Re: Aquantia PHY in OCSGMII mode?

[Vladimir Oltean <vladimir.oltean@nxp.com>]

On Wed, Aug 27, 2025 at 10:13:59AM +0100, Russell King (Oracle) wrote:
> On Wed, Aug 27, 2025 at 11:03:42AM +0200, Alexander Wilhelm wrote:
> > I asked the hardware engineer again. The point is that the MAC does not set
> > SGMII for 100M. It still uses 2500base-x but with 10x paket repetition.
> 
> No one uses symbol repetition when in 2500base-x mode. Nothing supports
> it. Every device datasheet I've read states clearly that symbol
> repetition is unsupported when operating at 2.5Gbps.
> 
> Also think about what this means. If the link is operating at 2.5Gbps
> with a 10x symbol repetition, that means the link would be passing
> 250Mbps. That's not compatible with _anything_.

FWIW, claim 5 of this active Cisco patent suggests dividing frames into
2 segments, replicating symbols from the first segment twice and symbols
from the second segment three times.
https://patents.google.com/patent/US7356047B1/en

I'm completely unaware of any implementations of this either, though.

To remain on topic, I don't see how the hardware engineer's claim can be
true. The PCS symbol replication is done through the IF_MODE_SPEED
field, which lynx_pcs_link_up_2500basex() sets to SGMII_SPEED_2500 (same
as SGMII_SPEED_1000, i.e. no replication). You can confirm that the
IF_MODE register has the expected value by putting a print.