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

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Message-ID: <7d6362e1-e197-d338-d6b0-9036c3802e2c@gmail.com>
Date:   Wed, 21 Nov 2018 21:52:17 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Norbert Jurkeit <norbert.jurkeit@....de>, nic_swsd@...ltek.com,
        Florian Fainelli <f.fainelli@...il.com>, davem@...emloft.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        michael.wiktowy@...il.com, jcline@...hat.com,
        marc.c.dionne@...il.com
Subject: Re: Issue with RTL8111 NIC after upgrade to kernel 4.19

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
>>
>