libsigrokdecode supports yet another protocol decoder since a while ago (which hasn't seen an official announce yet, though): mdio.
This is a PD for decoding the Management Data Input/Output (MDIO) protocol, sometimes also referred to as Serial Management Interface (SMI) or Media Independent Interface Management (MIIM).
As always, we have a few example files in the sigrok-dumps repo and some test-cases in the sigrok-test repo.
The decoder was contributed by Aurelien Jacobs, thanks a lot!
