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 <linux/cache.h>
16 #include <linux/timer.h>
17 #include <asm/div64.h>
20 /* clocksource cycle base type */
25 * struct clocksource - hardware abstraction for a free running counter
26 * Provides mostly state-free accessors to the underlying hardware.
28 * @name: ptr to clocksource name
29 * @list: list head for registration
30 * @rating: rating value for selection (higher is better)
31 * To avoid rating inflation the following
32 * list should give you a guide as to how
33 * to assign your clocksource a rating
34 * 1-99: Unfit for real use
35 * Only available for bootup and testing purposes.
36 * 100-199: Base level usability.
37 * Functional for real use, but not desired.
39 * A correct and usable clocksource.
41 * A reasonably fast and accurate clocksource.
43 * The ideal clocksource. A must-use where
45 * @read: returns a cycle value
46 * @mask: bitmask for two's complement
47 * subtraction of non 64 bit counters
48 * @mult: cycle to nanosecond multiplier
49 * @shift: cycle to nanosecond divisor (power of two)
50 * @flags: flags describing special properties
51 * @vread: vsyscall based read
52 * @cycle_interval: Used internally by timekeeping core, please ignore.
53 * @xtime_interval: Used internally by timekeeping core, please ignore.
57 * First part of structure is read mostly
60 struct list_head list
;
62 cycle_t (*read
)(void);
67 cycle_t (*vread
)(void);
69 /* timekeeping specific data, ignore */
70 cycle_t cycle_interval
;
73 * Second part is written at each timer interrupt
74 * Keep it in a different cache line to dirty no
75 * more than one cache line.
77 cycle_t cycle_last ____cacheline_aligned_in_smp
;
81 #ifdef CONFIG_CLOCKSOURCE_WATCHDOG
82 /* Watchdog related data, used by the framework */
83 struct list_head wd_list
;
89 * Clock source flags bits::
91 #define CLOCK_SOURCE_IS_CONTINUOUS 0x01
92 #define CLOCK_SOURCE_MUST_VERIFY 0x02
94 #define CLOCK_SOURCE_WATCHDOG 0x10
95 #define CLOCK_SOURCE_VALID_FOR_HRES 0x20
97 /* simplify initialization of mask field */
98 #define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
101 * clocksource_khz2mult - calculates mult from khz and shift
102 * @khz: Clocksource frequency in KHz
103 * @shift_constant: Clocksource shift factor
105 * Helper functions that converts a khz counter frequency to a timsource
106 * multiplier, given the clocksource shift value
108 static inline u32
clocksource_khz2mult(u32 khz
, u32 shift_constant
)
110 /* khz = cyc/(Million ns)
111 * mult/2^shift = ns/cyc
112 * mult = ns/cyc * 2^shift
113 * mult = 1Million/khz * 2^shift
114 * mult = 1000000 * 2^shift / khz
115 * mult = (1000000<<shift) / khz
117 u64 tmp
= ((u64
)1000000) << shift_constant
;
119 tmp
+= khz
/2; /* round for do_div */
126 * clocksource_hz2mult - calculates mult from hz and shift
127 * @hz: Clocksource frequency in Hz
128 * @shift_constant: Clocksource shift factor
130 * Helper functions that converts a hz counter
131 * frequency to a timsource multiplier, given the
132 * clocksource shift value
134 static inline u32
clocksource_hz2mult(u32 hz
, u32 shift_constant
)
136 /* hz = cyc/(Billion ns)
137 * mult/2^shift = ns/cyc
138 * mult = ns/cyc * 2^shift
139 * mult = 1Billion/hz * 2^shift
140 * mult = 1000000000 * 2^shift / hz
141 * mult = (1000000000<<shift) / hz
143 u64 tmp
= ((u64
)1000000000) << shift_constant
;
145 tmp
+= hz
/2; /* round for do_div */
152 * clocksource_read: - Access the clocksource's current cycle value
153 * @cs: pointer to clocksource being read
155 * Uses the clocksource to return the current cycle_t value
157 static inline cycle_t
clocksource_read(struct clocksource
*cs
)
163 * cyc2ns - converts clocksource cycles to nanoseconds
164 * @cs: Pointer to clocksource
167 * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
169 * XXX - This could use some mult_lxl_ll() asm optimization
171 static inline s64
cyc2ns(struct clocksource
*cs
, cycle_t cycles
)
173 u64 ret
= (u64
)cycles
;
174 ret
= (ret
* cs
->mult
) >> cs
->shift
;
179 * clocksource_calculate_interval - Calculates a clocksource interval struct
181 * @c: Pointer to clocksource.
182 * @length_nsec: Desired interval length in nanoseconds.
184 * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
185 * pair and interval request.
187 * Unless you're the timekeeping code, you should not be using this!
189 static inline void clocksource_calculate_interval(struct clocksource
*c
,
190 unsigned long length_nsec
)
194 /* XXX - All of this could use a whole lot of optimization */
198 do_div(tmp
, c
->mult
);
200 c
->cycle_interval
= (cycle_t
)tmp
;
201 if (c
->cycle_interval
== 0)
202 c
->cycle_interval
= 1;
204 c
->xtime_interval
= (u64
)c
->cycle_interval
* c
->mult
;
208 /* used to install a new clocksource */
209 extern int clocksource_register(struct clocksource
*);
210 extern struct clocksource
* clocksource_get_next(void);
211 extern void clocksource_change_rating(struct clocksource
*cs
, int rating
);
213 #ifdef CONFIG_GENERIC_TIME_VSYSCALL
214 extern void update_vsyscall(struct timespec
*ts
, struct clocksource
*c
);
216 static inline void update_vsyscall(struct timespec
*ts
, struct clocksource
*c
)
221 #endif /* _LINUX_CLOCKSOURCE_H */