Loongson platform be designed mostly like a PC, it also control PCI
devices.
It has just one PCI bus with all devices fixed. That hardly requires the whole complexity of coreboot.
because of the payload concept, where coreboot only initializes only the minimum of the hardware and a payload, like SeaBIOS, FILO and GRUB, can take over.
I'm not quite clear about code flow between bootblock and payload for now, so, is there some document about it? or can you give some hints for code flow?
It's simple: coreboot does hardware init, bringing devices to usable state. Payload does everything else.