netdev - Re: [RFC PATCH net-next 0/9] net: pcs: Add support for devices probed in the "usual" manner

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Message-ID: <20220719152539.i43kdp7nolbp2vnp@skbuf>
Date:   Tue, 19 Jul 2022 18:25:39 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Sean Anderson <sean.anderson@...o.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        Madalin Bucur <madalin.bucur@....com>,
        "David S . Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Andrew Lunn <andrew@...n.ch>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Frank Rowand <frowand.list@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Li Yang <leoyang.li@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Rob Herring <robh+dt@...nel.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Shawn Guo <shawnguo@...nel.org>, UNGLinuxDriver@...rochip.com,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH net-next 0/9] net: pcs: Add support for devices
 probed in the "usual" manner

Hi Sean,

On Mon, Jul 11, 2022 at 12:05:10PM -0400, Sean Anderson wrote:
> For a long time, PCSs have been tightly coupled with their MACs. For
> this reason, the MAC creates the "phy" or mdio device, and then passes
> it to the PCS to initialize. This has a few disadvantages:
> 
> - Each MAC must re-implement the same steps to look up/create a PCS
> - The PCS cannot use functions tied to device lifetime, such as devm_*.
> - Generally, the PCS does not have easy access to its device tree node
> 
> I'm not sure if these are terribly large disadvantages. In fact, I'm not
> sure if this series provides any benefit which could not be achieved
> with judicious use of helper functions. In any case, here it is.
> 
> NB: Several (later) patches in this series should not be applied. See
> the notes in each commit for details on when they can be applied.

Sorry to burst your bubble, but the networking drivers on NXP LS1028A
(device tree at arch/arm64/boot/dts/freescale/fsl-ls1028a.dtsi, drivers
at drivers/net/ethernet/freescale/enetc/ and drivers/net/dsa/ocelot/)
do not use the Lynx PCS through a pcs-handle, because the Lynx PCS in
fact has no backing OF node there, nor do the internal MDIO buses of the
ENETC and of the switch.

It seems that I need to point this out explicitly: you need to provide
at least a working migration path to your PCS driver model. Currently
there isn't one, and as a result, networking is broken on the LS1028A
with this patch set.