If only something newer than RV710 documentation would leak out

Stop looking for the info on a silver platter, and start getting creative. In this case - you don't even have to get creative, such as looking in the AMDGPU driver code, because it's in the GDDR5 specifications from JEDEC.
I was looking there first, but they ask money for it

RV710 documentation is not "information on a silver platter", its just databook that is NDA-ed, for some reason
Edit: just checked, either they removed fee for downloading, or I was high when I checked few months ago...still,
they'll tell me everything about gddr5, but how that transfers into AMD strap is still AMD bussiness