From Fedora Project Wiki
The Loongson CPU is not just a MIPS64, it needs special fixes on compilaton (see this http://sourceware.org/ml/binutils/2009-11/msg00387.html ) , and it has extra multimedia instruction-set that should be supported by us.
So I suggest the primary target Loongson, and, the next step, adding a standard MIPS32-softfloat target for those mips-soc-based mobile devices. Even a multilib (/lib32, /lib64) solution is considerable.