1 /* linux/include/linux/clocksource.h
3 * This file contains the structure definitions for clocksources.
5 * If you are not a clocksource, or timekeeping code, you should
6 * not be including this file!
8 #ifndef _LINUX_CLOCKSOURCE_H
9 #define _LINUX_CLOCKSOURCE_H
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>
18 /* clocksource cycle base type */
22 * struct clocksource - hardware abstraction for a free running counter
23 * Provides mostly state-free accessors to the underlying hardware.
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.
36 * A correct and usable clocksource.
38 * A reasonably fast and accurate clocksource.
40 * The ideal clocksource. A must-use where
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 * @flags: flags describing special properties
49 * @cycle_interval: Used internally by timekeeping core, please ignore.
50 * @xtime_interval: Used internally by timekeeping core, please ignore.
54 struct list_head list;
56 cycle_t (*read)(void);
60 int (*update_callback)(void);
63 /* timekeeping specific data, ignore */
64 cycle_t cycle_last, cycle_interval;
65 u64 xtime_nsec, xtime_interval;
70 * Clock source flags bits::
72 #define CLOCK_SOURCE_IS_CONTINUOUS 0x01
73 #define CLOCK_SOURCE_MUST_VERIFY 0x02
75 /* simplify initialization of mask field */
76 #define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
79 * clocksource_khz2mult - calculates mult from khz and shift
80 * @khz: Clocksource frequency in KHz
81 * @shift_constant: Clocksource shift factor
83 * Helper functions that converts a khz counter frequency to a timsource
84 * multiplier, given the clocksource shift value
86 static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
88 /* khz = cyc/(Million ns)
89 * mult/2^shift = ns/cyc
90 * mult = ns/cyc * 2^shift
91 * mult = 1Million/khz * 2^shift
92 * mult = 1000000 * 2^shift / khz
93 * mult = (1000000<<shift) / khz
95 u64 tmp = ((u64)1000000) << shift_constant;
97 tmp += khz/2; /* round for do_div */
104 * clocksource_hz2mult - calculates mult from hz and shift
105 * @hz: Clocksource frequency in Hz
106 * @shift_constant: Clocksource shift factor
108 * Helper functions that converts a hz counter
109 * frequency to a timsource multiplier, given the
110 * clocksource shift value
112 static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
114 /* hz = cyc/(Billion ns)
115 * mult/2^shift = ns/cyc
116 * mult = ns/cyc * 2^shift
117 * mult = 1Billion/hz * 2^shift
118 * mult = 1000000000 * 2^shift / hz
119 * mult = (1000000000<<shift) / hz
121 u64 tmp = ((u64)1000000000) << shift_constant;
123 tmp += hz/2; /* round for do_div */
130 * clocksource_read: - Access the clocksource's current cycle value
131 * @cs: pointer to clocksource being read
133 * Uses the clocksource to return the current cycle_t value
135 static inline cycle_t clocksource_read(struct clocksource *cs)
141 * cyc2ns - converts clocksource cycles to nanoseconds
142 * @cs: Pointer to clocksource
145 * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
147 * XXX - This could use some mult_lxl_ll() asm optimization
149 static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
151 u64 ret = (u64)cycles;
152 ret = (ret * cs->mult) >> cs->shift;
157 * clocksource_calculate_interval - Calculates a clocksource interval struct
159 * @c: Pointer to clocksource.
160 * @length_nsec: Desired interval length in nanoseconds.
162 * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
163 * pair and interval request.
165 * Unless you're the timekeeping code, you should not be using this!
167 static inline void clocksource_calculate_interval(struct clocksource *c,
168 unsigned long length_nsec)
172 /* XXX - All of this could use a whole lot of optimization */
176 do_div(tmp, c->mult);
178 c->cycle_interval = (cycle_t)tmp;
179 if (c->cycle_interval == 0)
180 c->cycle_interval = 1;
182 c->xtime_interval = (u64)c->cycle_interval * c->mult;
186 /* used to install a new clocksource */
187 extern int clocksource_register(struct clocksource*);
188 extern struct clocksource* clocksource_get_next(void);
189 extern void clocksource_change_rating(struct clocksource *cs, int rating);
191 #endif /* _LINUX_CLOCKSOURCE_H */