Date:   Wed, 21 Nov 2018 23:28:21 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Marc Dionne <marc.c.dionne@...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 21.11.2018 22:53, Marc Dionne wrote:
> 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.
> 

Thanks for the offer. Can you try the following diagnostic patch
and check whether it helps?

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 55202a0ac..84f417f8b 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -607,6 +607,8 @@ struct phy_device *phy_device_create(struct mii_bus *bus, int addr, int phy_id,
         */
        request_module(MDIO_MODULE_PREFIX MDIO_ID_FMT, MDIO_ID_ARGS(phy_id));

+       msleep(1000);
+
        device_initialize(&mdiodev->dev);

        return dev;


> Marc
> 

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