board:		|--some board info and some parameters pass to kernel

common:		|-------------------------------
		|--bus: probe driver and device
		|--mmc: mmc subsystem
		|--usb: usb subsystem
		|--flash: flash subsystem
		|--interrupt: interrupt subsystem
		|--------------------------------

drivers:	|--just some driver about diffrent platform

platform:	|--diffrent platform

tool:		|--some tool,like fastboot....