300 lines
9.1 KiB
C
300 lines
9.1 KiB
C
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/* 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 <linux/init.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 cyclecounter - hardware abstraction for a free running counter
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* Provides completely state-free accessors to the underlying hardware.
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* Depending on which hardware it reads, the cycle counter may wrap
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* around quickly. Locking rules (if necessary) have to be defined
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* by the implementor and user of specific instances of this API.
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*
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* @read: returns the current 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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* see CLOCKSOURCE_MASK() helper macro
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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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*/
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struct cyclecounter {
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cycle_t (*read)(const struct cyclecounter *cc);
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cycle_t mask;
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u32 mult;
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u32 shift;
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};
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/**
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* struct timecounter - layer above a %struct cyclecounter which counts nanoseconds
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* Contains the state needed by timecounter_read() to detect
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* cycle counter wrap around. Initialize with
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* timecounter_init(). Also used to convert cycle counts into the
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* corresponding nanosecond counts with timecounter_cyc2time(). Users
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* of this code are responsible for initializing the underlying
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* cycle counter hardware, locking issues and reading the time
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* more often than the cycle counter wraps around. The nanosecond
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* counter will only wrap around after ~585 years.
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*
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* @cc: the cycle counter used by this instance
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* @cycle_last: most recent cycle counter value seen by
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* timecounter_read()
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* @nsec: continuously increasing count
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*/
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struct timecounter {
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const struct cyclecounter *cc;
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cycle_t cycle_last;
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u64 nsec;
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};
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/**
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* cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
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* @tc: Pointer to cycle counter.
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* @cycles: Cycles
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*
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* XXX - This could use some mult_lxl_ll() asm optimization. Same code
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* as in cyc2ns, but with unsigned result.
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*/
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static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
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cycle_t cycles)
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{
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u64 ret = (u64)cycles;
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ret = (ret * cc->mult) >> cc->shift;
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return ret;
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}
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/**
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* timecounter_init - initialize a time counter
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* @tc: Pointer to time counter which is to be initialized/reset
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* @cc: A cycle counter, ready to be used.
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* @start_tstamp: Arbitrary initial time stamp.
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*
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* After this call the current cycle register (roughly) corresponds to
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* the initial time stamp. Every call to timecounter_read() increments
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* the time stamp counter by the number of elapsed nanoseconds.
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*/
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extern void timecounter_init(struct timecounter *tc,
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const struct cyclecounter *cc,
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u64 start_tstamp);
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/**
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* timecounter_read - return nanoseconds elapsed since timecounter_init()
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* plus the initial time stamp
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* @tc: Pointer to time counter.
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*
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* In other words, keeps track of time since the same epoch as
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* the function which generated the initial time stamp.
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*/
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extern u64 timecounter_read(struct timecounter *tc);
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/**
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* timecounter_cyc2time - convert a cycle counter to same
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* time base as values returned by
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* timecounter_read()
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* @tc: Pointer to time counter.
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* @cycle: a value returned by tc->cc->read()
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*
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* Cycle counts that are converted correctly as long as they
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* fall into the interval [-1/2 max cycle count, +1/2 max cycle count],
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* with "max cycle count" == cs->mask+1.
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*
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* This allows conversion of cycle counter values which were generated
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* in the past.
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*/
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extern u64 timecounter_cyc2time(struct timecounter *tc,
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cycle_t cycle_tstamp);
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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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* This is the structure used for system time.
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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, passes clocksource as argument
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* @enable: optional function to enable the clocksource
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* @disable: optional function to disable the clocksource
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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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* @max_idle_ns: max idle time permitted by the clocksource (nsecs)
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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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*/
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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)(struct clocksource *cs);
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int (*enable)(struct clocksource *cs);
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void (*disable)(struct clocksource *cs);
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cycle_t mask;
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u32 mult;
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u32 shift;
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u64 max_idle_ns;
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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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#ifdef CONFIG_IA64
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void *fsys_mmio; /* used by fsyscall asm code */
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#define CLKSRC_FSYS_MMIO_SET(mmio, addr) ((mmio) = (addr))
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#else
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#define CLKSRC_FSYS_MMIO_SET(mmio, addr) do { } while (0)
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#endif
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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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#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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#define CLOCK_SOURCE_UNSTABLE 0x40
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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_cyc2ns - converts clocksource cycles to nanoseconds
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*
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* Converts cycles to nanoseconds, using the given mult and shift.
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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 clocksource_cyc2ns(cycle_t cycles, u32 mult, u32 shift)
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{
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return ((u64) cycles * mult) >> shift;
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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 void clocksource_unregister(struct clocksource*);
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extern void clocksource_touch_watchdog(void);
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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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extern struct clocksource * __init __weak clocksource_default_clock(void);
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extern void clocksource_mark_unstable(struct clocksource *cs);
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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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extern void update_vsyscall_tz(void);
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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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static inline void update_vsyscall_tz(void)
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{
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}
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#endif
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extern void timekeeping_notify(struct clocksource *clock);
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#endif /* _LINUX_CLOCKSOURCE_H */
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