diff options
| -rw-r--r-- | include/linux/clockchips.h | 7 | ||||
| -rw-r--r-- | include/linux/clocksource.h | 10 | ||||
| -rw-r--r-- | kernel/time/clocksource.c | 53 |
3 files changed, 70 insertions, 0 deletions
diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h index 3b584101627..4d438b0bc10 100644 --- a/include/linux/clockchips.h +++ b/include/linux/clockchips.h @@ -130,6 +130,13 @@ extern int clockevents_program_event(struct clock_event_device *dev, extern void clockevents_handle_noop(struct clock_event_device *dev); +static inline void +clockevents_calc_mult_shift(struct clock_event_device *ce, u32 freq, u32 minsec) +{ + return clocks_calc_mult_shift(&ce->mult, &ce->shift, NSEC_PER_SEC, + freq, minsec); +} + #ifdef CONFIG_GENERIC_CLOCKEVENTS extern void clockevents_notify(unsigned long reason, void *arg); #else diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index 83d2fbd81b9..f57f8825052 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -279,6 +279,16 @@ extern void clocksource_resume(void); extern struct clocksource * __init __weak clocksource_default_clock(void); extern void clocksource_mark_unstable(struct clocksource *cs); +extern void +clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 minsec); + +static inline void +clocksource_calc_mult_shift(struct clocksource *cs, u32 freq, u32 minsec) +{ + return clocks_calc_mult_shift(&cs->mult, &cs->shift, freq, + NSEC_PER_SEC, minsec); +} + #ifdef CONFIG_GENERIC_TIME_VSYSCALL extern void update_vsyscall(struct timespec *ts, struct clocksource *c); extern void update_vsyscall_tz(void); diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 5e18c6ab2c6..407c0894ef3 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -107,6 +107,59 @@ u64 timecounter_cyc2time(struct timecounter *tc, } EXPORT_SYMBOL(timecounter_cyc2time); +/** + * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks + * @mult: pointer to mult variable + * @shift: pointer to shift variable + * @from: frequency to convert from + * @to: frequency to convert to + * @minsec: guaranteed runtime conversion range in seconds + * + * The function evaluates the shift/mult pair for the scaled math + * operations of clocksources and clockevents. + * + * @to and @from are frequency values in HZ. For clock sources @to is + * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock + * event @to is the counter frequency and @from is NSEC_PER_SEC. + * + * The @minsec conversion range argument controls the time frame in + * seconds which must be covered by the runtime conversion with the + * calculated mult and shift factors. This guarantees that no 64bit + * overflow happens when the input value of the conversion is + * multiplied with the calculated mult factor. Larger ranges may + * reduce the conversion accuracy by chosing smaller mult and shift + * factors. + */ +void +clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 minsec) +{ + u64 tmp; + u32 sft, sftacc= 32; + + /* + * Calculate the shift factor which is limiting the conversion + * range: + */ + tmp = ((u64)minsec * from) >> 32; + while (tmp) { + tmp >>=1; + sftacc--; + } + + /* + * Find the conversion shift/mult pair which has the best + * accuracy and fits the maxsec conversion range: + */ + for (sft = 32; sft > 0; sft--) { + tmp = (u64) to << sft; + do_div(tmp, from); + if ((tmp >> sftacc) == 0) + break; + } + *mult = tmp; + *shift = sft; +} + /*[Clocksource internal variables]--------- * curr_clocksource: * currently selected clocksource. |