netdev - Re: [PATCH v1 1/3] net: phy: Allow mdio buses to auto-probe c45 devices

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Message-ID: <20200617185120.GB240559@lunn.ch>
Date:   Wed, 17 Jun 2020 20:51:20 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Calvin Johnson <calvin.johnson@....nxp.com>,
        Jeremy Linton <jeremy.linton@....com>, Jon <jon@...id-run.com>,
        Cristi Sovaiala <cristian.sovaiala@....com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        netdev@...r.kernel.org, linux.cj@...il.com
Subject: Re: [PATCH v1 1/3] net: phy: Allow mdio buses to auto-probe c45
 devices

> > +	/* bus capabilities, used for probing */
> > +	enum {
> > +		MDIOBUS_C22 = 0,
> > +		MDIOBUS_C45,
> > +		MDIOBUS_C22_C45,
> > +	} probe_capabilities;
> 
> I think it would be better to reserve "0" to mean that no capabilities
> have been declared.  We hae the situation where we have mii_bus that
> exist which do support C45, but as they stand, probe_capabilities will
> be zero, and with your definitions above, that means MDIOBUS_C22.
> 
> It seems this could lock in some potential issues later down the line
> if we want to use this elsewhere.

Hi Russell

Actually, this patch already causes issues, i think.

drivers/net/ethernet/marvell/mvmdio.c contains two MDIO bus master
drivers. "marvell,orion-mdio" is C22 only. "marvell,xmdio" is C45
only. Because the capabilites is not initialized, it will default to
0, aka MDIOBUS_C22, for the C45 only bus master, and i expect bad
things will happen.

We need the value of 0 to cause existing behaviour. Or all MDIO bus
drivers need reviewing, and the correct capabilities set.

   Andrew