netdev - Re: [PATCH RFC net-next v2 11/12] net: dsa: Separate C22 and C45 MDIO bus transaction methods

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Date:   Tue, 3 Jan 2023 16:48:59 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Michael Walle <michael@...le.cc>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        Sergey Shtylyov <s.shtylyov@....ru>,
        Wei Fang <wei.fang@....com>,
        Shenwei Wang <shenwei.wang@....com>,
        Clark Wang <xiaoning.wang@....com>,
        NXP Linux Team <linux-imx@....com>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH RFC net-next v2 11/12] net: dsa: Separate C22 and C45
 MDIO bus transaction methods

> Since clause 45 PHYs are identified by the "ethernet-phy-ieee802.3-c45"
> compatible string (otherwise they are C22), then a PHY which is not
> described in the device tree can only be C22. So this is why
> ds->slave_mii_bus only deals with clause 22 methods, and the true reason
> behind the comment above.
> 
> But actually this premise is no longer true since Luiz' commit
> fe7324b93222 ("net: dsa: OF-ware slave_mii_bus"), which introduced the
> strange concept of an "OF-aware helper for internal PHYs which are not
> described in the device tree". After his patch, it is possible to have
> something like this:
> 
> 	ethernet-switch {
> 		ethernet-ports {
> 			port@1 {
> 				reg = <1>;
> 			};
> 		};
> 
> 		mdio {
> 			ethernet-phy@1 {
> 				compatible = "ethernet-phy-ieee802.3-c45"
> 				reg = <1>;
> 			};
> 		};
> 	};
> 
> As you can see, this is a clause 45 internal PHY which lacks a
> phy-handle, so its bus must be put in ds->slave_mii_bus in order for
> dsa_slave_phy_connect() to see it without that phy-handle (based on the
> port number matching with the PHY number). After Luiz' patch, this kind
> of device tree is possible, and it invalidates the assumption about
> ds->slave_mii_bus only driving C22 PHYs.

My memory is hazy, but i think at the time i wrote these patches,
there was no DSA driver which made use of ds->slave_mii_bus with
C45. So i took the short cut of only supporting C22.

Those DSA drivers which do support C45 all register their bus directly
with the MDIO core.

So Luiz patches may allow a C45 bus, but are there any drivers today
actually using it?

	 Andrew