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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 | |
68 | |
69 | /** |
70 | * clocksource_khz2mult - calculates mult from khz and shift |
71 | * @khz: Clocksource frequency in KHz |
72 | * @shift_constant: Clocksource shift factor |
73 | * |
74 | * Helper functions that converts a khz counter frequency to a timsource |
75 | * multiplier, given the clocksource shift value |
76 | */ |
77 | static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant) |
78 | { |
79 | /* khz = cyc/(Million ns) |
80 | * mult/2^shift = ns/cyc |
81 | * mult = ns/cyc * 2^shift |
82 | * mult = 1Million/khz * 2^shift |
83 | * mult = 1000000 * 2^shift / khz |
84 | * mult = (1000000<<shift) / khz |
85 | */ |
86 | u64 tmp = ((u64)1000000) << shift_constant; |
87 | |
88 | tmp += khz/2; /* round for do_div */ |
89 | do_div(tmp, khz); |
90 | |
91 | return (u32)tmp; |
92 | } |
93 | |
94 | /** |
95 | * clocksource_hz2mult - calculates mult from hz and shift |
96 | * @hz: Clocksource frequency in Hz |
97 | * @shift_constant: Clocksource shift factor |
98 | * |
99 | * Helper functions that converts a hz counter |
100 | * frequency to a timsource multiplier, given the |
101 | * clocksource shift value |
102 | */ |
103 | static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant) |
104 | { |
105 | /* hz = cyc/(Billion ns) |
106 | * mult/2^shift = ns/cyc |
107 | * mult = ns/cyc * 2^shift |
108 | * mult = 1Billion/hz * 2^shift |
109 | * mult = 1000000000 * 2^shift / hz |
110 | * mult = (1000000000<<shift) / hz |
111 | */ |
112 | u64 tmp = ((u64)1000000000) << shift_constant; |
113 | |
114 | tmp += hz/2; /* round for do_div */ |
115 | do_div(tmp, hz); |
116 | |
117 | return (u32)tmp; |
118 | } |
119 | |
120 | /** |
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121 | * clocksource_read: - Access the clocksource's current cycle value |
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122 | * @cs: pointer to clocksource being read |
123 | * |
124 | * Uses the clocksource to return the current cycle_t value |
125 | */ |
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126 | static inline cycle_t clocksource_read(struct clocksource *cs) |
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127 | { |
128 | return cs->read(); |
129 | } |
130 | |
131 | /** |
132 | * cyc2ns - converts clocksource cycles to nanoseconds |
133 | * @cs: Pointer to clocksource |
134 | * @cycles: Cycles |
135 | * |
136 | * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds. |
137 | * |
138 | * XXX - This could use some mult_lxl_ll() asm optimization |
139 | */ |
140 | static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles) |
141 | { |
142 | u64 ret = (u64)cycles; |
143 | ret = (ret * cs->mult) >> cs->shift; |
144 | return ret; |
145 | } |
146 | |
147 | /** |
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148 | * clocksource_calculate_interval - Calculates a clocksource interval struct |
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149 | * |
150 | * @c: Pointer to clocksource. |
151 | * @length_nsec: Desired interval length in nanoseconds. |
152 | * |
153 | * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment |
154 | * pair and interval request. |
155 | * |
156 | * Unless you're the timekeeping code, you should not be using this! |
157 | */ |
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158 | static inline void clocksource_calculate_interval(struct clocksource *c, |
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159 | unsigned long length_nsec) |
160 | { |
161 | u64 tmp; |
162 | |
163 | /* XXX - All of this could use a whole lot of optimization */ |
164 | tmp = length_nsec; |
165 | tmp <<= c->shift; |
166 | tmp += c->mult/2; |
167 | do_div(tmp, c->mult); |
168 | |
169 | c->interval_cycles = (cycle_t)tmp; |
170 | if(c->interval_cycles == 0) |
171 | c->interval_cycles = 1; |
172 | |
173 | c->interval_snsecs = (u64)c->interval_cycles * c->mult; |
174 | } |
175 | |
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176 | |
177 | /** |
178 | * error_aproximation - calculates an error adjustment for a given error |
179 | * |
180 | * @error: Error value (unsigned) |
181 | * @unit: Adjustment unit |
182 | * |
183 | * For a given error value, this function takes the adjustment unit |
184 | * and uses binary approximation to return a power of two adjustment value. |
185 | * |
186 | * This function is only for use by the the make_ntp_adj() function |
187 | * and you must hold a write on the xtime_lock when calling. |
188 | */ |
189 | static inline int error_aproximation(u64 error, u64 unit) |
190 | { |
191 | static int saved_adj = 0; |
192 | u64 adjusted_unit = unit << saved_adj; |
193 | |
194 | if (error > (adjusted_unit * 2)) { |
195 | /* large error, so increment the adjustment factor */ |
196 | saved_adj++; |
197 | } else if (error > adjusted_unit) { |
198 | /* just right, don't touch it */ |
199 | } else if (saved_adj) { |
200 | /* small error, so drop the adjustment factor */ |
201 | saved_adj--; |
202 | return 0; |
203 | } |
204 | |
205 | return saved_adj; |
206 | } |
207 | |
208 | |
209 | /** |
210 | * make_ntp_adj - Adjusts the specified clocksource for a given error |
211 | * |
212 | * @clock: Pointer to clock to be adjusted |
213 | * @cycles_delta: Current unacounted cycle delta |
214 | * @error: Pointer to current error value |
215 | * |
216 | * Returns clock shifted nanosecond adjustment to be applied against |
217 | * the accumulated time value (ie: xtime). |
218 | * |
219 | * If the error value is large enough, this function calulates the |
220 | * (power of two) adjustment value, and adjusts the clock's mult and |
221 | * interval_snsecs values accordingly. |
222 | * |
223 | * However, since there may be some unaccumulated cycles, to avoid |
224 | * time inconsistencies we must adjust the accumulation value |
225 | * accordingly. |
226 | * |
227 | * This is not very intuitive, so the following proof should help: |
228 | * The basic timeofday algorithm: base + cycle * mult |
229 | * Thus: |
230 | * new_base + cycle * new_mult = old_base + cycle * old_mult |
231 | * new_base = old_base + cycle * old_mult - cycle * new_mult |
232 | * new_base = old_base + cycle * (old_mult - new_mult) |
233 | * new_base - old_base = cycle * (old_mult - new_mult) |
234 | * base_delta = cycle * (old_mult - new_mult) |
235 | * base_delta = cycle * (mult_delta) |
236 | * |
237 | * Where mult_delta is the adjustment value made to mult |
238 | * |
239 | */ |
240 | static inline s64 make_ntp_adj(struct clocksource *clock, |
241 | cycles_t cycles_delta, s64* error) |
242 | { |
243 | s64 ret = 0; |
244 | if (*error > ((s64)clock->interval_cycles+1)/2) { |
245 | /* calculate adjustment value */ |
246 | int adjustment = error_aproximation(*error, |
247 | clock->interval_cycles); |
248 | /* adjust clock */ |
249 | clock->mult += 1 << adjustment; |
250 | clock->interval_snsecs += clock->interval_cycles << adjustment; |
251 | |
252 | /* adjust the base and error for the adjustment */ |
253 | ret = -(cycles_delta << adjustment); |
254 | *error -= clock->interval_cycles << adjustment; |
255 | /* XXX adj error for cycle_delta offset? */ |
256 | } else if ((-(*error)) > ((s64)clock->interval_cycles+1)/2) { |
257 | /* calculate adjustment value */ |
258 | int adjustment = error_aproximation(-(*error), |
259 | clock->interval_cycles); |
260 | /* adjust clock */ |
261 | clock->mult -= 1 << adjustment; |
262 | clock->interval_snsecs -= clock->interval_cycles << adjustment; |
263 | |
264 | /* adjust the base and error for the adjustment */ |
265 | ret = cycles_delta << adjustment; |
266 | *error += clock->interval_cycles << adjustment; |
267 | /* XXX adj error for cycle_delta offset? */ |
268 | } |
269 | return ret; |
270 | } |
271 | |
272 | |
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273 | /* used to install a new clocksource */ |
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274 | int clocksource_register(struct clocksource*); |
275 | void clocksource_reselect(void); |
276 | struct clocksource* clocksource_get_next(void); |
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277 | |
278 | #endif /* _LINUX_CLOCKSOURCE_H */ |