diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/timecounter.h | 31 |
1 files changed, 29 insertions, 2 deletions
diff --git a/include/linux/timecounter.h b/include/linux/timecounter.h index dce03a5cafb7..7de6b350e559 100644 --- a/include/linux/timecounter.h +++ b/include/linux/timecounter.h @@ -115,6 +115,15 @@ extern void timecounter_init(struct timecounter *tc, */ extern u64 timecounter_read(struct timecounter *tc); +/* + * This is like cyclecounter_cyc2ns(), but it is used for computing a + * time previous to the time stored in the cycle counter. + */ +static inline u64 cc_cyc2ns_backwards(const struct cyclecounter *cc, u64 cycles, u64 frac) +{ + return ((cycles * cc->mult) - frac) >> cc->shift; +} + /** * timecounter_cyc2time - convert a cycle counter to same * time base as values returned by @@ -131,7 +140,25 @@ extern u64 timecounter_read(struct timecounter *tc); * * Returns: cycle counter converted to nanoseconds since the initial time stamp */ -extern u64 timecounter_cyc2time(const struct timecounter *tc, - u64 cycle_tstamp); +static inline u64 timecounter_cyc2time(const struct timecounter *tc, u64 cycle_tstamp) +{ + const struct cyclecounter *cc = tc->cc; + u64 delta = (cycle_tstamp - tc->cycle_last) & cc->mask; + u64 nsec = tc->nsec, frac = tc->frac; + + /* + * Instead of always treating cycle_tstamp as more recent than + * tc->cycle_last, detect when it is too far in the future and + * treat it as old time stamp instead. + */ + if (unlikely(delta > cc->mask / 2)) { + delta = (tc->cycle_last - cycle_tstamp) & cc->mask; + nsec -= cc_cyc2ns_backwards(cc, delta, frac); + } else { + nsec += cyclecounter_cyc2ns(cc, delta, tc->mask, &frac); + } + + return nsec; +} #endif |