/* linux/include/linux/clocksource.h
*
* This file contains the structure definitions for clocksources.
*
* If you are not a clocksource, or timekeeping code, you should
* not be including this file!
*/
#ifndef _LINUX_CLOCKSOURCE_H
#define _LINUX_CLOCKSOURCE_H
#include <linux/types.h>
#include <linux/timex.h>
#include <linux/time.h>
#include <linux/list.h>
#include <asm/div64.h>
#include <asm/io.h>
/* clocksource cycle base type */
typedef u64 cycle_t;
/**
* struct clocksource - hardware abstraction for a free running counter
* Provides mostly state-free accessors to the underlying hardware.
*
* @name: ptr to clocksource name
* @list: list head for registration
* @rating: rating value for selection (higher is better)
* To avoid rating inflation the following
* list should give you a guide as to how
* to assign your clocksource a rating
* 1-99: Unfit for real use
* Only available for bootup and testing purposes.
* 100-199: Base level usability.
* Functional for real use, but not desired.
* 200-299: Good.
* A correct and usable clocksource.
* 300-399: Desired.
* A reasonably fast and accurate clocksource.
* 400-499: Perfect
* The ideal clocksource. A must-use where
* available.
* @read: returns a cycle value
* @mask: bitmask for two's complement
* subtraction of non 64 bit counters
* @mult: cycle to nanosecond multiplier
* @shift: cycle to nanosecond divisor (power of two)
* @update_callback: called when safe to alter clocksource values
* @is_continuous: defines if clocksource is free-running.
* @interval_cycles: Used internally by timekeeping core, please ignore.
* @interval_snsecs: Used internally by timekeeping core, please ignore.
*/
struct clocksource {
char *name;
struct list_head list;
int rating;
cycle_t (*read)(void);
cycle_t mask;
u32 mult;
u32 shift;
int (*update_callback)(void);
int is_continuous;
/* timekeeping specific data, ignore */
cycle_t interval_cycles;
u64 interval_snsecs;
};
/**
* clocksource_khz2mult - calculates mult from khz and shift
* @khz: Clocksource frequency in KHz
* @shift_constant: Clocksource shift factor
*
* Helper functions that converts a khz counter frequency to a timsource
* multiplier, given the clocksource shift value
*/
static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
{
/* khz = cyc/(Million ns)
* mult/2^shift = ns/cyc
* mult = ns/cyc * 2^shift
* mult = 1Million/khz * 2^shift
* mult = 1000000 * 2^shift / khz
* mult = (1000000<<shift) / khz
*/
u64 tmp = ((u64)1000000) << shift_constant;
tmp += khz/2; /* round for do_div */
do_div(tmp, khz);
return (u32)tmp;
}
/**
* clocksource_hz2mult - calculates mult from hz and shift
* @hz: Clocksource frequency in Hz
* @shift_constant: Clocksource shift factor
*
* Helper functions that converts a hz counter
* frequency to a timsource multiplier, given the
* clocksource shift value
*/
static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
{
/* hz = cyc/(Billion ns)
* mult/2^shift = ns/cyc
* mult = ns/cyc * 2^shift
* mult = 1Billion/hz * 2^shift
* mult = 1000000000 * 2^shift / hz
* mult = (1000000000<<shift) / hz
*/
u64 tmp = ((u64)1000000000) << shift_constant;
tmp += hz/2; /* round for do_div */
do_div(tmp, hz);
return (u32)tmp;
}
/**
* read_clocksource: - Access the clocksource's current cycle value
* @cs: pointer to clocksource being read
*
* Uses the clocksource to return the current cycle_t value
*/
static inline cycle_t read_clocksource(struct clocksource *cs)
{
return cs->read();
}
/**
* cyc2ns - converts clocksource cycles to nanoseconds
* @cs: Pointer to clocksource
* @cycles: Cycles
*
* Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
*
* XXX - This could use some mult_lxl_ll() asm optimization
*/
static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
{
u64 ret = (u64)cycles;
ret = (ret * cs->mult) >> cs->shift;
return ret;
}
/**
* calculate_clocksource_interval - Calculates a clocksource interval struct
*
* @c: Pointer to clocksource.
* @length_nsec: Desired interval length in nanoseconds.
*
* Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
* pair and interval request.
*
* Unless you're the timekeeping code, you should not be using this!
*/
static inline void calculate_clocksource_interval(struct clocksource *c,
unsigned long length_nsec)
{
u64 tmp;
/* XXX - All of this could use a whole lot of optimization */
tmp = length_nsec;
tmp <<= c->shift;
tmp += c->mult/2;
do_div(tmp, c->mult);
c->interval_cycles = (cycle_t)tmp;
if(c->interval_cycles == 0)
c->interval_cycles = 1;
c->interval_snsecs = (u64)c->interval_cycles * c->mult;
}
/**
* error_aproximation - calculates an error adjustment for a given error
*
* @error: Error value (unsigned)
* @unit: Adjustment unit
*
* For a given error value, this function takes the adjustment unit
* and uses binary approximation to return a power of two adjustment value.
*
* This function is only for use by the the make_ntp_adj() function
* and you must hold a write on the xtime_lock when calling.
*/
static inline int error_aproximation(u64 error, u64 unit)
{
static int saved_adj = 0;
u64 adjusted_unit = unit << saved_adj;
if (error > (adjusted_unit * 2)) {
/* large error, so increment the adjustment factor */
saved_adj++;
} else if (error > adjusted_unit) {
/* just right, don't touch it */
} else if (saved_adj) {
/* small error, so drop the adjustment factor */
saved_adj--;
return 0;
}
return saved_adj;
}
/**
* make_ntp_adj - Adjusts the specified clocksource for a given error
*
* @clock: Pointer to clock to be adjusted
* @cycles_delta: Current unacounted cycle delta
* @error: Pointer to current error value
*
* Returns clock shifted nanosecond adjustment to be applied against
* the accumulated time value (ie: xtime).
*
* If the error value is large enough, this function calulates the
* (power of two) adjustment value, and adjusts the clock's mult and
* interval_snsecs values accordingly.
*
* However, since there may be some unaccumulated cycles, to avoid
* time inconsistencies we must adjust the accumulation value
* accordingly.
*
* This is not very intuitive, so the following proof should help:
* The basic timeofday algorithm: base + cycle * mult
* Thus:
* new_base + cycle * new_mult = old_base + cycle * old_mult
* new_base = old_base + cycle * old_mult - cycle * new_mult
* new_base = old_base + cycle * (old_mult - new_mult)
* new_base - old_base = cycle * (old_mult - new_mult)
* base_delta = cycle * (old_mult - new_mult)
* base_delta = cycle * (mult_delta)
*
* Where mult_delta is the adjustment value made to mult
*
*/
static inline s64 make_ntp_adj(struct clocksource *clock,
cycles_t cycles_delta, s64* error)
{
s64 ret = 0;
if (*error > ((s64)clock->interval_cycles+1)/2) {
/* calculate adjustment value */
int adjustment = error_aproximation(*error,
clock->interval_cycles);
/* adjust clock */
clock->mult += 1 << adjustment;
clock->interval_snsecs += clock->interval_cycles << adjustment;
/* adjust the base and error for the adjustment */
ret = -(cycles_delta << adjustment);
*error -= clock->interval_cycles << adjustment;
/* XXX adj error for cycle_delta offset? */
} else if ((-(*error)) > ((s64)clock->interval_cycles+1)/2) {
/* calculate adjustment value */
int adjustment = error_aproximation(-(*error),
clock->interval_cycles);
/* adjust clock */
clock->mult -= 1 << adjustment;
clock->interval_snsecs -= clock->interval_cycles << adjustment;
/* adjust the base and error for the adjustment */
ret = cycles_delta << adjustment;
*error += clock->interval_cycles << adjustment;
/* XXX adj error for cycle_delta offset? */
}
return ret;
}
/* used to install a new clocksource */
int register_clocksource(struct clocksource*);
void reselect_clocksource(void);
struct clocksource* get_next_clocksource(void);
#endif /* _LINUX_CLOCKSOURCE_H */
