netdev - Re: [PATCH net-next] ARM: dts: imx6qdl: Remove unnecessary mdio #address-cells/#size-cells

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Date:   Fri, 23 Jul 2021 16:35:56 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Fabio Estevam <festevam@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Shawn Guo <shawnguo@...nel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Joakim Zhang <qiangqing.zhang@....com>,
        Rob Herring <robh+dt@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH net-next] ARM: dts: imx6qdl: Remove unnecessary mdio
 #address-cells/#size-cells

On Fri, Jul 23, 2021 at 10:15:52AM -0300, Fabio Estevam wrote:
> Hi Vladimr,
> 
> On Fri, Jul 23, 2021 at 10:08 AM Vladimir Oltean <olteanv@...il.com> wrote:
> 
> > Are you actually sure this is the correct fix? If I look at mdio.yaml, I
> > think it is pretty clear that the "ethernet-phy" subnode of the MDIO
> > controller must have an "@[0-9a-f]+$" pattern, and a "reg" property. If
> > it did, then it wouldn't warn about #address-cells.
> 
> Thanks for reviewing it.
> 
> After double-checking I realize that the correct fix would be to pass
> the phy address, like:
> 
> phy: ethernet-phy@1 {
> reg = <1>;
> 
> Since the Ethernet PHY address is design dependant, I can not make the
> fix myself.
> 
> I will try to ping the board maintainers for passing the correct phy address.
> 
> Thanks

Normally you should have been able to make all PHY addresses be 0. That
is the MDIO "broadcast address" and if there's a single PHY on the bus,
it should respond to that.

Citation:

IEEE 802.3-2015:

22.2.4.5.5 PHYAD (PHY Address)

The PHY Address is five bits, allowing 32 unique PHY addresses. The first PHY address bit transmitted and
received is the MSB of the address. A PHY that is connected to the station management entity via the
mechanical interface defined in 22.6 shall always respond to transactions addressed to PHY Address zero
<00000>. A station management entity that is attached to multiple PHYs must have prior knowledge of the
appropriate PHY Address for each PHY.

However, if you google "MDIO broadcast address", you'll find all sorts
of funny reports of buggy PHYs not adhering to that clause, under all
sorts of pretexts...