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 <linux/cache.h>
16#include <linux/timer.h>
17#include <asm/div64.h>
18#include <asm/io.h>
19
20/* clocksource cycle base type */
21typedef u64 cycle_t;
22struct clocksource;
23
24/**
25 * struct clocksource - hardware abstraction for a free running counter
26 *	Provides mostly state-free accessors to the underlying hardware.
27 *
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.
38 *			200-299: Good.
39 *				A correct and usable clocksource.
40 *			300-399: Desired.
41 *				A reasonably fast and accurate clocksource.
42 *			400-499: Perfect
43 *				The ideal clocksource. A must-use where
44 *				available.
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 * @resume:		resume function for the clocksource, if necessary
53 * @cycle_interval:	Used internally by timekeeping core, please ignore.
54 * @xtime_interval:	Used internally by timekeeping core, please ignore.
55 */
56struct clocksource {
57	/*
58	 * First part of structure is read mostly
59	 */
60	char *name;
61	struct list_head list;
62	int rating;
63	cycle_t (*read)(void);
64	cycle_t mask;
65	u32 mult;
66	u32 shift;
67	unsigned long flags;
68	cycle_t (*vread)(void);
69	void (*resume)(void);
70
71	/* timekeeping specific data, ignore */
72	cycle_t cycle_interval;
73	u64	xtime_interval;
74	/*
75	 * Second part is written at each timer interrupt
76	 * Keep it in a different cache line to dirty no
77	 * more than one cache line.
78	 */
79	cycle_t cycle_last ____cacheline_aligned_in_smp;
80	u64 xtime_nsec;
81	s64 error;
82
83#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
84	/* Watchdog related data, used by the framework */
85	struct list_head wd_list;
86	cycle_t wd_last;
87#endif
88};
89
90/*
91 * Clock source flags bits::
92 */
93#define CLOCK_SOURCE_IS_CONTINUOUS		0x01
94#define CLOCK_SOURCE_MUST_VERIFY		0x02
95
96#define CLOCK_SOURCE_WATCHDOG			0x10
97#define CLOCK_SOURCE_VALID_FOR_HRES		0x20
98
99/* simplify initialization of mask field */
100#define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
101
102/**
103 * clocksource_khz2mult - calculates mult from khz and shift
104 * @khz:		Clocksource frequency in KHz
105 * @shift_constant:	Clocksource shift factor
106 *
107 * Helper functions that converts a khz counter frequency to a timsource
108 * multiplier, given the clocksource shift value
109 */
110static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
111{
112	/*  khz = cyc/(Million ns)
113	 *  mult/2^shift  = ns/cyc
114	 *  mult = ns/cyc * 2^shift
115	 *  mult = 1Million/khz * 2^shift
116	 *  mult = 1000000 * 2^shift / khz
117	 *  mult = (1000000<<shift) / khz
118	 */
119	u64 tmp = ((u64)1000000) << shift_constant;
120
121	tmp += khz/2; /* round for do_div */
122	do_div(tmp, khz);
123
124	return (u32)tmp;
125}
126
127/**
128 * clocksource_hz2mult - calculates mult from hz and shift
129 * @hz:			Clocksource frequency in Hz
130 * @shift_constant:	Clocksource shift factor
131 *
132 * Helper functions that converts a hz counter
133 * frequency to a timsource multiplier, given the
134 * clocksource shift value
135 */
136static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
137{
138	/*  hz = cyc/(Billion ns)
139	 *  mult/2^shift  = ns/cyc
140	 *  mult = ns/cyc * 2^shift
141	 *  mult = 1Billion/hz * 2^shift
142	 *  mult = 1000000000 * 2^shift / hz
143	 *  mult = (1000000000<<shift) / hz
144	 */
145	u64 tmp = ((u64)1000000000) << shift_constant;
146
147	tmp += hz/2; /* round for do_div */
148	do_div(tmp, hz);
149
150	return (u32)tmp;
151}
152
153/**
154 * clocksource_read: - Access the clocksource's current cycle value
155 * @cs:		pointer to clocksource being read
156 *
157 * Uses the clocksource to return the current cycle_t value
158 */
159static inline cycle_t clocksource_read(struct clocksource *cs)
160{
161	return cs->read();
162}
163
164static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
165{
166	u64 ret = (u64)cycles;
167	ret = (ret * cs->mult) >> cs->shift;
168	return ret;
169}
170
171/**
172 * clocksource_calculate_interval - Calculates a clocksource interval struct
173 *
174 * @c:		Pointer to clocksource.
175 * @length_nsec: Desired interval length in nanoseconds.
176 *
177 * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
178 * pair and interval request.
179 *
180 * Unless you're the timekeeping code, you should not be using this!
181 */
182static inline void clocksource_calculate_interval(struct clocksource *c,
183					  	  unsigned long length_nsec)
184{
185	u64 tmp;
186
187	tmp = length_nsec;
188	tmp <<= c->shift;
189	tmp += c->mult/2;
190	do_div(tmp, c->mult);
191
192	c->cycle_interval = (cycle_t)tmp;
193	if (c->cycle_interval == 0)
194		c->cycle_interval = 1;
195
196	c->xtime_interval = (u64)c->cycle_interval * c->mult;
197}
198
199
200/* used to install a new clocksource */
201extern int clocksource_register(struct clocksource*);
202extern struct clocksource* clocksource_get_next(void);
203extern void clocksource_change_rating(struct clocksource *cs, int rating);
204extern void clocksource_resume(void);
205
206#ifdef CONFIG_GENERIC_TIME_VSYSCALL
207extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
208#else
209static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
210{
211}
212#endif
213
214#endif /* _LINUX_CLOCKSOURCE_H */
215