This site links to https://areweloongyet.com/en/

> Even though the Loongson Corporation has yet to release the remaining volumes of the LoongArch manual, thanks to a wealth of public information such as publicly available QEMU and Linux changes, "undisclosed" information such as instruction encoding and behaviors is, in effect, already public. The absence of manuals can no longer hinder optimization efforts by The People.

If the architecture is still undocumented, I would not consider Debian’s move to be wise.