linux-kernel - Re: [RFC PATCH net-next 8/8] dt-bindings: net: fsl,backplane-anlt: new binding document

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Message-ID: <e3afb3d5-6efe-46de-81ca-7f0163c4b04d@lunn.ch>
Date:   Mon, 21 Aug 2023 22:20:43 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     Rob Herring <robh@...nel.org>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-phy@...ts.infradead.org,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Madalin Bucur <madalin.bucur@....com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Camelia Groza <camelia.groza@....com>,
        Li Yang <leoyang.li@....com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor@...nel.org>,
        Sean Anderson <sean.anderson@...o.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>
Subject: Re: [RFC PATCH net-next 8/8] dt-bindings: net: fsl,backplane-anlt:
 new binding document

> > >        - items:
> > >            - pattern: "^ethernet-phy-id[a-f0-9]{4}\\.[a-f0-9]{4}$"
> > >            - const: ethernet-phy-ieee802.3-c45
> > > +      - items:
> > > +          - const: fsl,lx2160a-backplane-anlt
> > > +          - const: ethernet-phy-ieee802.3-c45
> > 
> > What's the benefit of having ethernet-phy-ieee802.3-c45? Will it work if 
> > the OS only understands that and not fsl,lx2160a-backplane-anlt?
> 
> No. The "is_c45" bool won't get set correctly in fwnode_mdiobus_register_phy().
> 
> 	is_c45 = fwnode_device_is_compatible(child, "ethernet-phy-ieee802.3-c45");
> 
> With that bool set incorrectly, the MDIO protocol cannot access the device's
> registers.
> 
> > > +        description:
> > > +          Some C45 PHYs have no PHY ID in the standard location, and there is
> > > +          also no PHY ID allocated for them to fake. They are identified by the
> > > +          primary compatible string, plus the secondary one to distinguish them
> > > +          from a raw MDIO device.

Could you fake ID registers? Is this on any arbitrary MDIO bus, or an
internal bus with its own MDIO driver which could trap reads to the ID
registers and return well known values?

	Andrew