linux-kernel - Re: [RFC net-next] of: mdio: Honor hints from MDIO bus drivers

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Message-ID: <20170411231424.GA6174@lunn.ch>
Date:   Wed, 12 Apr 2017 01:14:24 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC net-next] of: mdio: Honor hints from MDIO bus drivers

> To give some more background and rational for this change.
> 
> On a platform where we have a parent MDIO bus, backed by the
> mdio-bcm-unimac.c driver, we also register a slave MII bus (through
> net/dsa/dsa2.c) which is parented to this UniMAC MDIO bus through an
> assignment of of_node. This slave MII bus is created in order to
> intercept reads/writes to problematic addresses (e.g: that clashes with
> another piece of hardware).
> 
> This means that the slave DSA MII bus inherits all child nodes from the
> originating master MII bus. This also means that when the slave MII bus
> is probed via of_mdiobus_register(), we probe the same devices twice:
> once through the master, another time through the slave.

Ah, O.K. This makes more sense. On the hardware i have, we get three
deep in MDIO busses. We have the FEC mdio bus. On top of that we have
a gpio-mux-mdio, and on top of that we have the mv88e6xxx mdio
bus. And i've never seen issues.

So your real problem here is you have two mdio busses using the same
device tree properties. I would actually say that is just plain
broken.

	Andrew