linux-kernel - Re: [EXT] Re: [PATCH net-next 2/9] dt-bindings: net: add backplane dt bindings

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Message-ID: <20200327154448.GK11004@lunn.ch>
Date:   Fri, 27 Mar 2020 16:44:48 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Florinel Iordache <florinel.iordache@....com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "corbet@....net" <corbet@....net>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Leo Li <leoyang.li@....com>,
        "Madalin Bucur (OSS)" <madalin.bucur@....nxp.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [EXT] Re: [PATCH net-next 2/9] dt-bindings: net: add backplane
 dt bindings

> What worries me is the situation which I've been working on, where
> we want access to the PCS PHYs, and we can't have the PCS PHYs
> represented as a phylib PHY because we may have a copper PHY behind
> the PCS PHY, and we want to be talking to the copper PHY in the
> first instance (the PCS PHY effectivel ybecomes a slave to the
> copper PHY.)

I guess we need to clarify what KR actually means. If we have a
backplane with a MAC on each end, i think modelling it as a PHY could
work.

If however, we have a MAC connected to a backplane, and on the end of
the backplane is a traditional PHY, or an SFP cage, we have problems.
As your point out, we cannot have two PHYs in a chain for one MAC.

But i agree with Russell. We need a general solution of how we deal
with PCSs.

   Andrew