blob: 5f4a7f72f3ee4adc4729dfdedd71f227091d70a0 [file] [log] [blame]
john stultz734efb42006-06-26 00:25:05 -07001/* 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 */
19typedef 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 */
52struct 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 */
77static 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 */
103static 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/**
john stultza2752542006-06-26 00:25:14 -0700121 * clocksource_read: - Access the clocksource's current cycle value
john stultz734efb42006-06-26 00:25:05 -0700122 * @cs: pointer to clocksource being read
123 *
124 * Uses the clocksource to return the current cycle_t value
125 */
john stultza2752542006-06-26 00:25:14 -0700126static inline cycle_t clocksource_read(struct clocksource *cs)
john stultz734efb42006-06-26 00:25:05 -0700127{
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 */
140static 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/**
john stultza2752542006-06-26 00:25:14 -0700148 * clocksource_calculate_interval - Calculates a clocksource interval struct
john stultz734efb42006-06-26 00:25:05 -0700149 *
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 */
john stultza2752542006-06-26 00:25:14 -0700158static inline void clocksource_calculate_interval(struct clocksource *c,
john stultz734efb42006-06-26 00:25:05 -0700159 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
john stultz5eb6d202006-06-26 00:25:07 -0700176
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 */
189static 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 */
240static 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
john stultz734efb42006-06-26 00:25:05 -0700273/* used to install a new clocksource */
john stultza2752542006-06-26 00:25:14 -0700274int clocksource_register(struct clocksource*);
275void clocksource_reselect(void);
276struct clocksource* clocksource_get_next(void);
john stultz734efb42006-06-26 00:25:05 -0700277
278#endif /* _LINUX_CLOCKSOURCE_H */