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time: Add cycles to nanoseconds translation 

The timekeeping code does not currently provide a way to translate
externally provided clocksource cycles to system time. The cycle count
is always provided by the result clocksource read() method internal to
the timekeeping code. The added function timekeeping_cycles_to_ns()
calculated a nanosecond value from a cycle count that can be added to
tk_read_base.base value yielding the current system time. This allows
clocksource cycle values external to the timekeeping code to provide a
cycle count that can be transformed to system time.

Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: kevin.b.stanton@intel.com
Cc: kevin.j.clarke@intel.com
Cc: hpa@zytor.com
Cc: jeffrey.t.kirsher@intel.com
Cc: netdev@vger.kernel.org
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Christopher S. Hall <christopher.s.hall@intel.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
This commit is contained in:
Christopher S. Hall 2016-02-22 03:15:19 -08:00 committed by John Stultz
parent 232d26373d
commit 6bd58f09e1
1 changed files with 22 additions and 5 deletions
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27
kernel/time/timekeeping.c
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@ -298,19 +298,36 @@ u32 (*arch_gettimeoffset)(void) = default_arch_gettimeoffset;
static inline u32 arch_gettimeoffset(void) { return 0; }
#endif
static inline s64 timekeeping_get_ns(struct tk_read_base *tkr)
static inline s64 timekeeping_delta_to_ns(struct tk_read_base *tkr,
cycle_t delta)
{
cycle_t delta;
s64 nsec;
delta = timekeeping_get_delta(tkr);
nsec = (delta * tkr->mult + tkr->xtime_nsec) >> tkr->shift;
nsec = delta * tkr->mult + tkr->xtime_nsec;
nsec >>= tkr->shift;
/* If arch requires, add in get_arch_timeoffset() */
return nsec + arch_gettimeoffset();
}
static inline s64 timekeeping_get_ns(struct tk_read_base *tkr)
{
cycle_t delta;
delta = timekeeping_get_delta(tkr);
return timekeeping_delta_to_ns(tkr, delta);
}
static inline s64 timekeeping_cycles_to_ns(struct tk_read_base *tkr,
cycle_t cycles)
{
cycle_t delta;
/* calculate the delta since the last update_wall_time */
delta = clocksource_delta(cycles, tkr->cycle_last, tkr->mask);
return timekeeping_delta_to_ns(tkr, delta);
}
/**
* update_fast_timekeeper - Update the fast and NMI safe monotonic timekeeper.
* @tkr: Timekeeping readout base from which we take the update