phylink and an unusual PHY/SFP setup

phylink and an unusual PHY/SFP setup

[Michael Walle]

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Hi,

I have a board with a rather unusual network link setup:

 MAC/PCS (fman) <-SerDes-> PHY (M88E1112) <-SerDes-> SFP

or even

 MAC/PCS (fman) <-SerDes-> PHY (M88E1112) <-SerDes-> Copper SFP with PHY

Does phylink support such a configuration? I suspect adding
support for such a configuration isn't straight forward.

FWIW, the M88E1112 PHY driver seems to be completely broken in
upstream. It looks like it was assumed, that it's like the M88E1111.
But that one only has 1 SerDes and one parallel interface. The 1112
has two SerDes interfaces and thus a completely different register
map. I'm not sure it ever worked, except maybe by accident for the
SGMII-to-Copper case.

-michael

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Re: phylink and an unusual PHY/SFP setup

[Andrew Lunn]

On Wed, May 27, 2026 at 10:19:18AM +0200, Michael Walle wrote:
> Hi,
> 
> I have a board with a rather unusual network link setup:
> 
>  MAC/PCS (fman) <-SerDes-> PHY (M88E1112) <-SerDes-> SFP
> 
> or even
> 
>  MAC/PCS (fman) <-SerDes-> PHY (M88E1112) <-SerDes-> Copper SFP with PHY

Such setups do exist already, but with a different PHY. The Marvel 10G
PHY is sometimes placed in the middle like this. And there are other
PHYs.

Take a look at

commit 35d1a5464b476aa98b7b76ce41bb4de748cebfc2
Author: Maxime Chevallier <maxime.chevallier@bootlin.com>
Date:   Thu Jan 8 09:00:35 2026 +0100

    net: phy: marvell10g: Support SFP through phy_port
    
    Convert the Marvell10G driver to use the generic SFP handling, through a
    dedicated .attach_port() handler to populate the port's supported
    interfaces.
    
    As the 88x3310 supports multiple MDI, the .attach_port() logic handles
    both SFP attach with 10GBaseR support, and support for the "regular"
    port that usually is a BaseT port.

Also, marvell-88x2222.c.

	Andrew