I have never seen source code for RK3188 kernel. Maybe you will need to adapt nwer rockchip 4.4x kernel, but I don't think you gain anything. RK3188 is very old and just a kernel bump is not gonna make anything new to be honest. But I don't have that source code. I provided all sources I had, but never saw any commit or changes used when using those sources, and that is not a community, so I shut down my github and is private right now. Because there is point sharing code that people fork and don't release changes when releasing a new kernel.