linux-kernel - Re: [PATCH net-next 0/5] net: phy: C45-over-C22 access

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Date:   Wed, 25 Jan 2023 14:52:43 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Michael Walle <michael@...le.cc>
Cc:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        Yisen Zhuang <yisen.zhuang@...wei.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Marek Behún <kabel@...nel.org>,
        Xu Liang <lxu@...linear.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 0/5] net: phy: C45-over-C22 access

On Tue, Jan 24, 2023 at 10:20:33PM +0100, Michael Walle wrote:
> Am 2023-01-24 22:03, schrieb Andrew Lunn:
> > > Btw. for the DT case, it seems we need yet another property
> > > to indicate broken MDIO busses.
> > 
> > I would prefer to avoid that. I would suggest you do what i did for
> > the none DT case. First probe using C22 for all devices known in DT.
> > Then call mdiobus_prevent_c45_scan() which will determine if any of
> > the found devices are FUBAR and will break C45. Then do a second probe
> > using C45 and/or C45 over C22 for those devices in DT with the c45
> > compatible.
> 
> I tried that yesterday. Have a look at of_mdiobus_register() [1].
> There the device tree is walked and each PHY with a reg property
> is probed. Afterwards, if there was a node without a reg property,
> the bus is scanned for the missing PHYs. If we would just probe c22
> first, the order of the auto scanning might change, if there is a
> c45 phy in between two c22 phys. I was thinking to just ignore the
> case that the autoscan would discover a broken PHY.

I think it is pretty rare to not have a reg value. The DT lint tools
will complain about that, etc. So any examples are likely to be old
boards. And old board are a lot less likely to have C45 PHYs. So there
is a corner case left unhandled, but it seems pretty unlikely. So i
agree, lets address it if anybody reports issues. But please mention
it in the commit message, just i can somebody does a git bisect, etc.

   Andrew