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From:   Pierluigi Passaro <pierluigi.p@variscite.com>
To:     Andrew Lunn <andrew@lunn.ch>,
        Pierluigi Passaro <pierluigi.passaro@gmail.com>
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        Eran Matityahu <eran.m@variscite.com>,
        Nate Drude <Nate.D@variscite.com>,
        Francesco Ferraro <francesco.f@variscite.com>
Subject: Re: [PATCH v2] net: fec: manage corner deferred probe condition
Thread-Topic: [PATCH v2] net: fec: manage corner deferred probe condition
Thread-Index: AQHZKSmr1PIgZgy/I0G8u4g9Yr5d7K6gBiKAgAAHoYCAABs7gIAAlBIc
Date:   Mon, 16 Jan 2023 08:51:44 +0000
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References: <20230115213804.26650-1-pierluigi.p@variscite.com>
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On Mon, Jan 16, 2023 at 1:01 AM Andrew Lunn <andrew@lunn.ch> wrote:=0A=
> On Sun, Jan 15, 2023 at 11:23:51PM +0100, Pierluigi Passaro wrote:=0A=
> > On Sun, Jan 15, 2023 at 10:56 PM Andrew Lunn <andrew@lunn.ch> wrote:=0A=
> > > On Sun, Jan 15, 2023 at 10:38:04PM +0100, Pierluigi Passaro wrote:=0A=
> > > > For dual fec interfaces, external phys can only be configured by fe=
c0.=0A=
> > > > When the function of_mdiobus_register return -EPROBE_DEFER, the dri=
ver=0A=
> > > > is lately called to manage fec1, which wrongly register its mii_bus=
 as=0A=
> > > > fec0_mii_bus.=0A=
> > > > When fec0 retry the probe, the previous assignement prevent the MDI=
O bus=0A=
> > > > registration.=0A=
> > > > Use a static boolean to trace the orginal MDIO bus deferred probe a=
nd=0A=
> > > > prevent further registrations until the fec0 registration completed=
=0A=
> > > > succesfully.=0A=
> > >=0A=
> > > The real problem here seems to be that fep->dev_id is not=0A=
> > > deterministic. I think a better fix would be to make the mdio bus nam=
e=0A=
> > > deterministic. Use pdev->id instead of fep->dev_id + 1. That is what=
=0A=
> > > most mdiobus drivers use.=0A=
> > >=0A=
> > Actually, the sequence is deterministic, fec0 and then fec1,=0A=
> > but sometimes the GPIO of fec0 is not yet available.=0A=
> > The EPROBE_DEFER does not prevent the second instance from being probed=
.=0A=
> > This is the origin of the problem.=0A=
>=0A=
> Maybe I understood you wrongly, but it sounds like the second instance=0A=
> takes the namespace of the first? And when the first probes for the=0A=
> second time, the name space is taken and the registration fails? To=0A=
> me, this is indeterminate behaviour, the name fec0_mii_bus is not=0A=
> determinate.=0A=
>=0A=
> =A0 =A0 =A0 =A0 Andrew=0A=
This is the setup of the corner case:=0A=
- FEC0 is the owner of MDIO bus, but its own PHY rely on a "delayed" GPIO=
=0A=
- FEC1 rely on FEC0 for MDIO communications=0A=
The sequence is something like this=0A=
- FEC0 probe start, but being the reset GPIO "delayed" it return EPROBE_DEF=
ERRED=0A=
- FEC1 is successfully probed: being the MDIO bus still not owned, the driv=
er assume=0A=
=A0 that the ownership must be assigned to the 1st one successfully probed,=
 but no=0A=
=A0 MDIO node is actually present and no communication takes place.=0A=
- FEC0 is successfully probed, but MDIO bus is now assigned to FEC1 and can=
not=A0 and no communication takes place=