if you want to compile the driver inside kernel the prefer dir is drivers
or you can edit Makefile add something like this:
vmlinux-dirs := $(patsubst %/,%,$(filter %/, $(init-y) $(init-m) \
$(core-y) $(core-m) $(drivers-y) $(drivers-m) \
$(net-y) $(net-m) $(libs-y) $(libs-m))) \
>>>> /opt/k-guard/project/tmp/local
and the kernel can locate source at that dir