multi package makefile example for go

I'm trying to setup a multi package go project something like

./main.go

./subpackage1/sub1_1.go

./subpackage1/sub1_2.go

./subpackage2/sub2_1.go

./subpackage2/sub2_2.go

where main.go imports both subpackage1 and subpackage2. And subpackage2 imports subpackage1.

Ive been looking around for go makefile examples but I can't find anything that supports this kind of set-up. Any idea?