On Thu, 21 Jul 2022 21:22:16 +0300 Vladimir Oltean <olteanv@xxxxxxxxx> wrote: > On Thu, Jul 21, 2022 at 07:21:45PM +0200, Marek Behún wrote: > > Marvell documentation says that 2500base-x does not implement inband > > AN. > > Does Marvell documentation actually call it 2500base-x when it says it > doesn't support in-band autoneg? Yes, it does. > > But when it was first implemented, for some reason it was thought that > > 2500base-x is just 1000base-x at 2.5x speed, and 1000base-x does > > support inband AN. Also it worked during tests for both switches and > > SOC NICs, so it was enabled. > > > > At the time 2500base-x was not standardized. Now 2500base-x is > > stanradrized, and the standard says that 2500base-x does not support > > clause 37 AN. I guess this is because where it is used, it is intended > > to work with clause 73 AN somehow. > > When you say 2500base-x is standardized, do you mean there is a document > somewhere which I could use to read more about this? IEEE Std 802.3cb-2018: Amendment 1: Physical Layer Specifications and Management Parameters for 2.5 Gb/s and 5 Gb/s Operation over Backplane. Annex 127A (informative): Compatibility of 2.5GBASE-X PCS/PMA with 1000BASE-X PCS/PMA running 2.5 times faster ... This annex discusses the restrictions when operating 2.5GBASE-X PCS/PMA with a 1000BASE-X PCS/PMA link partner running 2.5 times faster. Compatibility of the PMD is outside the scope of this annex. In this annex when 1000BASE-X PCS/PMA is referred to, the 2.5 times speed up is implied. ... The 2.5GBASE-X PCS does not support Clause 37 Auto-Negotiation. Hence, the 1000BASE-X PCS is expected to have its Clause 37 Auto-Negotiation functionality disabled so that the /C/ ordered set will not be transmitted. If a 2.5GBASE-X PCS receives /C/ ordered set, then undefined behavior may occur. ... Marek
