void clocksource_reselect(void) |
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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 | } |
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188 | EXPORT_SYMBOL(clocksource_reselect); |
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189 | |
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190 | #ifdef CONFIG_SYSFS |
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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, |
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280 | sysfs_override_clocksource); |
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281 | |
282 | static SYSDEV_ATTR(available_clocksource, 0600, |
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283 | sysfs_show_available_clocksources, NULL); |
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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 | |
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294 | static int __init init_clocksource_sysfs(void) |
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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); |
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312 | #endif /* CONFIG_SYSFS */ |
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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 | { |
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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"); |
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349 | return boot_override_clocksource(str); |
350 | } |
351 | |
352 | __setup("clock=", boot_override_clock); |