https://www.pcgamer.com/a-linux-update-may-have-let-slip-amd-big-navis-mammoth-core/
Details for two GPUs codenamed Sienna Cichlid (Navi 21, or Big Navi) and Navy Flounder (Navi 22 or 23) were revealed. Of most interest here is the fact that Big Navi does appear to confirm the rumours that it will be a 80 CU (Compute Unit) chip, while Navy Flounder appears to have 40 CUs. Multiply the top three numbers in the table to get the CU count. According to the document Big Navi will have a 256-bit memory bus, while Navy Flounder appears to have a 192-bit memory bus.