Index: include/Makefile
===================================================================
--- include/Makefile	(revision 221997)
+++ include/Makefile	(working copy)
@@ -163,7 +163,7 @@ copies:
 	    ${DESTDIR}${INCLUDEDIR}/$i
 .endfor
 	cd ${.CURDIR}/../sys/dev/acpica; \
-	${INSTALL} -C -o ${BINOWN} -g ${BINGRP} -m 444 acpiio.h \
+	${INSTALL} -C -o ${BINOWN} -g ${BINGRP} -m 444 acpi_hpet.h acpiio.h \
 	    ${DESTDIR}${INCLUDEDIR}/dev/acpica
 	cd ${.CURDIR}/../sys/dev/bktr; \
 	${INSTALL} -C -o ${BINOWN} -g ${BINGRP} -m 444 ioctl_*.h \
Index: sys/dev/acpica/acpi_hpet.c
===================================================================
--- sys/dev/acpica/acpi_hpet.c	(revision 221997)
+++ sys/dev/acpica/acpi_hpet.c	(working copy)
@@ -36,8 +36,11 @@ __FBSDID("$FreeBSD$");
 #endif
 #include <sys/param.h>
 #include <sys/bus.h>
+#include <sys/conf.h>
+#include <sys/fcntl.h>
 #include <sys/kernel.h>
 #include <sys/module.h>
+#include <sys/mman.h>
 #include <sys/proc.h>
 #include <sys/rman.h>
 #include <sys/time.h>
@@ -70,6 +73,7 @@ ACPI_MODULE_NAME("HPET")
 
 struct hpet_softc {
 	device_t		dev;
+	struct cdev		*cdev;
 	int			mem_rid;
 	int			intr_rid;
 	int			irq;
@@ -106,11 +110,54 @@ struct hpet_softc {
 	int			num_timers;
 };
 
+static d_open_t hpet_open;
+static d_mmap_t hpet_mmap;
+
 static u_int hpet_get_timecount(struct timecounter *tc);
 static void hpet_test(struct hpet_softc *sc);
 
+static struct cdevsw hpet_cdevsw = {
+	.d_version =	D_VERSION,
+	.d_open =	hpet_open,
+	.d_mmap =	hpet_mmap,
+	.d_name =	"hpet",
+};
+
 static char *hpet_ids[] = { "PNP0103", NULL };
 
+static int
+hpet_open(struct cdev *dev __unused, int oflag, int devtype __unused,
+    struct thread *td)
+{
+	struct hpet_softc *sc;
+
+	sc = devclass_get_softc(hpet_devclass, 0);
+	if (sc == NULL)
+		return (ENXIO);
+	if ((oflag & (O_CREAT | O_APPEND | O_TRUNC)) != 0)
+		return (EACCES);
+	if ((oflag & O_ACCMODE) != O_RDONLY)
+		return (securelevel_gt(td->td_ucred, 0));
+	return (0);
+}
+
+static int
+hpet_mmap(struct cdev *dev __unused, vm_ooffset_t offset, vm_paddr_t *paddr,
+    int nprot, vm_memattr_t *memattr __unused)
+{
+	struct hpet_softc *sc;
+
+	sc = devclass_get_softc(hpet_devclass, 0);
+	if (sc == NULL)
+		return (ENODEV);
+	if (offset < 0 || offset >= rman_get_size(sc->mem_res))
+		return (EINVAL);
+	if ((nprot & PROT_EXEC) != 0)
+		return (EACCES);
+	*paddr = rman_get_start(sc->mem_res) + offset;
+	return (0);
+}
+
 static u_int
 hpet_get_timecount(struct timecounter *tc)
 {
@@ -480,6 +527,9 @@ hpet_attach(device_t dev)
 		sc->tc.tc_frequency = sc->freq;
 		sc->tc.tc_priv = sc;
 		tc_init(&sc->tc);
+		/* Create /dev/hpet. */
+		sc->cdev = make_dev(&hpet_cdevsw, device_get_unit(dev),
+		    UID_ROOT, GID_WHEEL, 0644, "hpet");
 	}
 	/* If not disabled - setup and announce event timers. */
 	if (resource_int_value(device_get_name(dev), device_get_unit(dev),
@@ -697,8 +747,15 @@ hpet_attach(device_t dev)
 static int
 hpet_detach(device_t dev)
 {
+	struct hpet_softc *sc;
+
 	ACPI_FUNCTION_TRACE((char *)(uintptr_t) __func__);
 
+	if (device_get_unit(dev) == 0) {
+		sc = device_get_softc(dev);
+		destroy_dev(sc->cdev);
+	}
+
 	/* XXX Without a tc_remove() function, we can't detach. */
 	return (EBUSY);
 }