diff options
Diffstat (limited to 'kernel/time/clocksource.c')
| -rw-r--r-- | kernel/time/clocksource.c | 26 |
1 files changed, 12 insertions, 14 deletions
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 2148f413256c..ace95763b3a6 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -469,6 +469,9 @@ static u32 clocksource_max_adjustment(struct clocksource *cs) * @shift: cycle to nanosecond divisor (power of two) * @maxadj: maximum adjustment value to mult (~11%) * @mask: bitmask for two's complement subtraction of non 64 bit counters + * + * NOTE: This function includes a safety margin of 50%, so that bad clock values + * can be detected. */ u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask) { @@ -490,11 +493,14 @@ u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask) max_cycles = min(max_cycles, mask); max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift); + /* Return 50% of the actual maximum, so we can detect bad values */ + max_nsecs >>= 1; + return max_nsecs; } /** - * clocksource_max_deferment - Returns max time the clocksource can be deferred + * clocksource_max_deferment - Returns max time the clocksource should be deferred * @cs: Pointer to clocksource * */ @@ -504,13 +510,7 @@ static u64 clocksource_max_deferment(struct clocksource *cs) max_nsecs = clocks_calc_max_nsecs(cs->mult, cs->shift, cs->maxadj, cs->mask); - /* - * To ensure that the clocksource does not wrap whilst we are idle, - * limit the time the clocksource can be deferred by 12.5%. Please - * note a margin of 12.5% is used because this can be computed with - * a shift, versus say 10% which would require division. - */ - return max_nsecs - (max_nsecs >> 3); + return max_nsecs; } #ifndef CONFIG_ARCH_USES_GETTIMEOFFSET @@ -659,10 +659,9 @@ void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq) * 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() + * ~ 0.06ppm granularity for NTP. */ - sec = (cs->mask - (cs->mask >> 3)); + sec = cs->mask; do_div(sec, freq); do_div(sec, scale); if (!sec) @@ -674,9 +673,8 @@ void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq) NSEC_PER_SEC / scale, sec * scale); /* - * for clocksources that have large mults, to avoid overflow. - * Since mult may be adjusted by ntp, add an safety extra margin - * + * Ensure clocksources that have large 'mult' values don't overflow + * when adjusted. */ cs->maxadj = clocksource_max_adjustment(cs); while ((cs->mult + cs->maxadj < cs->mult) |