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: <2d028102-dd6a-c9f6-9e18-5abf84eb37a1@seco.com>
Date:   Tue, 19 Jul 2022 11:46:23 -0400
From:   Sean Anderson <sean.anderson@...o.com>
To:     Vladimir Oltean <olteanv@...il.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



On 7/19/22 11:38 AM, Vladimir Oltean wrote:
> On Tue, Jul 19, 2022 at 11:28:42AM -0400, Sean Anderson wrote:
>> Hi Vladimir,
>> 
>> On 7/19/22 11:25 AM, Vladimir Oltean wrote:
>> > 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.
>> > 
>> 
>> Please refer to patches 4, 5, and 6.
> 
> I don't understand, could you be more clear? Are you saying that I
> shouldn't have applied patch 9 while testing? When would be a good
> moment to apply patch 9?

I'm saying that patches 4 and 5 [1] provide "...a working migration
path to [my] PCS driver model." Since enetc/ocelot do not use
devicetree for the PCS, patch 9 should have no effect.

That said, if you've tested this on actual hardware, I'm interested
in your results. I do not have access to enetc/ocelot hardware, so
I was unable to test whether my proposed migration would work.

--Sean

[1] I listed 6 but it seems like it just has some small hunks which should have been in 5 instead