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

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Date:   Mon, 16 Jan 2023 08:35:46 +0100
From:   Alexander Stein <alexander.stein@...tq-group.com>
To:     Andrew Lunn <andrew@...n.ch>,
        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

Hi,

Am Sonntag, 15. Januar 2023, 23:23:51 CET schrieb Pierluigi Passaro:
> 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.

Not in every case though. On i.MX6UL has the following memory map for FEC:
* FEC2: 0x020b4000
* FEC1: 0x02188000

Which essentially means that fec2 will be probed first.

> The EPROBE_DEFER does not prevent the second instance from being probed.
> This is the origin of the problem.

Is this the actual cause? There is also a problem in the case above if the 
MDIO controlling interface (fec2) is not probed first, e.g. using fec1 for 
MDIO access. But then again there is i.MX6ULG1 which only has fec1 
interface...

Best regards,
Alexander