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 0000000000000..91a5bdd9f604c
--- /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);