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linux-next/include/linux/timex.h
Paul Mackerras 726c14bf49 [PATCH] Provide an interface for getting the current tick length 
This provides an interface for arch code to find out how many
nanoseconds are going to be added on to xtime by the next call to
do_timer.  The value returned is a fixed-point number in 52.12 format
in nanoseconds.  The reason for this format is that it gives the
full precision that the timekeeping code is using internally.

The motivation for this is to fix a problem that has arisen on 32-bit
powerpc in that the value returned by do_gettimeofday drifts apart
from xtime if NTP is being used.  PowerPC is now using a lockless
do_gettimeofday based on reading the timebase register and performing
some simple arithmetic.  (This method of getting the time is also
exported to userspace via the VDSO.)  However, the factor and offset
it uses were calculated based on the nominal tick length and weren't
being adjusted when NTP varied the tick length.

Note that 64-bit powerpc has had the lockless do_gettimeofday for a
long time now.  It also had an extremely hairy routine that got called
from the 32-bit compat routine for adjtimex, which adjusted the
factor and offset according to what it thought the timekeeping code
was going to do.  Not only was this only called if a 32-bit task did
adjtimex (i.e. not if a 64-bit task did adjtimex), it was also
duplicating computations from kernel/timer.c and it wasn't clear that
it was (still) correct.

The simple solution is to ask the timekeeping code how long the
current jiffy will be on each timer interrupt, after calling
do_timer.  If this jiffy will be a different length from the last one,
we then need to compute new values for the factor and offset used in
the lockless do_gettimeofday.  In this way we can keep xtime and
do_gettimeofday in sync, even when NTP is varying the tick length.

Note that when adjtimex varies the tick length, it almost always
introduces the variation from the next tick on.  The only case I could
see where adjtimex would vary the length of the current tick is when
an old-style adjtime adjustment is being cancelled.  (It's not clear
to me why the adjustment has to be cancelled immediately rather than
from the next tick on.)  Thus I don't see any real need for a hook in
adjtimex; the rare case of an old-style adjustment being cancelled can
be fixed up at the next tick.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: john stultz <johnstul@us.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-02-17 08:24:29 -08:00

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/*****************************************************************************
* *
* Copyright (c) David L. Mills 1993 *
* *
* Permission to use, copy, modify, and distribute this software and its *
* documentation for any purpose and without fee is hereby granted, provided *
* that the above copyright notice appears in all copies and that both the *
* copyright notice and this permission notice appear in supporting *
* documentation, and that the name University of Delaware not be used in *
* advertising or publicity pertaining to distribution of the software *
* without specific, written prior permission. The University of Delaware *
* makes no representations about the suitability this software for any *
* purpose. It is provided "as is" without express or implied warranty. *
* *
*****************************************************************************/
/*
* Modification history timex.h
*
* 29 Dec 97 Russell King
* Moved CLOCK_TICK_RATE, CLOCK_TICK_FACTOR and FINETUNE to asm/timex.h
* for ARM machines
*
* 9 Jan 97 Adrian Sun
* Shifted LATCH define to allow access to alpha machines.
*
* 26 Sep 94 David L. Mills
* Added defines for hybrid phase/frequency-lock loop.
*
* 19 Mar 94 David L. Mills
* Moved defines from kernel routines to header file and added new
* defines for PPS phase-lock loop.
*
* 20 Feb 94 David L. Mills
* Revised status codes and structures for external clock and PPS
* signal discipline.
*
* 28 Nov 93 David L. Mills
* Adjusted parameters to improve stability and increase poll
* interval.
*
* 17 Sep 93 David L. Mills
* Created file $NTP/include/sys/timex.h
* 07 Oct 93 Torsten Duwe
* Derived linux/timex.h
* 1995-08-13 Torsten Duwe
* kernel PLL updated to 1994-12-13 specs (rfc-1589)
* 1997-08-30 Ulrich Windl
* Added new constant NTP_PHASE_LIMIT
* 2004-08-12 Christoph Lameter
* Reworked time interpolation logic
*/
#ifndef _LINUX_TIMEX_H
#define _LINUX_TIMEX_H
#include <linux/config.h>
#include <linux/compiler.h>
#include <linux/time.h>
#include <asm/param.h>
#include <asm/timex.h>
/*
* SHIFT_KG and SHIFT_KF establish the damping of the PLL and are chosen
* for a slightly underdamped convergence characteristic. SHIFT_KH
* establishes the damping of the FLL and is chosen by wisdom and black
* art.
*
* MAXTC establishes the maximum time constant of the PLL. With the
* SHIFT_KG and SHIFT_KF values given and a time constant range from
* zero to MAXTC, the PLL will converge in 15 minutes to 16 hours,
* respectively.
*/
#define SHIFT_KG 6 /* phase factor (shift) */
#define SHIFT_KF 16 /* PLL frequency factor (shift) */
#define SHIFT_KH 2 /* FLL frequency factor (shift) */
#define MAXTC 6 /* maximum time constant (shift) */
/*
* The SHIFT_SCALE define establishes the decimal point of the time_phase
* variable which serves as an extension to the low-order bits of the
* system clock variable. The SHIFT_UPDATE define establishes the decimal
* point of the time_offset variable which represents the current offset
* with respect to standard time. The FINENSEC define represents 1 nsec in
* scaled units.
*
* SHIFT_USEC defines the scaling (shift) of the time_freq and
* time_tolerance variables, which represent the current frequency
* offset and maximum frequency tolerance.
*
* FINENSEC is 1 ns in SHIFT_UPDATE units of the time_phase variable.
*/
#define SHIFT_SCALE 22 /* phase scale (shift) */
#define SHIFT_UPDATE (SHIFT_KG + MAXTC) /* time offset scale (shift) */
#define SHIFT_USEC 16 /* frequency offset scale (shift) */
#define FINENSEC (1L << (SHIFT_SCALE - 10)) /* ~1 ns in phase units */
#define MAXPHASE 512000L /* max phase error (us) */
#define MAXFREQ (512L << SHIFT_USEC) /* max frequency error (ppm) */
#define MAXTIME (200L << PPS_AVG) /* max PPS error (jitter) (200 us) */
#define MINSEC 16L /* min interval between updates (s) */
#define MAXSEC 1200L /* max interval between updates (s) */
#define NTP_PHASE_LIMIT (MAXPHASE << 5) /* beyond max. dispersion */
/*
* The following defines are used only if a pulse-per-second (PPS)
* signal is available and connected via a modem control lead, such as
* produced by the optional ppsclock feature incorporated in the Sun
* asynch driver. They establish the design parameters of the frequency-
* lock loop used to discipline the CPU clock oscillator to the PPS
* signal.
*
* PPS_AVG is the averaging factor for the frequency loop, as well as
* the time and frequency dispersion.
*
* PPS_SHIFT and PPS_SHIFTMAX specify the minimum and maximum
* calibration intervals, respectively, in seconds as a power of two.
*
* PPS_VALID is the maximum interval before the PPS signal is considered
* invalid and protocol updates used directly instead.
*
* MAXGLITCH is the maximum interval before a time offset of more than
* MAXTIME is believed.
*/
#define PPS_AVG 2 /* pps averaging constant (shift) */
#define PPS_SHIFT 2 /* min interval duration (s) (shift) */
#define PPS_SHIFTMAX 8 /* max interval duration (s) (shift) */
#define PPS_VALID 120 /* pps signal watchdog max (s) */
#define MAXGLITCH 30 /* pps signal glitch max (s) */
/*
* syscall interface - used (mainly by NTP daemon)
* to discipline kernel clock oscillator
*/
struct timex {
unsigned int modes; /* mode selector */
long offset; /* time offset (usec) */
long freq; /* frequency offset (scaled ppm) */
long maxerror; /* maximum error (usec) */
long esterror; /* estimated error (usec) */
int status; /* clock command/status */
long constant; /* pll time constant */
long precision; /* clock precision (usec) (read only) */
long tolerance; /* clock frequency tolerance (ppm)
* (read only)
*/
struct timeval time; /* (read only) */
long tick; /* (modified) usecs between clock ticks */
long ppsfreq; /* pps frequency (scaled ppm) (ro) */
long jitter; /* pps jitter (us) (ro) */
int shift; /* interval duration (s) (shift) (ro) */
long stabil; /* pps stability (scaled ppm) (ro) */
long jitcnt; /* jitter limit exceeded (ro) */
long calcnt; /* calibration intervals (ro) */
long errcnt; /* calibration errors (ro) */
long stbcnt; /* stability limit exceeded (ro) */
int :32; int :32; int :32; int :32;
int :32; int :32; int :32; int :32;
int :32; int :32; int :32; int :32;
};
/*
* Mode codes (timex.mode)
*/
#define ADJ_OFFSET 0x0001 /* time offset */
#define ADJ_FREQUENCY 0x0002 /* frequency offset */
#define ADJ_MAXERROR 0x0004 /* maximum time error */
#define ADJ_ESTERROR 0x0008 /* estimated time error */
#define ADJ_STATUS 0x0010 /* clock status */
#define ADJ_TIMECONST 0x0020 /* pll time constant */
#define ADJ_TICK 0x4000 /* tick value */
#define ADJ_OFFSET_SINGLESHOT 0x8001 /* old-fashioned adjtime */
/* xntp 3.4 compatibility names */
#define MOD_OFFSET ADJ_OFFSET
#define MOD_FREQUENCY ADJ_FREQUENCY
#define MOD_MAXERROR ADJ_MAXERROR
#define MOD_ESTERROR ADJ_ESTERROR
#define MOD_STATUS ADJ_STATUS
#define MOD_TIMECONST ADJ_TIMECONST
#define MOD_CLKB ADJ_TICK
#define MOD_CLKA ADJ_OFFSET_SINGLESHOT /* 0x8000 in original */
/*
* Status codes (timex.status)
*/
#define STA_PLL 0x0001 /* enable PLL updates (rw) */
#define STA_PPSFREQ 0x0002 /* enable PPS freq discipline (rw) */
#define STA_PPSTIME 0x0004 /* enable PPS time discipline (rw) */
#define STA_FLL 0x0008 /* select frequency-lock mode (rw) */
#define STA_INS 0x0010 /* insert leap (rw) */
#define STA_DEL 0x0020 /* delete leap (rw) */
#define STA_UNSYNC 0x0040 /* clock unsynchronized (rw) */
#define STA_FREQHOLD 0x0080 /* hold frequency (rw) */
#define STA_PPSSIGNAL 0x0100 /* PPS signal present (ro) */
#define STA_PPSJITTER 0x0200 /* PPS signal jitter exceeded (ro) */
#define STA_PPSWANDER 0x0400 /* PPS signal wander exceeded (ro) */
#define STA_PPSERROR 0x0800 /* PPS signal calibration error (ro) */
#define STA_CLOCKERR 0x1000 /* clock hardware fault (ro) */
#define STA_RONLY (STA_PPSSIGNAL | STA_PPSJITTER | STA_PPSWANDER | \
STA_PPSERROR | STA_CLOCKERR) /* read-only bits */
/*
* Clock states (time_state)
*/
#define TIME_OK 0 /* clock synchronized, no leap second */
#define TIME_INS 1 /* insert leap second */
#define TIME_DEL 2 /* delete leap second */
#define TIME_OOP 3 /* leap second in progress */
#define TIME_WAIT 4 /* leap second has occurred */
#define TIME_ERROR 5 /* clock not synchronized */
#define TIME_BAD TIME_ERROR /* bw compat */
#ifdef __KERNEL__
/*
* kernel variables
* Note: maximum error = NTP synch distance = dispersion + delay / 2;
* estimated error = NTP dispersion.
*/
extern unsigned long tick_usec; /* USER_HZ period (usec) */
extern unsigned long tick_nsec; /* ACTHZ period (nsec) */
extern int tickadj; /* amount of adjustment per tick */
/*
* phase-lock loop variables
*/
extern int time_state; /* clock status */
extern int time_status; /* clock synchronization status bits */
extern long time_offset; /* time adjustment (us) */
extern long time_constant; /* pll time constant */
extern long time_tolerance; /* frequency tolerance (ppm) */
extern long time_precision; /* clock precision (us) */
extern long time_maxerror; /* maximum error */
extern long time_esterror; /* estimated error */
extern long time_freq; /* frequency offset (scaled ppm) */
extern long time_reftime; /* time at last adjustment (s) */
extern long time_adjust; /* The amount of adjtime left */
extern long time_next_adjust; /* Value for time_adjust at next tick */
/* interface variables pps->timer interrupt */
extern long pps_offset; /* pps time offset (us) */
extern long pps_jitter; /* time dispersion (jitter) (us) */
extern long pps_freq; /* frequency offset (scaled ppm) */
extern long pps_stabil; /* frequency dispersion (scaled ppm) */
extern long pps_valid; /* pps signal watchdog counter */
/* interface variables pps->adjtimex */
extern int pps_shift; /* interval duration (s) (shift) */
extern long pps_jitcnt; /* jitter limit exceeded */
extern long pps_calcnt; /* calibration intervals */
extern long pps_errcnt; /* calibration errors */
extern long pps_stbcnt; /* stability limit exceeded */
/**
* ntp_clear - Clears the NTP state variables
*
* Must be called while holding a write on the xtime_lock
*/
static inline void ntp_clear(void)
{
time_adjust = 0; /* stop active adjtime() */
time_status |= STA_UNSYNC;
time_maxerror = NTP_PHASE_LIMIT;
time_esterror = NTP_PHASE_LIMIT;
}
/**
* ntp_synced - Returns 1 if the NTP status is not UNSYNC
*
*/
static inline int ntp_synced(void)
{
return !(time_status & STA_UNSYNC);
}
/* Required to safely shift negative values */
#define shift_right(x, s) ({ \
__typeof__(x) __x = (x); \
__typeof__(s) __s = (s); \
__x < 0 ? -(-__x >> __s) : __x >> __s; \
})
#ifdef CONFIG_TIME_INTERPOLATION
#define TIME_SOURCE_CPU 0
#define TIME_SOURCE_MMIO64 1
#define TIME_SOURCE_MMIO32 2
#define TIME_SOURCE_FUNCTION 3
/* For proper operations time_interpolator clocks must run slightly slower
* than the standard clock since the interpolator may only correct by having
* time jump forward during a tick. A slower clock is usually a side effect
* of the integer divide of the nanoseconds in a second by the frequency.
* The accuracy of the division can be increased by specifying a shift.
* However, this may cause the clock not to be slow enough.
* The interpolator will self-tune the clock by slowing down if no
* resets occur or speeding up if the time jumps per analysis cycle
* become too high.
*
* Setting jitter compensates for a fluctuating timesource by comparing
* to the last value read from the timesource to insure that an earlier value
* is not returned by a later call. The price to pay
* for the compensation is that the timer routines are not as scalable anymore.
*/
struct time_interpolator {
u16 source; /* time source flags */
u8 shift; /* increases accuracy of multiply by shifting. */
/* Note that bits may be lost if shift is set too high */
u8 jitter; /* if set compensate for fluctuations */
u32 nsec_per_cyc; /* set by register_time_interpolator() */
void *addr; /* address of counter or function */
u64 mask; /* mask the valid bits of the counter */
unsigned long offset; /* nsec offset at last update of interpolator */
u64 last_counter; /* counter value in units of the counter at last update */
u64 last_cycle; /* Last timer value if TIME_SOURCE_JITTER is set */
u64 frequency; /* frequency in counts/second */
long drift; /* drift in parts-per-million (or -1) */
unsigned long skips; /* skips forward */
unsigned long ns_skipped; /* nanoseconds skipped */
struct time_interpolator *next;
};
extern void register_time_interpolator(struct time_interpolator *);
extern void unregister_time_interpolator(struct time_interpolator *);
extern void time_interpolator_reset(void);
extern unsigned long time_interpolator_get_offset(void);
#else /* !CONFIG_TIME_INTERPOLATION */
static inline void
time_interpolator_reset(void)
{
}
#endif /* !CONFIG_TIME_INTERPOLATION */
/* Returns how long ticks are at present, in ns / 2^(SHIFT_SCALE-10). */
extern u64 current_tick_length(void);
#endif /* KERNEL */
#endif /* LINUX_TIMEX_H */
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