Re: [PATCH net] net: mdio: Prevent Clause 45 scan on SMSC PHYs

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Tue, Jan 02, 2024 at 02:42:17PM +0100, Andrew Lunn wrote:
> On Mon, Jan 01, 2024 at 11:44:38PM +0100, Heiner Kallweit wrote:
> > On 01.01.2024 22:31, Ezra Buehler wrote:
> > > Since commit 1a136ca2e089 ("net: mdio: scan bus based on bus
> > > capabilities for C22 and C45") our AT91SAM9G25-based GARDENA smart
> > > Gateway will no longer boot.
> > > 
> > > Prior to the mentioned change, probe_capabilities would be set to
> > > MDIOBUS_NO_CAP (0) and therefore, no Clause 45 scan was performed.
> > > Running a Clause 45 scan on an SMSC/Microchip LAN8720A PHY will (at
> > > least with our setup) considerably slow down kernel startup and
> > > ultimately result in a board reset.
> > > 
> > > AFAICT all SMSC/Microchip PHYs are Clause 22 devices. Some have a
> > > "Clause 45 protection" feature (e.g. LAN8830) and others like the
> > > LAN8804 will explicitly state the following in the datasheet:
> > > 
> > >     This device may respond to Clause 45 accesses and so must not be
> > >     mixed with Clause 45 devices on the same MDIO bus.
> > > 
> > 
> > I'm not convinced that some heuristic based on vendors is a
> > sustainable approach. Also I'd like to avoid (as far as possible)
> > that core code includes vendor driver headers. Maybe we could use
> > a new PHY driver flag. Approaches I could think of:
> 
> We already have a core hack for these broken PHYs:

Yes, and it is this very function that the patch at the start of this
thread is changing!

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