7f9f303aa3
Add a CLOCKSOURCE_MASK macro to simplify initializing the mask for a struct clocksource, and use it to replace literal mask constants in the various clocksource drivers. Signed-off-by: Jim Cromie <jim.cromie@gmail.com> Acked-by: John Stultz <johnstul@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
280 lines
8.1 KiB
C
280 lines
8.1 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 <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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/**
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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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* @update_callback: called when safe to alter clocksource values
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* @is_continuous: defines if clocksource is free-running.
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* @interval_cycles: Used internally by timekeeping core, please ignore.
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* @interval_snsecs: Used internally by timekeeping core, please ignore.
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*/
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struct clocksource {
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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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int (*update_callback)(void);
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int is_continuous;
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/* timekeeping specific data, ignore */
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cycle_t interval_cycles;
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u64 interval_snsecs;
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};
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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->interval_cycles = (cycle_t)tmp;
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if(c->interval_cycles == 0)
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c->interval_cycles = 1;
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c->interval_snsecs = (u64)c->interval_cycles * c->mult;
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}
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/**
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* error_aproximation - calculates an error adjustment for a given error
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*
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* @error: Error value (unsigned)
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* @unit: Adjustment unit
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*
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* For a given error value, this function takes the adjustment unit
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* and uses binary approximation to return a power of two adjustment value.
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*
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* This function is only for use by the the make_ntp_adj() function
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* and you must hold a write on the xtime_lock when calling.
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*/
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static inline int error_aproximation(u64 error, u64 unit)
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{
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static int saved_adj = 0;
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u64 adjusted_unit = unit << saved_adj;
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if (error > (adjusted_unit * 2)) {
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/* large error, so increment the adjustment factor */
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saved_adj++;
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} else if (error > adjusted_unit) {
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/* just right, don't touch it */
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} else if (saved_adj) {
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/* small error, so drop the adjustment factor */
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saved_adj--;
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return 0;
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}
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return saved_adj;
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}
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/**
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* make_ntp_adj - Adjusts the specified clocksource for a given error
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*
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* @clock: Pointer to clock to be adjusted
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* @cycles_delta: Current unacounted cycle delta
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* @error: Pointer to current error value
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*
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* Returns clock shifted nanosecond adjustment to be applied against
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* the accumulated time value (ie: xtime).
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*
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* If the error value is large enough, this function calulates the
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* (power of two) adjustment value, and adjusts the clock's mult and
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* interval_snsecs values accordingly.
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*
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* However, since there may be some unaccumulated cycles, to avoid
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* time inconsistencies we must adjust the accumulation value
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* accordingly.
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*
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* This is not very intuitive, so the following proof should help:
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* The basic timeofday algorithm: base + cycle * mult
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* Thus:
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* new_base + cycle * new_mult = old_base + cycle * old_mult
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* new_base = old_base + cycle * old_mult - cycle * new_mult
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* new_base = old_base + cycle * (old_mult - new_mult)
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* new_base - old_base = cycle * (old_mult - new_mult)
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* base_delta = cycle * (old_mult - new_mult)
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* base_delta = cycle * (mult_delta)
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*
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* Where mult_delta is the adjustment value made to mult
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*
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*/
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static inline s64 make_ntp_adj(struct clocksource *clock,
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cycles_t cycles_delta, s64* error)
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{
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s64 ret = 0;
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if (*error > ((s64)clock->interval_cycles+1)/2) {
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/* calculate adjustment value */
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int adjustment = error_aproximation(*error,
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clock->interval_cycles);
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/* adjust clock */
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clock->mult += 1 << adjustment;
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clock->interval_snsecs += clock->interval_cycles << adjustment;
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/* adjust the base and error for the adjustment */
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ret = -(cycles_delta << adjustment);
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*error -= clock->interval_cycles << adjustment;
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/* XXX adj error for cycle_delta offset? */
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} else if ((-(*error)) > ((s64)clock->interval_cycles+1)/2) {
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/* calculate adjustment value */
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int adjustment = error_aproximation(-(*error),
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clock->interval_cycles);
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/* adjust clock */
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clock->mult -= 1 << adjustment;
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clock->interval_snsecs -= clock->interval_cycles << adjustment;
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/* adjust the base and error for the adjustment */
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ret = cycles_delta << adjustment;
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*error += clock->interval_cycles << adjustment;
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/* XXX adj error for cycle_delta offset? */
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}
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return ret;
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}
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/* used to install a new clocksource */
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int clocksource_register(struct clocksource*);
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void clocksource_reselect(void);
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struct clocksource* clocksource_get_next(void);
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#endif /* _LINUX_CLOCKSOURCE_H */
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