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

From: Vladimir Oltean <olteanv@gmail.com>
To: Sean Anderson <sean.anderson@seco.com>
Cc: Heiner Kallweit <hkallweit1@gmail.com>,
	Russell King <linux@armlinux.org.uk>,
	netdev@vger.kernel.org, Jakub Kicinski <kuba@kernel.org>,
	Madalin Bucur <madalin.bucur@nxp.com>,
	"David S . Miller" <davem@davemloft.net>,
	Paolo Abeni <pabeni@redhat.com>,
	Ioana Ciornei <ioana.ciornei@nxp.com>,
	linux-kernel@vger.kernel.org, Eric Dumazet <edumazet@google.com>,
	Andrew Lunn <andrew@lunn.ch>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Claudiu Manoil <claudiu.manoil@nxp.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Frank Rowand <frowand.list@gmail.com>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Li Yang <leoyang.li@nxp.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Paul Mackerras <paulus@samba.org>,
	Rob Herring <robh+dt@kernel.org>,
	Saravana Kannan <saravanak@google.com>,
	Shawn Guo <shawnguo@kernel.org>,
	UNGLinuxDriver@microchip.com,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Vladimir Oltean <vladimir.oltean@nxp.com>,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [RFC PATCH net-next 0/9] net: pcs: Add support for devices probed in the "usual" manner
Date: Tue, 19 Jul 2022 18:25:39 +0300	[thread overview]
Message-ID: <20220719152539.i43kdp7nolbp2vnp@skbuf> (raw)
In-Reply-To: <20220711160519.741990-1-sean.anderson@seco.com>

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.