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From:   Pierluigi Passaro <pierluigi.p@variscite.com>
To:     Andrew Lunn <andrew@lunn.ch>
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        Eran Matityahu <eran.m@variscite.com>,
        Nate Drude <Nate.D@variscite.com>,
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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/I0G8u4g9Yr5d7K6gBiKAgAAHoYCAABs7gIAAlBIcgABwD4CAAFCj3Q==
Date:   Mon, 16 Jan 2023 20:23:29 +0000
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On Mon, Jan 16, 2023 at 4:32 PM Andrew Lunn <andrew@lunn.ch> wrote:=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" GP=
IO=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=
_DEFERRED=0A=
> > - FEC1 is successfully probed: being the MDIO bus still not owned, the =
driver assume=0A=
> > =A0 that the ownership must be assigned to the 1st one successfully pro=
bed, but no=0A=
> > =A0 MDIO node is actually present and no communication takes place.=0A=
>=0A=
> So semantics of a phandle is that you expect what it points to, to=0A=
> exists. So if phy-handle points to a PHY, when you follow that pointer=0A=
> and find it missing, you should defer the probe. So this step should=0A=
> not succeed.=0A=
>=0A=
I agree with you: the check is present, but the current logic is not consis=
tent.=0A=
Whenever the node owning the MDIO fails the probe due to EPROBE_DEFERRED,=
=0A=
also the second node must defer the probe, otherwise no MDIO communication=
=0A=
is possible.=0A=
That's why the patch set the static variable wait_for_mdio_bus=A0to track t=
he status.=0A=
>=0A=
> > - FEC0 is successfully probed, but MDIO bus is now assigned to FEC1=0A=
> > =A0 and cannot =A0and no communication takes place=0A=
>=0A=
> =A0 =A0 =A0 =A0Andrew=