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![Patrick Ohly](/assets/img/avatar_default.png)
So far struct clocksource acted as the interface between time/timekeeping.c and hardware. This patch generalizes the concept so that a similar interface can also be used in other contexts. For that it introduces new structures and related functions *without* touching the existing struct clocksource. The reasons for adding these new structures to clocksource.[ch] are * the APIs are clearly related * struct clocksource could be cleaned up to use the new structs * avoids proliferation of files with similar names (timesource.h? timecounter.h?) As outlined in the discussion with John Stultz, this patch adds * struct cyclecounter: stateless API to hardware which counts clock cycles * struct timecounter: stateful utility code built on a cyclecounter which provides a nanosecond counter * only the function to read the nanosecond counter; deltas are used internally and not exposed to users of timecounter The code does no locking of the shared state. It must be called at least as often as the cycle counter wraps around to detect these wrap arounds. Both is the responsibility of the timecounter user. Acked-by: John Stultz <johnstul@us.ibm.com> Signed-off-by: Patrick Ohly <patrick.ohly@intel.com> Signed-off-by: David S. Miller <davem@davemloft.net>
346 lines
10 KiB
C
346 lines
10 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 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
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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 (adjusted by NTP)
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* @mult_orig: cycle to nanosecond multiplier (unadjusted by NTP)
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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 mult_orig;
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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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#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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/* timekeeping specific data, ignore */
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cycle_t cycle_interval;
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u64 xtime_interval;
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u32 raw_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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struct timespec raw_time;
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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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extern struct clocksource *clock; /* current clocksource */
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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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/* Do the ns -> cycle conversion first, using original mult */
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tmp = length_nsec;
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tmp <<= c->shift;
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tmp += c->mult_orig/2;
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do_div(tmp, c->mult_orig);
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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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/* Go back from cycles -> shifted ns, this time use ntp adjused mult */
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c->xtime_interval = (u64)c->cycle_interval * c->mult;
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c->raw_interval = ((u64)c->cycle_interval * c->mult_orig) >> c->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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#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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#endif /* _LINUX_CLOCKSOURCE_H */
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