Linux machine for source code compilation
If you are planning to compile your own i.MX6 uBoot & Linux, you will need to setup a Linux host. Follow these steps to prepare one: https://github.com/FEDEVEL/imx6rex-u-boot-2009.08/wiki
(Note: Later I will upload my virtual machine, so you dont have to install everything by yourself.)
uBoot Source code
The initial version of iMX6 Rex uBoot source code can be found at: https://github.com/FEDEVEL/imx6rex-u-boot-2009.08