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734efb46 | 1 | /* linux/include/linux/clocksource.h |
2 | * | |
3 | * This file contains the structure definitions for clocksources. | |
4 | * | |
5 | * If you are not a clocksource, or timekeeping code, you should | |
6 | * not be including this file! | |
7 | */ | |
8 | #ifndef _LINUX_CLOCKSOURCE_H | |
9 | #define _LINUX_CLOCKSOURCE_H | |
10 | ||
11 | #include <linux/types.h> | |
12 | #include <linux/timex.h> | |
13 | #include <linux/time.h> | |
14 | #include <linux/list.h> | |
15 | #include <asm/div64.h> | |
16 | #include <asm/io.h> | |
17 | ||
18 | /* clocksource cycle base type */ | |
19 | typedef u64 cycle_t; | |
20 | ||
21 | /** | |
22 | * struct clocksource - hardware abstraction for a free running counter | |
23 | * Provides mostly state-free accessors to the underlying hardware. | |
24 | * | |
25 | * @name: ptr to clocksource name | |
26 | * @list: list head for registration | |
27 | * @rating: rating value for selection (higher is better) | |
28 | * To avoid rating inflation the following | |
29 | * list should give you a guide as to how | |
30 | * to assign your clocksource a rating | |
31 | * 1-99: Unfit for real use | |
32 | * Only available for bootup and testing purposes. | |
33 | * 100-199: Base level usability. | |
34 | * Functional for real use, but not desired. | |
35 | * 200-299: Good. | |
36 | * A correct and usable clocksource. | |
37 | * 300-399: Desired. | |
38 | * A reasonably fast and accurate clocksource. | |
39 | * 400-499: Perfect | |
40 | * The ideal clocksource. A must-use where | |
41 | * available. | |
42 | * @read: returns a cycle value | |
43 | * @mask: bitmask for two's complement | |
44 | * subtraction of non 64 bit counters | |
45 | * @mult: cycle to nanosecond multiplier | |
46 | * @shift: cycle to nanosecond divisor (power of two) | |
47 | * @update_callback: called when safe to alter clocksource values | |
48 | * @is_continuous: defines if clocksource is free-running. | |
49 | * @interval_cycles: Used internally by timekeeping core, please ignore. | |
50 | * @interval_snsecs: Used internally by timekeeping core, please ignore. | |
51 | */ | |
52 | struct clocksource { | |
53 | char *name; | |
54 | struct list_head list; | |
55 | int rating; | |
56 | cycle_t (*read)(void); | |
57 | cycle_t mask; | |
58 | u32 mult; | |
59 | u32 shift; | |
60 | int (*update_callback)(void); | |
61 | int is_continuous; | |
62 | ||
63 | /* timekeeping specific data, ignore */ | |
64 | cycle_t interval_cycles; | |
65 | u64 interval_snsecs; | |
66 | }; | |
67 | ||
7f9f303a JC |
68 | /* simplify initialization of mask field */ |
69 | #define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1) | |
734efb46 | 70 | |
71 | /** | |
72 | * clocksource_khz2mult - calculates mult from khz and shift | |
73 | * @khz: Clocksource frequency in KHz | |
74 | * @shift_constant: Clocksource shift factor | |
75 | * | |
76 | * Helper functions that converts a khz counter frequency to a timsource | |
77 | * multiplier, given the clocksource shift value | |
78 | */ | |
79 | static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant) | |
80 | { | |
81 | /* khz = cyc/(Million ns) | |
82 | * mult/2^shift = ns/cyc | |
83 | * mult = ns/cyc * 2^shift | |
84 | * mult = 1Million/khz * 2^shift | |
85 | * mult = 1000000 * 2^shift / khz | |
86 | * mult = (1000000<<shift) / khz | |
87 | */ | |
88 | u64 tmp = ((u64)1000000) << shift_constant; | |
89 | ||
90 | tmp += khz/2; /* round for do_div */ | |
91 | do_div(tmp, khz); | |
92 | ||
93 | return (u32)tmp; | |
94 | } | |
95 | ||
96 | /** | |
97 | * clocksource_hz2mult - calculates mult from hz and shift | |
98 | * @hz: Clocksource frequency in Hz | |
99 | * @shift_constant: Clocksource shift factor | |
100 | * | |
101 | * Helper functions that converts a hz counter | |
102 | * frequency to a timsource multiplier, given the | |
103 | * clocksource shift value | |
104 | */ | |
105 | static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant) | |
106 | { | |
107 | /* hz = cyc/(Billion ns) | |
108 | * mult/2^shift = ns/cyc | |
109 | * mult = ns/cyc * 2^shift | |
110 | * mult = 1Billion/hz * 2^shift | |
111 | * mult = 1000000000 * 2^shift / hz | |
112 | * mult = (1000000000<<shift) / hz | |
113 | */ | |
114 | u64 tmp = ((u64)1000000000) << shift_constant; | |
115 | ||
116 | tmp += hz/2; /* round for do_div */ | |
117 | do_div(tmp, hz); | |
118 | ||
119 | return (u32)tmp; | |
120 | } | |
121 | ||
122 | /** | |
a2752549 | 123 | * clocksource_read: - Access the clocksource's current cycle value |
734efb46 | 124 | * @cs: pointer to clocksource being read |
125 | * | |
126 | * Uses the clocksource to return the current cycle_t value | |
127 | */ | |
a2752549 | 128 | static inline cycle_t clocksource_read(struct clocksource *cs) |
734efb46 | 129 | { |
130 | return cs->read(); | |
131 | } | |
132 | ||
133 | /** | |
134 | * cyc2ns - converts clocksource cycles to nanoseconds | |
135 | * @cs: Pointer to clocksource | |
136 | * @cycles: Cycles | |
137 | * | |
138 | * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds. | |
139 | * | |
140 | * XXX - This could use some mult_lxl_ll() asm optimization | |
141 | */ | |
142 | static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles) | |
143 | { | |
144 | u64 ret = (u64)cycles; | |
145 | ret = (ret * cs->mult) >> cs->shift; | |
146 | return ret; | |
147 | } | |
148 | ||
149 | /** | |
a2752549 | 150 | * clocksource_calculate_interval - Calculates a clocksource interval struct |
734efb46 | 151 | * |
152 | * @c: Pointer to clocksource. | |
153 | * @length_nsec: Desired interval length in nanoseconds. | |
154 | * | |
155 | * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment | |
156 | * pair and interval request. | |
157 | * | |
158 | * Unless you're the timekeeping code, you should not be using this! | |
159 | */ | |
a2752549 | 160 | static inline void clocksource_calculate_interval(struct clocksource *c, |
734efb46 | 161 | unsigned long length_nsec) |
162 | { | |
163 | u64 tmp; | |
164 | ||
165 | /* XXX - All of this could use a whole lot of optimization */ | |
166 | tmp = length_nsec; | |
167 | tmp <<= c->shift; | |
168 | tmp += c->mult/2; | |
169 | do_div(tmp, c->mult); | |
170 | ||
171 | c->interval_cycles = (cycle_t)tmp; | |
172 | if(c->interval_cycles == 0) | |
173 | c->interval_cycles = 1; | |
174 | ||
175 | c->interval_snsecs = (u64)c->interval_cycles * c->mult; | |
176 | } | |
177 | ||
5eb6d205 | 178 | |
179 | /** | |
180 | * error_aproximation - calculates an error adjustment for a given error | |
181 | * | |
182 | * @error: Error value (unsigned) | |
183 | * @unit: Adjustment unit | |
184 | * | |
185 | * For a given error value, this function takes the adjustment unit | |
186 | * and uses binary approximation to return a power of two adjustment value. | |
187 | * | |
188 | * This function is only for use by the the make_ntp_adj() function | |
189 | * and you must hold a write on the xtime_lock when calling. | |
190 | */ | |
191 | static inline int error_aproximation(u64 error, u64 unit) | |
192 | { | |
193 | static int saved_adj = 0; | |
194 | u64 adjusted_unit = unit << saved_adj; | |
195 | ||
196 | if (error > (adjusted_unit * 2)) { | |
197 | /* large error, so increment the adjustment factor */ | |
198 | saved_adj++; | |
199 | } else if (error > adjusted_unit) { | |
200 | /* just right, don't touch it */ | |
201 | } else if (saved_adj) { | |
202 | /* small error, so drop the adjustment factor */ | |
203 | saved_adj--; | |
204 | return 0; | |
205 | } | |
206 | ||
207 | return saved_adj; | |
208 | } | |
209 | ||
210 | ||
211 | /** | |
212 | * make_ntp_adj - Adjusts the specified clocksource for a given error | |
213 | * | |
214 | * @clock: Pointer to clock to be adjusted | |
215 | * @cycles_delta: Current unacounted cycle delta | |
216 | * @error: Pointer to current error value | |
217 | * | |
218 | * Returns clock shifted nanosecond adjustment to be applied against | |
219 | * the accumulated time value (ie: xtime). | |
220 | * | |
221 | * If the error value is large enough, this function calulates the | |
222 | * (power of two) adjustment value, and adjusts the clock's mult and | |
223 | * interval_snsecs values accordingly. | |
224 | * | |
225 | * However, since there may be some unaccumulated cycles, to avoid | |
226 | * time inconsistencies we must adjust the accumulation value | |
227 | * accordingly. | |
228 | * | |
229 | * This is not very intuitive, so the following proof should help: | |
230 | * The basic timeofday algorithm: base + cycle * mult | |
231 | * Thus: | |
232 | * new_base + cycle * new_mult = old_base + cycle * old_mult | |
233 | * new_base = old_base + cycle * old_mult - cycle * new_mult | |
234 | * new_base = old_base + cycle * (old_mult - new_mult) | |
235 | * new_base - old_base = cycle * (old_mult - new_mult) | |
236 | * base_delta = cycle * (old_mult - new_mult) | |
237 | * base_delta = cycle * (mult_delta) | |
238 | * | |
239 | * Where mult_delta is the adjustment value made to mult | |
240 | * | |
241 | */ | |
242 | static inline s64 make_ntp_adj(struct clocksource *clock, | |
243 | cycles_t cycles_delta, s64* error) | |
244 | { | |
245 | s64 ret = 0; | |
246 | if (*error > ((s64)clock->interval_cycles+1)/2) { | |
247 | /* calculate adjustment value */ | |
248 | int adjustment = error_aproximation(*error, | |
249 | clock->interval_cycles); | |
250 | /* adjust clock */ | |
251 | clock->mult += 1 << adjustment; | |
252 | clock->interval_snsecs += clock->interval_cycles << adjustment; | |
253 | ||
254 | /* adjust the base and error for the adjustment */ | |
255 | ret = -(cycles_delta << adjustment); | |
256 | *error -= clock->interval_cycles << adjustment; | |
257 | /* XXX adj error for cycle_delta offset? */ | |
258 | } else if ((-(*error)) > ((s64)clock->interval_cycles+1)/2) { | |
259 | /* calculate adjustment value */ | |
260 | int adjustment = error_aproximation(-(*error), | |
261 | clock->interval_cycles); | |
262 | /* adjust clock */ | |
263 | clock->mult -= 1 << adjustment; | |
264 | clock->interval_snsecs -= clock->interval_cycles << adjustment; | |
265 | ||
266 | /* adjust the base and error for the adjustment */ | |
267 | ret = cycles_delta << adjustment; | |
268 | *error += clock->interval_cycles << adjustment; | |
269 | /* XXX adj error for cycle_delta offset? */ | |
270 | } | |
271 | return ret; | |
272 | } | |
273 | ||
274 | ||
734efb46 | 275 | /* used to install a new clocksource */ |
a2752549 | 276 | int clocksource_register(struct clocksource*); |
277 | void clocksource_reselect(void); | |
278 | struct clocksource* clocksource_get_next(void); | |
734efb46 | 279 | |
280 | #endif /* _LINUX_CLOCKSOURCE_H */ |