linux-kernel - Re: [PATCH net-next 06/16] net: pcs: xpcs: Avoid creating dummy XPCS MDIO device

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Message-ID: <ZW840qQMbVRto442@shell.armlinux.org.uk>
Date:   Tue, 5 Dec 2023 14:50:58 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Serge Semin <fancer.lancer@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Jose Abreu <Jose.Abreu@...opsys.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Tomer Maimon <tmaimon77@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, openbmc@...ts.ozlabs.org,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 06/16] net: pcs: xpcs: Avoid creating dummy XPCS
 MDIO device

On Tue, Dec 05, 2023 at 02:52:24PM +0100, Andrew Lunn wrote:
> On Tue, Dec 05, 2023 at 02:31:41PM +0300, Serge Semin wrote:
> > On Tue, Dec 05, 2023 at 10:49:47AM +0000, Russell King (Oracle) wrote:
> > > On Tue, Dec 05, 2023 at 01:35:27PM +0300, Serge Semin wrote:
> > > > If the DW XPCS MDIO devices are either left unmasked for being auto-probed
> > > > or explicitly registered in the MDIO subsystem by means of the
> > > > mdiobus_register_board_info() method there is no point in creating the
> > > > dummy MDIO device instance in order to get the DW XPCS handler since the
> > > > MDIO core subsystem will create the device during the MDIO bus
> > > > registration procedure.
> > > 
> > 
> > > Please reword this overly long sentence.
> > 
> > Ok.
> > 
> > > 
> > > If they're left unmasked, what prevents them being created as PHY
> > > devices?
> > 
> > Not sure I fully get what you meant. If they are left unmasked the
> > MDIO-device descriptor will be created by the MDIO subsystem anyway.
> > What the point in creating another one?
> 
> Saying what Russell said, in a different way:
> 
> /*
>  * Return true if the child node is for a phy. It must either:
>  * o Compatible string of "ethernet-phy-idX.X"
>  * o Compatible string of "ethernet-phy-ieee802.3-c45"
>  * o Compatible string of "ethernet-phy-ieee802.3-c22"
>  * o In the white list above (and issue a warning)
>  * o No compatibility string
>  *
>  * A device which is not a phy is expected to have a compatible string
>  * indicating what sort of device it is.
>  */
> bool of_mdiobus_child_is_phy(struct device_node *child)
> 
> So when walking the bus, if a node is found which fits these criteria,
> its assumed to be a PHY. 
> 
> Anything on the MDIO bus which is not a PHY needs to use a compatible.

Right. I'd actually forgotten about the firmware-based walking, and
was thinking more of the non-firmware bus scanning as the commit
message was talking about being _unmasked_ and the only mask we have
is bus->phy_mask.

It seems to me that this is yet another case of a really confusing
commit message making review harder than it needs to be.

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