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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 */
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 * @cycle_interval: Used internally by timekeeping core, please ignore.
50 * @xtime_interval: 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 cycle_last, cycle_interval;
65 u64 xtime_nsec, xtime_interval;
66 s64 error;
67};
68
69/* simplify initialization of mask field */
70#define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
71
72/**
73 * clocksource_khz2mult - calculates mult from khz and shift
74 * @khz: Clocksource frequency in KHz
75 * @shift_constant: Clocksource shift factor
76 *
77 * Helper functions that converts a khz counter frequency to a timsource
78 * multiplier, given the clocksource shift value
79 */
80static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
81{
82 /* khz = cyc/(Million ns)
83 * mult/2^shift = ns/cyc
84 * mult = ns/cyc * 2^shift
85 * mult = 1Million/khz * 2^shift
86 * mult = 1000000 * 2^shift / khz
87 * mult = (1000000<<shift) / khz
88 */
89 u64 tmp = ((u64)1000000) << shift_constant;
90
91 tmp += khz/2; /* round for do_div */
92 do_div(tmp, khz);
93
94 return (u32)tmp;
95}
96
97/**
98 * clocksource_hz2mult - calculates mult from hz and shift
99 * @hz: Clocksource frequency in Hz
100 * @shift_constant: Clocksource shift factor
101 *
102 * Helper functions that converts a hz counter
103 * frequency to a timsource multiplier, given the
104 * clocksource shift value
105 */
106static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
107{
108 /* hz = cyc/(Billion ns)
109 * mult/2^shift = ns/cyc
110 * mult = ns/cyc * 2^shift
111 * mult = 1Billion/hz * 2^shift
112 * mult = 1000000000 * 2^shift / hz
113 * mult = (1000000000<<shift) / hz
114 */
115 u64 tmp = ((u64)1000000000) << shift_constant;
116
117 tmp += hz/2; /* round for do_div */
118 do_div(tmp, hz);
119
120 return (u32)tmp;
121}
122
123/**
124 * clocksource_read: - Access the clocksource's current cycle value
125 * @cs: pointer to clocksource being read
126 *
127 * Uses the clocksource to return the current cycle_t value
128 */
129static inline cycle_t clocksource_read(struct clocksource *cs)
130{
131 return cs->read();
132}
133
134/**
135 * cyc2ns - converts clocksource cycles to nanoseconds
136 * @cs: Pointer to clocksource
137 * @cycles: Cycles
138 *
139 * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
140 *
141 * XXX - This could use some mult_lxl_ll() asm optimization
142 */
143static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
144{
145 u64 ret = (u64)cycles;
146 ret = (ret * cs->mult) >> cs->shift;
147 return ret;
148}
149
150/**
151 * clocksource_calculate_interval - Calculates a clocksource interval struct
152 *
153 * @c: Pointer to clocksource.
154 * @length_nsec: Desired interval length in nanoseconds.
155 *
156 * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
157 * pair and interval request.
158 *
159 * Unless you're the timekeeping code, you should not be using this!
160 */
161static inline void clocksource_calculate_interval(struct clocksource *c,
162 unsigned long length_nsec)
163{
164 u64 tmp;
165
166 /* XXX - All of this could use a whole lot of optimization */
167 tmp = length_nsec;
168 tmp <<= c->shift;
169 tmp += c->mult/2;
170 do_div(tmp, c->mult);
171
172 c->cycle_interval = (cycle_t)tmp;
173 if (c->cycle_interval == 0)
174 c->cycle_interval = 1;
175
176 c->xtime_interval = (u64)c->cycle_interval * c->mult;
177}
178
179
180/* used to install a new clocksource */
181int clocksource_register(struct clocksource*);
182void clocksource_reselect(void);
183struct clocksource* clocksource_get_next(void);
184
185#endif /* _LINUX_CLOCKSOURCE_H */