diff options
Diffstat (limited to 'kernel/time/clocksource.c')
| -rw-r--r-- | kernel/time/clocksource.c | 53 |
1 files changed, 27 insertions, 26 deletions
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index c18d7efa1b4..d9d5f8c885f 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -113,7 +113,7 @@ EXPORT_SYMBOL_GPL(timecounter_cyc2time); * @shift: pointer to shift variable * @from: frequency to convert from * @to: frequency to convert to - * @minsec: guaranteed runtime conversion range in seconds + * @maxsec: guaranteed runtime conversion range in seconds * * The function evaluates the shift/mult pair for the scaled math * operations of clocksources and clockevents. @@ -122,7 +122,7 @@ EXPORT_SYMBOL_GPL(timecounter_cyc2time); * 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 + * 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 @@ -131,7 +131,7 @@ EXPORT_SYMBOL_GPL(timecounter_cyc2time); * factors. */ void -clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 minsec) +clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 maxsec) { u64 tmp; u32 sft, sftacc= 32; @@ -140,7 +140,7 @@ clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 minsec) * Calculate the shift factor which is limiting the conversion * range: */ - tmp = ((u64)minsec * from) >> 32; + tmp = ((u64)maxsec * from) >> 32; while (tmp) { tmp >>=1; sftacc--; @@ -152,6 +152,7 @@ clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 minsec) */ for (sft = 32; sft > 0; sft--) { tmp = (u64) to << sft; + tmp += from / 2; do_div(tmp, from); if ((tmp >> sftacc) == 0) break; @@ -625,19 +626,6 @@ static void clocksource_enqueue(struct clocksource *cs) list_add(&cs->list, entry); } - -/* - * Maximum time we expect to go between ticks. This includes idle - * tickless time. It provides the trade off between selecting a - * mult/shift pair that is very precise but can only handle a short - * period of time, vs. a mult/shift pair that can handle long periods - * of time but isn't as precise. - * - * This is a subsystem constant, and actual hardware limitations - * may override it (ie: clocksources that wrap every 3 seconds). - */ -#define MAX_UPDATE_LENGTH 5 /* Seconds */ - /** * __clocksource_updatefreq_scale - Used update clocksource with new freq * @t: clocksource to be registered @@ -651,15 +639,28 @@ static void clocksource_enqueue(struct clocksource *cs) */ void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq) { + unsigned long sec; + /* - * Ideally we want to use some of the limits used in - * clocksource_max_deferment, to provide a more informed - * MAX_UPDATE_LENGTH. But for now this just gets the - * register interface working properly. + * Calc the maximum number of seconds which we can run before + * wrapping around. For clocksources which have a mask > 32bit + * we need to limit the max sleep time to have a good + * conversion precision. 10 minutes is still a reasonable + * amount. That results in a shift value of 24 for a + * clocksource with mask >= 40bit and f >= 4GHz. That maps to + * ~ 0.06ppm granularity for NTP. We apply the same 12.5% + * margin as we do in clocksource_max_deferment() */ + sec = (cs->mask - (cs->mask >> 5)); + do_div(sec, freq); + do_div(sec, scale); + if (!sec) + sec = 1; + else if (sec > 600 && cs->mask > UINT_MAX) + sec = 600; + clocks_calc_mult_shift(&cs->mult, &cs->shift, freq, - NSEC_PER_SEC/scale, - MAX_UPDATE_LENGTH*scale); + NSEC_PER_SEC / scale, sec * scale); cs->max_idle_ns = clocksource_max_deferment(cs); } EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale); @@ -678,14 +679,14 @@ EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale); int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq) { - /* Intialize mult/shift and max_idle_ns */ + /* Initialize mult/shift and max_idle_ns */ __clocksource_updatefreq_scale(cs, scale, freq); /* Add clocksource to the clcoksource list */ mutex_lock(&clocksource_mutex); clocksource_enqueue(cs); - clocksource_select(); clocksource_enqueue_watchdog(cs); + clocksource_select(); mutex_unlock(&clocksource_mutex); return 0; } @@ -705,8 +706,8 @@ int clocksource_register(struct clocksource *cs) mutex_lock(&clocksource_mutex); clocksource_enqueue(cs); - clocksource_select(); clocksource_enqueue_watchdog(cs); + clocksource_select(); mutex_unlock(&clocksource_mutex); return 0; } |