Hi, Yu,
Linux kernel command line is in linux-c6x-project/kbuilds. Please refer to the instruction in building kernel in http://linux-c6x.org/wiki/index.php/Serial_RapidIO#Building_the_Serial_RapidIO_package_sources if you have not seen this document. The C6678 dip switch should be set according to http://processors.wiki.ti.com/index.php/TMDXEVM6678L_EVM_Hardware_Setup#Boot_Mode_Dip_Switch_Settings
Could you elaborate more on "can't load the linux kernel"?
Rex