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

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Date:   Mon, 16 Jan 2023 20:23:29 +0000
From:   Pierluigi Passaro <pierluigi.p@...iscite.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     Pierluigi Passaro <pierluigi.passaro@...il.com>,
        "wei.fang@....com" <wei.fang@....com>,
        "shenwei.wang@....com" <shenwei.wang@....com>,
        "xiaoning.wang@....com" <xiaoning.wang@....com>,
        "linux-imx@....com" <linux-imx@....com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Eran Matityahu <eran.m@...iscite.com>,
        Nate Drude <Nate.D@...iscite.com>,
        Francesco Ferraro <francesco.f@...iscite.com>
Subject: Re: [PATCH v2] net: fec: manage corner deferred probe condition

On Mon, Jan 16, 2023 at 4:32 PM Andrew Lunn <andrew@...n.ch> wrote:
> > This is the setup of the corner case:
> > - FEC0 is the owner of MDIO bus, but its own PHY rely on a "delayed" GPIO
> > - FEC1 rely on FEC0 for MDIO communications
> > The sequence is something like this
> > - FEC0 probe start, but being the reset GPIO "delayed" it return EPROBE_DEFERRED
> > - FEC1 is successfully probed: being the MDIO bus still not owned, the driver assume
> >   that the ownership must be assigned to the 1st one successfully probed, but no
> >   MDIO node is actually present and no communication takes place.
>
> So semantics of a phandle is that you expect what it points to, to
> exists. So if phy-handle points to a PHY, when you follow that pointer
> and find it missing, you should defer the probe. So this step should
> not succeed.
>
I agree with you: the check is present, but the current logic is not consistent.
Whenever the node owning the MDIO fails the probe due to EPROBE_DEFERRED,
also the second node must defer the probe, otherwise no MDIO communication
is possible.
That's why the patch set the static variable wait_for_mdio_bus to track the status.
>
> > - FEC0 is successfully probed, but MDIO bus is now assigned to FEC1
> >   and cannot  and no communication takes place
>
>        Andrew