Hi,
Seems this is similar to the overflow problem in the high resolution
sched_clock(), If not ensure the 'mult' is in 32bit, we must use the
128bit calculation in the common function clocksource_cyc2ns() defined
in include/linux/clocksource.h.
Regards,
Wu Zhangjin
On Tue, 2010-05-18 at 15:11 -0700, David Daney wrote:
> The 'mult' element of struct clock_event_device must never be wider
> than 32-bits. If it were, it would get truncated when used by
> clockevent_delta2ns() when this calls do_div().
>
> We meet the requirement by ensuring that the relationship:
>
> (mips_hpt_frequency >> (32 - shift)) < NSEC_PER_SEC
>
> Always holds.
>
> Signed-off-by: David Daney <ddaney@xxxxxxxxxxxxxxxxxx>
> CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
> arch/mips/kernel/cevt-r4k.c | 16 +++++++++++++---
> 1 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/arch/mips/kernel/cevt-r4k.c b/arch/mips/kernel/cevt-r4k.c
> index 0b2450c..4495158 100644
> --- a/arch/mips/kernel/cevt-r4k.c
> +++ b/arch/mips/kernel/cevt-r4k.c
> @@ -163,10 +163,11 @@ int c0_compare_int_usable(void)
>
> int __cpuinit r4k_clockevent_init(void)
> {
> - uint64_t mips_freq = mips_hpt_frequency;
> + uint64_t scaled_freq = mips_hpt_frequency;
> unsigned int cpu = smp_processor_id();
> struct clock_event_device *cd;
> unsigned int irq;
> + int shift;
>
> if (!cpu_has_counter || !mips_hpt_frequency)
> return -ENXIO;
> @@ -189,8 +190,17 @@ int __cpuinit r4k_clockevent_init(void)
> cd->features = CLOCK_EVT_FEAT_ONESHOT;
>
> /* Calculate the min / max delta */
> - cd->mult = div_sc((unsigned long) mips_freq, NSEC_PER_SEC, 32);
> - cd->shift = 32;
> + shift = 32;
> + while (scaled_freq >= NSEC_PER_SEC && shift) {
> + scaled_freq = scaled_freq >> 1;
> + shift--;
> + }
> + BUG_ON(shift == 0);
> +
> + cd->mult = div_sc((unsigned long) mips_hpt_frequency,
> + NSEC_PER_SEC, shift);
> + cd->shift = shift;
> +
> cd->max_delta_ns = clockevent_delta2ns(0x7fffffff, cd);
> cd->min_delta_ns = clockevent_delta2ns(0x300, cd);
>
