netdev - Re: Issue with RTL8111 NIC after upgrade to kernel 4.19

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Message-ID: <CAB9dFdvw8QqzaVYV3bOMGtACyvqWnE9uy96m1tu2C+jjzQR9_Q@mail.gmail.com>
Date:   Wed, 21 Nov 2018 17:53:46 -0400
From:   Marc Dionne <marc.c.dionne@...il.com>
To:     hkallweit1@...il.com
Cc:     andrew@...n.ch, norbert.jurkeit@....de, nic_swsd@...ltek.com,
        Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        michael.wiktowy@...il.com, jcline@...hat.com
Subject: Re: Issue with RTL8111 NIC after upgrade to kernel 4.19

On Wed, Nov 21, 2018 at 4:52 PM Heiner Kallweit <hkallweit1@...il.com> wrote:
>
> On 21.11.2018 21:49, Heiner Kallweit wrote:
> > On 21.11.2018 21:32, Heiner Kallweit wrote:
> >> On 21.11.2018 21:20, Andrew Lunn wrote:
> >>>> request_module() is supposed to be synchronous, however after some
> >>>> reading this may not be 100% guaranteed. Maybe the module init
> >>>> function on some systems isn't finished yet when request_module()
> >>>> returns. As a result the genphy driver may be used instead of
> >>>> the PHY version-specific driver.
> >>>
> >>> Hi Heiner
> >>>
> >>> That would be true for all PHYs i think. We would of noticed this
> >>> problem with other systems using other PHY drivers.
> >>>
> >>>     Andrew
> >>>
> >> It could be a timing issue affecting certain systems only. At least
> >> for now I don't have a good explanation why loading the module via
> >> request_module() and loading it upfront manually makes a difference.
> >>
> >> One affected user just reported the PHY to be a RTL8211B. This is
> >> what I expected, because this PHY crashes when writing to the MMD
> >> registers (the MMD registers are used otherwise by this PHY).
> >> See also commit 0231b1a074c6 ("net: phy: realtek: Use the dummy
> >> stubs for MMD register access for rtl8211b").
> >>
> >> Let's see whether the other affected systems use the same PHY
> >> version.
> >>
> > Next report is also about a RTL8211B and as I assumed:
> > - W/o manually loading the realtek module the genphy driver is used
> >   and network fails.
> > - W/ manually loading the realtek module the proper RTL8211B PHY
> >   driver is used and network works.
> >
> > So it seems that even after request_module() the PHY driver isn't
> > yet available when device and driver are matched.
> >
> > If further reports support this (pre-)analysis, then indeed it
> > seems to be a timing issue and a proper fix most likely is
> > difficult. As a workaround I could imagine to add a delay loop
> > after request_module() checking for a Realtek PHY driver via
> > driver_find(). When adding one small delay after this we should
> > be sufficiently sure that all Realtek PHY drivers are registered.
> >
> Uups, no. We talk about phylib here, not about the r8169 driver.
> So we need a different solution.
>
> >> Heiner

Thanks for the explanation, better than my crude attempt at
understanding what was going on.

If you have any proposed fixes or diagnostic patches based on current
mainline I can quickly compile and test them here on an affected
system.  It doesn't fail consistently for me (as others have
reported), but that could be because it depends on the timing.

Marc