help about driver module

hi all,

my work is based nios2-linux-20120802 from www.nioswiki.com

i write a char device driver, if the driver is "compile-in" with the kernel, all things are ok!

but if the driver is compile as a loadable module, errors occurs:

ERROR: "__ioremap" [drivers/char/test.ko] undefined!

ERROR: "__iounmap" [drivers/char/test.ko] undefined!

__ioremap is defined in <asm/io.h> , which is# included in my test.c.

what's the problem?