First try to configure or better even build the kernel. This will prepare kernel sources and make proper architecture specific symbolic links in include directory. Also make sure the include path is correct for your driver Makefile so you are not including other headers by mistake. there are tons of examples on the net how to make out of tree kernel driver. You can also check my simple kernel module example (hack to mess with mtd partition flags) for n770 http://fanoush.wz.cz/maemo/nand_rw_enable.tgz