Re: [net-next RFC PATCH 03/14] dt-bindings: net: document ethernet PHY package nodes

[Russell King (Oracle)]

On Fri, Nov 24, 2023 at 03:44:20PM +0100, Andrew Lunn wrote:
> > 		First Serdes mode	Second Serdes mode
> > Option 1	PSGMII for copper	Disabled
> > 		ports 0-4
> > Option 2	PSGMII for copper	1000BASE-X / 100BASE-FX
> > 		ports 0-4
> > Option 3	QSGMII for copper	SGMII for
> > 		ports 0-3		copper port 4
> 
> With option 2, can the second SERDES also do SGMII? You are likely to
> need that when a Copper SFP module is inserted into the cage.

The document states "The fiber port supports 1000BASE-X/100BASE-FX".

The same is true of Marvell 88x3310's fiber port - it supports only
fiber not SGMII. This is actually something else that - when the
patches for stacked PHYs mature - will need to be addressed. If we
have a 1G copper SFP plugged into an interface that only supports
1000base-X then we need a way to switch the PHY on the SFP module
to 1000base-X if it's in SGMII mode.

Some copper SFPs come up in 1000base-X mode, and we currently rely
on the 88e1111 driver to switch them to SGMII mode. Others do want
SGMII mode (like Mikrotik RJ01 where the PHY is inaccessible and
thus can't be reconfigured.)

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