1 files changed, 19 insertions, 13 deletions

diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index b619ca5eaf8c..a1eb14e6d9f7 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -78,7 +78,7 @@ struct hpets {
         struct hpet __iomem *hp_hpet;
         unsigned long hp_hpet_phys;
         struct time_interpolator *hp_interpolator;
-        unsigned long hp_period;
+        unsigned long long hp_tick_freq;
         unsigned long hp_delta;
         unsigned int hp_ntimer;
         unsigned int hp_which;
@@ -427,12 +427,14 @@ static int hpet_ioctl_ieon(struct hpet_dev *devp)
         return 0;
 }
 
-static inline unsigned long hpet_time_div(unsigned long dis)
+/* converts Hz to number of timer ticks */
+static inline unsigned long hpet_time_div(struct hpets *hpets,
+                                          unsigned long dis)
 {
-        unsigned long long m = 1000000000000000ULL;
+        unsigned long long m;
 
+        m = hpets->hp_tick_freq + (dis >> 1);
         do_div(m, dis);
-
         return (unsigned long)m;
 }
 
@@ -480,7 +482,7 @@ hpet_ioctl_common(struct hpet_dev *devp, int cmd, unsigned long arg, int kernel)
                 {
                         struct hpet_info info;
 
-                        info.hi_ireqfreq = hpet_time_div(hpetp->hp_period *
+                        info.hi_ireqfreq = hpet_time_div(hpetp,
                                                          devp->hd_ireqfreq);
                         info.hi_flags =
                             readq(&timer->hpet_config) & Tn_PER_INT_CAP_MASK;
@@ -524,7 +526,7 @@ hpet_ioctl_common(struct hpet_dev *devp, int cmd, unsigned long arg, int kernel)
                         break;
                 }
 
-                devp->hd_ireqfreq = hpet_time_div(hpetp->hp_period * arg);
+                devp->hd_ireqfreq = hpet_time_div(hpetp, arg);
         }
 
         return err;
@@ -713,7 +715,7 @@ static void hpet_register_interpolator(struct hpets *hpetp)
         ti->source = TIME_SOURCE_MMIO64;
         ti->shift = 10;
         ti->addr = &hpetp->hp_hpet->hpet_mc;
-        ti->frequency = hpet_time_div(hpets->hp_period);
+        ti->frequency = hpetp->hp_tick_freq;
         ti->drift = HPET_DRIFT;
         ti->mask = -1;
 
@@ -750,7 +752,7 @@ static unsigned long hpet_calibrate(struct hpets *hpetp)
         t = read_counter(&timer->hpet_compare);
 
         i = 0;
-        count = hpet_time_div(hpetp->hp_period * TICK_CALIBRATE);
+        count = hpet_time_div(hpetp, TICK_CALIBRATE);
 
         local_irq_save(flags);
 
@@ -775,7 +777,8 @@ int hpet_alloc(struct hpet_data *hdp)
         size_t siz;
         struct hpet __iomem *hpet;
         static struct hpets *last = (struct hpets *)0;
-        unsigned long ns;
+        unsigned long ns, period;
+        unsigned long long temp;
 
         /*
          * hpet_alloc can be called by platform dependent code.
@@ -825,8 +828,12 @@ int hpet_alloc(struct hpet_data *hdp)
 
         last = hpetp;
 
-        hpetp->hp_period = (cap & HPET_COUNTER_CLK_PERIOD_MASK) >>
-            HPET_COUNTER_CLK_PERIOD_SHIFT;
+        period = (cap & HPET_COUNTER_CLK_PERIOD_MASK) >>
+                HPET_COUNTER_CLK_PERIOD_SHIFT; /* fs, 10^-15 */
+        temp = 1000000000000000uLL; /* 10^15 femtoseconds per second */
+        temp += period >> 1; /* round */
+        do_div(temp, period);
+        hpetp->hp_tick_freq = temp; /* ticks per second */
 
         printk(KERN_INFO "hpet%d: at MMIO 0x%lx, IRQ%s",
                 hpetp->hp_which, hdp->hd_phys_address,
@@ -835,8 +842,7 @@ int hpet_alloc(struct hpet_data *hdp)
                 printk("%s %d", i > 0 ? "," : "", hdp->hd_irq[i]);
         printk("\n");
 
-        ns = hpetp->hp_period;  /* femptoseconds, 10^-15 */
-        ns /= 1000000;          /* convert to nanoseconds, 10^-9 */
+        ns = period / 1000000;  /* convert to nanoseconds, 10^-9 */
         printk(KERN_INFO "hpet%d: %ldns tick, %d %d-bit timers\n",
                 hpetp->hp_which, ns, hpetp->hp_ntimer,
                 cap & HPET_COUNTER_SIZE_MASK ? 64 : 32);