diff options
| -rw-r--r-- | kernel/time/clockevents.c | 65 |
1 files changed, 50 insertions, 15 deletions
diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c index 38959c866789..662c5798a685 100644 --- a/kernel/time/clockevents.c +++ b/kernel/time/clockevents.c @@ -33,29 +33,64 @@ struct ce_unbind { int res; }; -/** - * clockevents_delta2ns - Convert a latch value (device ticks) to nanoseconds - * @latch: value to convert - * @evt: pointer to clock event device descriptor - * - * Math helper, returns latch value converted to nanoseconds (bound checked) - */ -u64 clockevent_delta2ns(unsigned long latch, struct clock_event_device *evt) +static u64 cev_delta2ns(unsigned long latch, struct clock_event_device *evt, + bool ismax) { u64 clc = (u64) latch << evt->shift; + u64 rnd; if (unlikely(!evt->mult)) { evt->mult = 1; WARN_ON(1); } + rnd = (u64) evt->mult - 1; + + /* + * Upper bound sanity check. If the backwards conversion is + * not equal latch, we know that the above shift overflowed. + */ + if ((clc >> evt->shift) != (u64)latch) + clc = ~0ULL; + + /* + * Scaled math oddities: + * + * For mult <= (1 << shift) we can safely add mult - 1 to + * prevent integer rounding loss. So the backwards conversion + * from nsec to device ticks will be correct. + * + * For mult > (1 << shift), i.e. device frequency is > 1GHz we + * need to be careful. Adding mult - 1 will result in a value + * which when converted back to device ticks can be larger + * than latch by up to (mult - 1) >> shift. For the min_delta + * calculation we still want to apply this in order to stay + * above the minimum device ticks limit. For the upper limit + * we would end up with a latch value larger than the upper + * limit of the device, so we omit the add to stay below the + * device upper boundary. + * + * Also omit the add if it would overflow the u64 boundary. + */ + if ((~0ULL - clc > rnd) && + (!ismax || evt->mult <= (1U << evt->shift))) + clc += rnd; do_div(clc, evt->mult); - if (clc < 1000) - clc = 1000; - if (clc > KTIME_MAX) - clc = KTIME_MAX; - return clc; + /* Deltas less than 1usec are pointless noise */ + return clc > 1000 ? clc : 1000; +} + +/** + * clockevents_delta2ns - Convert a latch value (device ticks) to nanoseconds + * @latch: value to convert + * @evt: pointer to clock event device descriptor + * + * Math helper, returns latch value converted to nanoseconds (bound checked) + */ +u64 clockevent_delta2ns(unsigned long latch, struct clock_event_device *evt) +{ + return cev_delta2ns(latch, evt, false); } EXPORT_SYMBOL_GPL(clockevent_delta2ns); @@ -380,8 +415,8 @@ void clockevents_config(struct clock_event_device *dev, u32 freq) sec = 600; clockevents_calc_mult_shift(dev, freq, sec); - dev->min_delta_ns = clockevent_delta2ns(dev->min_delta_ticks, dev); - dev->max_delta_ns = clockevent_delta2ns(dev->max_delta_ticks, dev); + dev->min_delta_ns = cev_delta2ns(dev->min_delta_ticks, dev, false); + dev->max_delta_ns = cev_delta2ns(dev->max_delta_ticks, dev, true); } /** |