netdev - Re: [PATCH v2] net: fec: manage corner deferred probe condition

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Message-ID: <Y8STz5eOoSPfkMbU@lunn.ch>
Date:   Mon, 16 Jan 2023 01:01:19 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Pierluigi Passaro <pierluigi.passaro@...il.com>
Cc:     Pierluigi Passaro <pierluigi.p@...iscite.com>, wei.fang@....com,
        shenwei.wang@....com, xiaoning.wang@....com, linux-imx@....com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, eran.m@...iscite.com,
        nate.d@...iscite.com, francesco.f@...iscite.com
Subject: Re: [PATCH v2] net: fec: manage corner deferred probe condition

On Sun, Jan 15, 2023 at 11:23:51PM +0100, Pierluigi Passaro wrote:
> On Sun, Jan 15, 2023 at 10:56 PM Andrew Lunn <andrew@...n.ch> wrote:
> > On Sun, Jan 15, 2023 at 10:38:04PM +0100, Pierluigi Passaro wrote:
> > > For dual fec interfaces, external phys can only be configured by fec0.
> > > When the function of_mdiobus_register return -EPROBE_DEFER, the driver
> > > is lately called to manage fec1, which wrongly register its mii_bus as
> > > fec0_mii_bus.
> > > When fec0 retry the probe, the previous assignement prevent the MDIO bus
> > > registration.
> > > Use a static boolean to trace the orginal MDIO bus deferred probe and
> > > prevent further registrations until the fec0 registration completed
> > > succesfully.
> >
> > The real problem here seems to be that fep->dev_id is not
> > deterministic. I think a better fix would be to make the mdio bus name
> > deterministic. Use pdev->id instead of fep->dev_id + 1. That is what
> > most mdiobus drivers use.
> >
> Actually, the sequence is deterministic, fec0 and then fec1,
> but sometimes the GPIO of fec0 is not yet available.
> The EPROBE_DEFER does not prevent the second instance from being probed.
> This is the origin of the problem.

Maybe i understood you wrongly, but it sounds like the second instance
takes the name space of the first? And when the first probes for the
second time, the name space is taken and the registration fails? To
me, this is indeterminate behaviour, the name fec0_mii_bus is not
determinate.

	Andrew