device tree is a hardware description. meant to be load by bootloader (such as u-boot)

==read==
* https://github.com/jadonk/validation-scripts/blob/master/test-capemgr/  
* https://github.com/derekmolloy/boneDeviceTree


==videos==
* https://www.youtube.com/watch?v=wui_wU1AeQc
* https://www.youtube.com/watch?v=m_NyYEBxfn8