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Date:   Mon, 16 Jan 2023 16:32:21 +0100
From:   Andrew Lunn <andrew@lunn.ch>
To:     Pierluigi Passaro <pierluigi.p@variscite.com>
Cc:     Pierluigi Passaro <pierluigi.passaro@gmail.com>,
        "wei.fang@nxp.com" <wei.fang@nxp.com>,
        "shenwei.wang@nxp.com" <shenwei.wang@nxp.com>,
        "xiaoning.wang@nxp.com" <xiaoning.wang@nxp.com>,
        "linux-imx@nxp.com" <linux-imx@nxp.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "edumazet@google.com" <edumazet@google.com>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "pabeni@redhat.com" <pabeni@redhat.com>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        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
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> 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.

> - FEC0 is successfully probed, but MDIO bus is now assigned to FEC1
>   and cannot? and no communication takes place

       Andrew