Index: head/sys/boot/kshim/bsd_busspace.c
===================================================================
--- head/sys/boot/kshim/bsd_busspace.c
+++ head/sys/boot/kshim/bsd_busspace.c
@@ -37,6 +37,15 @@
 	uint32_t dw7;
 };
 
+int
+bus_space_subregion(bus_space_tag_t t, bus_space_handle_t bsh,
+    bus_size_t offset, bus_size_t size, bus_space_handle_t *nbshp)
+{
+
+	*nbshp = bsh + offset;
+	return (0);
+}
+
 void
 bus_space_read_multi_1(bus_space_tag_t t, bus_space_handle_t h,
     bus_size_t offset, uint8_t *datap, bus_size_t count)
Index: head/sys/boot/kshim/bsd_kernel.h
===================================================================
--- head/sys/boot/kshim/bsd_kernel.h
+++ head/sys/boot/kshim/bsd_kernel.h
@@ -397,6 +397,8 @@
 int	bus_generic_suspend(device_t dev);
 int	bus_generic_print_child(device_t dev, device_t child);
 void	bus_generic_driver_added(device_t dev, driver_t *driver);
+int	bus_space_subregion(bus_space_tag_t t, bus_space_handle_t bsh,
+    bus_size_t offset, bus_size_t size, bus_space_handle_t *nbshp);
 
 /* BUS SPACE API */