netdev - Re: net: phy: Dealing with 88e1543 dual-port mode

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Date:   Thu, 19 Nov 2020 23:43:39 +0100
From:   Tobias Waldekranz <tobias@...dekranz.com>
To:     Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Antoine Tenart <atenart@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: net: phy: Dealing with 88e1543 dual-port mode

On Thu, Nov 19, 2020 at 16:24, Maxime Chevallier <maxime.chevallier@...tlin.com> wrote:
> I don't think we have a way to distinguish from the DT if we are in
> SGMII-to-Fibre or in SGMII-to-{Copper + Fibre}, since the description is
> the same, we don't have any information in DT about wether or not the
> PHY is wired to a Copper RJ45 port.
>
> Maybe we should have a way to indicate if a PHY is wired to a Copper
> port in DT ?

Do you mean something like:

SGMII->SGMII (Fibre):
ethernet-phy@0 {
   sfp = <&sfp0>;
};

SGMII->MDI (Copper):
ethernet-phy@0 {
    mdi;
};

SGMII->Auto Media Detect
ethernet-phy@0 {
    mdi;
    sfp = <&sfp0>;
};

If so, this could also be useful in scenarios that have nothing to do
with combo ports, but where you have custom connectors.

E.g. at Westermo we make switches with M12/M12X connectors [1] that
sometimes have a 1G PHY behind a 2-pair M12 connector (for complicated
legacy reasons). In such cases we have to remove 1000-HD/FD from the
advertised link modes. Being able to describe that in the DT with
something like:

ethernet-phy@0 {
    mdi = "2-pair";
};

Would be great!

On the topic of combo ports, another thing to consider is how this
should play with ethtool. Ideally it would be aware of the two media
sides, and be able to configure them both independently.

[1]: https://www.westermo.com/products/ethernet-switches/en50155/viper-208-t4g-tbn