netdev - Re: Phy access methods for copper SFP+ disguised as SR

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Message-ID: <eb92da6a-b614-4deb-9321-df5a57ed987d@lunn.ch>
Date: Mon, 24 Feb 2025 14:18:17 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Bjørn Mork <bjorn@...k.no>
Cc: netdev@...r.kernel.org
Subject: Re: Phy access methods for copper SFP+ disguised as SR

On Sun, Feb 23, 2025 at 12:34:04PM +0100, Bjørn Mork wrote:
> Got myself a couple of cheap 10GBase-T SFP+s and am struggling to figure
> out how to talk to the phy.  The phy does not appear to be directly
> accessible on 0x56, and it does not respond using the Rollball protocol
> either.
> 
> Are there any other well known methods out there, or am I stuck with
> whatever SR emulation the SFP vendor implemented?

Those are the two i know of. The problem is, copper SFP modules are
not part of any standard, so manufactures are free to do whatever they
want.

For 1G, the Marvell 88e1111 is often used, since it has a built in i2c
device. For 10G the Marvell 88X3310 is often used, but that does not
have i2c, as far as i know, and there is a small microprocessor which
implements the Rollball protocol, talking MDIO to the PHY. Since it is
not build into the PHY the MCU could well be talking a different
protocol.

	Andrew