1 files changed, 67 insertions, 0 deletions

diff --git a/arch/i386/kernel/hpet.c b/arch/i386/kernel/hpet.c
new file mode 100644
index 000000000000..91a5bdd9f604
--- /dev/null
+++ b/arch/i386/kernel/hpet.c
@@ -0,0 +1,67 @@
+#include <linux/clocksource.h>
+#include <linux/errno.h>
+#include <linux/hpet.h>
+#include <linux/init.h>
+
+#include <asm/hpet.h>
+#include <asm/io.h>
+
+#define HPET_MASK       0xFFFFFFFF
+#define HPET_SHIFT      22
+
+/* FSEC = 10^-15 NSEC = 10^-9 */
+#define FSEC_PER_NSEC   1000000
+
+static void *hpet_ptr;
+
+static cycle_t read_hpet(void)
+{
+        return (cycle_t)readl(hpet_ptr);
+}
+
+static struct clocksource clocksource_hpet = {
+        .name           = "hpet",
+        .rating         = 250,
+        .read           = read_hpet,
+        .mask           = (cycle_t)HPET_MASK,
+        .mult           = 0, /* set below */
+        .shift          = HPET_SHIFT,
+        .is_continuous  = 1,
+};
+
+static int __init init_hpet_clocksource(void)
+{
+        unsigned long hpet_period;
+        void __iomem* hpet_base;
+        u64 tmp;
+
+        if (!hpet_address)
+                return -ENODEV;
+
+        /* calculate the hpet address: */
+        hpet_base =
+                (void __iomem*)ioremap_nocache(hpet_address, HPET_MMAP_SIZE);
+        hpet_ptr = hpet_base + HPET_COUNTER;
+
+        /* calculate the frequency: */
+        hpet_period = readl(hpet_base + HPET_PERIOD);
+
+        /*
+         * hpet period is in femto seconds per cycle
+         * so we need to convert this to ns/cyc units
+         * aproximated 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
+         */
+        tmp = (u64)hpet_period << HPET_SHIFT;
+        do_div(tmp, FSEC_PER_NSEC);
+        clocksource_hpet.mult = (u32)tmp;
+
+        return register_clocksource(&clocksource_hpet);
+}
+
+module_init(init_hpet_clocksource);