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Date:   Tue, 3 Jan 2023 17:56:33 +0200
From:   Vladimir Oltean <olteanv@gmail.com>
To:     Andrew Lunn <andrew@lunn.ch>
Cc:     Michael Walle <michael@walle.cc>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Jose Abreu <Jose.Abreu@synopsys.com>,
        Sergey Shtylyov <s.shtylyov@omp.ru>,
        Wei Fang <wei.fang@nxp.com>,
        Shenwei Wang <shenwei.wang@nxp.com>,
        Clark Wang <xiaoning.wang@nxp.com>,
        NXP Linux Team <linux-imx@nxp.com>,
        Sean Wang <sean.wang@mediatek.com>,
        Landen Chao <Landen.Chao@mediatek.com>,
        DENG Qingfang <dqfext@gmail.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-renesas-soc@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Luiz Angelo Daros de Luca <luizluca@gmail.com>
Subject: Re: [PATCH RFC net-next v2 11/12] net: dsa: Separate C22 and C45
 MDIO bus transaction methods
Message-ID: <20230103155633.tfdxncl75s4tb2ln@skbuf>
References: <20221227-v6-2-rc1-c45-seperation-v2-0-ddb37710e5a7@walle.cc>
 <20221227-v6-2-rc1-c45-seperation-v2-0-ddb37710e5a7@walle.cc>
 <20221227-v6-2-rc1-c45-seperation-v2-11-ddb37710e5a7@walle.cc>
 <20221227-v6-2-rc1-c45-seperation-v2-11-ddb37710e5a7@walle.cc>
 <20230103153134.utalc6kw3l34dp4s@skbuf>
 <Y7ROa8ql9R5SHPsK@lunn.ch>
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On Tue, Jan 03, 2023 at 04:48:59PM +0100, Andrew Lunn wrote:
> > 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.

Actually I believe that in v1 you did extend ds->ops with C45 methods,
but it's me who told you to remove them:
https://patchwork.kernel.org/project/netdevbpf/patch/20220508153049.427227-10-andrew@lunn.ch/#24852813

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

And rightfully so. IMHO, letting DSA allocate ds->slave_mii_bus out of
driver writer sheer convenience (a secondary purpose) should be deprecated,
unless the reason for using ds->slave_mii_bus is the lack of a phy-handle
(the primary purpose). It becomes that more confusing to have to extend
dsa_switch_ops with 2 more methods which serve the secondary purpose but
not the primary one.

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

I sent a private email to Luiz a few minutes ago asking him to confirm.