Build the ds1672 driver as a module. Add a detach() to unregister the rtc.

sys/dev/iicbus/ds1672.c

@@ -117,6 +117,14 @@ ds1672_init(device_t dev)
 	return (error);
 }
 
+static int
+ds1672_detach(device_t dev)
+{
+
+    clock_unregister(dev);
+    return (0);
+}
+
 static int
 ds1672_attach(device_t dev)
 {
@@ -166,6 +174,7 @@ ds1672_settime(device_t dev, struct timespec *ts)
 static device_method_t ds1672_methods[] = {
 	DEVMETHOD(device_probe,		ds1672_probe),
 	DEVMETHOD(device_attach,	ds1672_attach),
+	DEVMETHOD(device_detach,	ds1672_detach),
 
 	DEVMETHOD(clock_gettime,	ds1672_gettime),
 	DEVMETHOD(clock_settime,	ds1672_settime),

sys/modules/i2c/Makefile

@@ -5,6 +5,7 @@ SUBDIR = \
 	cyapa \
 	ds1307 \
 	ds13rtc \
+	ds1672 \
 	ds3231 \
 	icee \
 	if_ic \

sys/modules/i2c/ds1672/Makefile

@@ -0,0 +1,19 @@
+# $FreeBSD$
+
+.PATH:	${SRCTOP}/sys/dev/iicbus
+KMOD	= ds1672
+SRCS	= ds1672.c 
+
+# Generated files...
+SRCS+=	\
+	bus_if.h \
+	clock_if.h \
+	device_if.h \
+	iicbus_if.h \
+	opt_platform.h \
+
+.if !empty(OPT_FDT)
+SRCS+=	ofw_bus_if.h
+.endif
+
+.include <bsd.kmod.mk>