Source

The Rockchip Linux SDK source tree is located in multi Git repository hosted by Github(https://github.com/rockchip-linux). The SDK uses repo to sync down source code.
Create an empty directory to hold your working files.

git clone https://github.com/rockchip-linux/repo
mkdir linux
cd linux

To download RK3399 Linux SDK: 

../repo/repo init --repo-url=https://github.com/rockchip-linux/repo -u https://github.com/rockchip-linux/manifests -b master -m rk3399_linux_release.xml 
../repo/repo sync

To download RK3288 Linux SDK: 

../repo/repo init --repo-url=https://github.com/rockchip-linux/repo -u https://github.com/rockchip-linux/manifests -b master -m rk3288_linux_release.xml
../repo/repo sync

To download RK3328 Linux SDK: 

../repo/repo init --repo-url=https://github.com/rockchip-linux/repo -u https://github.com/rockchip-linux/manifests -b master -m rk3328_linux_release.xml
../repo/repo sync