diff options
Diffstat (limited to 'arch/x86/kernel/hpet.c')
| -rw-r--r-- | arch/x86/kernel/hpet.c | 43 |
1 files changed, 18 insertions, 25 deletions
diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c index 9b5cfcdfc426..ea230ec69057 100644 --- a/arch/x86/kernel/hpet.c +++ b/arch/x86/kernel/hpet.c @@ -17,7 +17,7 @@ /* FSEC = 10^-15 NSEC = 10^-9 */ -#define FSEC_PER_NSEC 1000000 +#define FSEC_PER_NSEC 1000000L /* * HPET address is set in acpi/boot.c, when an ACPI entry exists @@ -206,20 +206,19 @@ static void hpet_enable_legacy_int(void) static void hpet_legacy_clockevent_register(void) { - uint64_t hpet_freq; - /* Start HPET legacy interrupts */ hpet_enable_legacy_int(); /* - * The period is a femto seconds value. We need to calculate the - * scaled math multiplication factor for nanosecond to hpet tick - * conversion. + * The mult factor is defined as (include/linux/clockchips.h) + * mult/2^shift = cyc/ns (in contrast to ns/cyc in clocksource.h) + * hpet_period is in units of femtoseconds (per cycle), so + * mult/2^shift = cyc/ns = 10^6/hpet_period + * mult = (10^6 * 2^shift)/hpet_period + * mult = (FSEC_PER_NSEC << hpet_clockevent.shift)/hpet_period */ - hpet_freq = 1000000000000000ULL; - do_div(hpet_freq, hpet_period); - hpet_clockevent.mult = div_sc((unsigned long) hpet_freq, - NSEC_PER_SEC, hpet_clockevent.shift); + hpet_clockevent.mult = div_sc((unsigned long) FSEC_PER_NSEC, + hpet_period, hpet_clockevent.shift); /* Calculate the min / max delta */ hpet_clockevent.max_delta_ns = clockevent_delta2ns(0x7FFFFFFF, &hpet_clockevent); @@ -324,7 +323,7 @@ static struct clocksource clocksource_hpet = { static int hpet_clocksource_register(void) { - u64 tmp, start, now; + u64 start, now; cycle_t t1; /* Start the counter */ @@ -351,21 +350,15 @@ static int hpet_clocksource_register(void) return -ENODEV; } - /* Initialize and register HPET clocksource - * - * hpet period is in femto seconds per cycle - * so we need to convert this to ns/cyc units - * approximated by mult/2^shift - * - * fsec/cyc * 1nsec/1000000fsec = nsec/cyc = mult/2^shift - * fsec/cyc * 1ns/1000000fsec * 2^shift = mult - * fsec/cyc * 2^shift * 1nsec/1000000fsec = mult - * (fsec/cyc << shift)/1000000 = mult - * (hpet_period << shift)/FSEC_PER_NSEC = mult + /* + * The definition of mult is (include/linux/clocksource.h) + * mult/2^shift = ns/cyc and hpet_period is in units of fsec/cyc + * so we first need to convert hpet_period to ns/cyc units: + * mult/2^shift = ns/cyc = hpet_period/10^6 + * mult = (hpet_period * 2^shift)/10^6 + * mult = (hpet_period << shift)/FSEC_PER_NSEC */ - tmp = (u64)hpet_period << HPET_SHIFT; - do_div(tmp, FSEC_PER_NSEC); - clocksource_hpet.mult = (u32)tmp; + clocksource_hpet.mult = div_sc(hpet_period, FSEC_PER_NSEC, HPET_SHIFT); clocksource_register(&clocksource_hpet); |
