diff options
| -rw-r--r-- | common/clock.c | 55 | ||||
| -rw-r--r-- | include/clock.h | 2 |
2 files changed, 57 insertions, 0 deletions
diff --git a/common/clock.c b/common/clock.c index 15df0abb48..79c06c8ddc 100644 --- a/common/clock.c +++ b/common/clock.c @@ -57,6 +57,61 @@ uint64_t get_time_ns(void) EXPORT_SYMBOL(get_time_ns); /** + * 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 + * @maxsec: 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 @maxsec 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(uint32_t *mult, uint32_t *shift, uint32_t from, uint32_t to, uint32_t maxsec) +{ + uint64_t tmp; + uint32_t sft, sftacc = 32; + + /* + * Calculate the shift factor which is limiting the conversion + * range: + */ + tmp = ((uint64_t)maxsec * 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 = (uint64_t) to << sft; + tmp += from / 2; + do_div(tmp, from); + if ((tmp >> sftacc) == 0) + break; + } + *mult = tmp; + *shift = sft; +} + + +/** * clocksource_hz2mult - calculates mult from hz and shift * @hz: Clocksource frequency in Hz * @shift_constant: Clocksource shift factor diff --git a/include/clock.h b/include/clock.h index b9acdb9b69..af5b9395bd 100644 --- a/include/clock.h +++ b/include/clock.h @@ -25,6 +25,8 @@ int init_clock(struct clocksource *); uint64_t get_time_ns(void); +void clocks_calc_mult_shift(uint32_t *mult, uint32_t *shift, uint32_t from, uint32_t to, uint32_t maxsec); + uint32_t clocksource_hz2mult(uint32_t hz, uint32_t shift_constant); int is_timeout(uint64_t start_ns, uint64_t time_offset_ns); |