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);