225 lines
6.0 KiB
C
225 lines
6.0 KiB
C
/* linux/include/linux/clocksource.h
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*
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* This file contains the structure definitions for clocksources.
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*
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* If you are not a clocksource, or timekeeping code, you should
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* not be including this file!
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*/
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#ifndef _LINUX_CLOCKSOURCE_H
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#define _LINUX_CLOCKSOURCE_H
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#include <linux/types.h>
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#include <linux/timex.h>
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#include <linux/time.h>
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#include <linux/list.h>
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#include <linux/cache.h>
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#include <linux/timer.h>
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#include <asm/div64.h>
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#include <asm/io.h>
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/* clocksource cycle base type */
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typedef u64 cycle_t;
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struct clocksource;
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/**
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* struct clocksource - hardware abstraction for a free running counter
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* Provides mostly state-free accessors to the underlying hardware.
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*
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* @name: ptr to clocksource name
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* @list: list head for registration
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* @rating: rating value for selection (higher is better)
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* To avoid rating inflation the following
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* list should give you a guide as to how
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* to assign your clocksource a rating
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* 1-99: Unfit for real use
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* Only available for bootup and testing purposes.
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* 100-199: Base level usability.
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* Functional for real use, but not desired.
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* 200-299: Good.
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* A correct and usable clocksource.
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* 300-399: Desired.
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* A reasonably fast and accurate clocksource.
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* 400-499: Perfect
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* The ideal clocksource. A must-use where
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* available.
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* @read: returns a cycle value
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* @mask: bitmask for two's complement
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* subtraction of non 64 bit counters
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* @mult: cycle to nanosecond multiplier
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* @shift: cycle to nanosecond divisor (power of two)
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* @flags: flags describing special properties
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* @vread: vsyscall based read
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* @resume: resume function for the clocksource, if necessary
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* @cycle_interval: Used internally by timekeeping core, please ignore.
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* @xtime_interval: Used internally by timekeeping core, please ignore.
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*/
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struct clocksource {
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/*
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* First part of structure is read mostly
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*/
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char *name;
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struct list_head list;
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int rating;
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cycle_t (*read)(void);
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cycle_t mask;
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u32 mult;
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u32 shift;
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unsigned long flags;
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cycle_t (*vread)(void);
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void (*resume)(void);
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/* timekeeping specific data, ignore */
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cycle_t cycle_interval;
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u64 xtime_interval;
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/*
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* Second part is written at each timer interrupt
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* Keep it in a different cache line to dirty no
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* more than one cache line.
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*/
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cycle_t cycle_last ____cacheline_aligned_in_smp;
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u64 xtime_nsec;
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s64 error;
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#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
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/* Watchdog related data, used by the framework */
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struct list_head wd_list;
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cycle_t wd_last;
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#endif
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};
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/*
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* Clock source flags bits::
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*/
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#define CLOCK_SOURCE_IS_CONTINUOUS 0x01
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#define CLOCK_SOURCE_MUST_VERIFY 0x02
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#define CLOCK_SOURCE_WATCHDOG 0x10
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#define CLOCK_SOURCE_VALID_FOR_HRES 0x20
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/* simplify initialization of mask field */
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#define CLOCKSOURCE_MASK(bits) (cycle_t)(bits<64 ? ((1ULL<<bits)-1) : -1)
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/**
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* clocksource_khz2mult - calculates mult from khz and shift
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* @khz: Clocksource frequency in KHz
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* @shift_constant: Clocksource shift factor
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*
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* Helper functions that converts a khz counter frequency to a timsource
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* multiplier, given the clocksource shift value
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*/
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static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
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{
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/* khz = cyc/(Million ns)
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* mult/2^shift = ns/cyc
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* mult = ns/cyc * 2^shift
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* mult = 1Million/khz * 2^shift
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* mult = 1000000 * 2^shift / khz
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* mult = (1000000<<shift) / khz
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*/
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u64 tmp = ((u64)1000000) << shift_constant;
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tmp += khz/2; /* round for do_div */
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do_div(tmp, khz);
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return (u32)tmp;
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}
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/**
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* clocksource_hz2mult - calculates mult from hz and shift
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* @hz: Clocksource frequency in Hz
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* @shift_constant: Clocksource shift factor
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*
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* Helper functions that converts a hz counter
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* frequency to a timsource multiplier, given the
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* clocksource shift value
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*/
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static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
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{
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/* hz = cyc/(Billion ns)
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* mult/2^shift = ns/cyc
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* mult = ns/cyc * 2^shift
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* mult = 1Billion/hz * 2^shift
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* mult = 1000000000 * 2^shift / hz
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* mult = (1000000000<<shift) / hz
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*/
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u64 tmp = ((u64)1000000000) << shift_constant;
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tmp += hz/2; /* round for do_div */
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do_div(tmp, hz);
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return (u32)tmp;
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}
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/**
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* clocksource_read: - Access the clocksource's current cycle value
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* @cs: pointer to clocksource being read
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*
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* Uses the clocksource to return the current cycle_t value
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*/
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static inline cycle_t clocksource_read(struct clocksource *cs)
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{
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return cs->read();
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}
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/**
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* cyc2ns - converts clocksource cycles to nanoseconds
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* @cs: Pointer to clocksource
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* @cycles: Cycles
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*
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* Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
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*
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* XXX - This could use some mult_lxl_ll() asm optimization
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*/
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static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
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{
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u64 ret = (u64)cycles;
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ret = (ret * cs->mult) >> cs->shift;
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return ret;
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}
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/**
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* clocksource_calculate_interval - Calculates a clocksource interval struct
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*
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* @c: Pointer to clocksource.
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* @length_nsec: Desired interval length in nanoseconds.
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*
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* Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
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* pair and interval request.
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*
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* Unless you're the timekeeping code, you should not be using this!
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*/
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static inline void clocksource_calculate_interval(struct clocksource *c,
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unsigned long length_nsec)
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{
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u64 tmp;
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/* XXX - All of this could use a whole lot of optimization */
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tmp = length_nsec;
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tmp <<= c->shift;
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tmp += c->mult/2;
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do_div(tmp, c->mult);
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c->cycle_interval = (cycle_t)tmp;
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if (c->cycle_interval == 0)
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c->cycle_interval = 1;
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c->xtime_interval = (u64)c->cycle_interval * c->mult;
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}
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/* used to install a new clocksource */
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extern int clocksource_register(struct clocksource*);
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extern struct clocksource* clocksource_get_next(void);
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extern void clocksource_change_rating(struct clocksource *cs, int rating);
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extern void clocksource_resume(void);
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#ifdef CONFIG_GENERIC_TIME_VSYSCALL
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extern void update_vsyscall(struct timespec *ts, struct clocksource *c);
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#else
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static inline void update_vsyscall(struct timespec *ts, struct clocksource *c)
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{
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}
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#endif
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#endif /* _LINUX_CLOCKSOURCE_H */
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