netdev - Re: [PATCH net] net: phy: replace preliminary fix for PHY driver sometimes not binding to the device

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Date:   Fri, 28 Dec 2018 22:56:47 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     andrew@...n.ch, f.fainelli@...il.com, gregkh@...uxfoundation.org,
        rafael@...nel.org, netdev@...r.kernel.org, norbert.jurkeit@....de,
        frank@...wford.emu.id.au
Subject: Re: [PATCH net] net: phy: replace preliminary fix for PHY driver
 sometimes not binding to the device

On 28.12.2018 22:02, David Miller wrote:
> From: Heiner Kallweit <hkallweit1@...il.com>
> Date: Mon, 24 Dec 2018 12:21:12 +0100
> 
>> phy_device_create() uses request_module() to load the PHY driver module
>> based on the PHY ID of the device. There is some timing issue which
>> sometimes prevents the PHY driver to bind to the device. In such cases
>> the genphy driver is used what can cause problems if genphy isn't
>> compatible with the respective PHY.
>> It turned out that the first fix can fix the issue in some but not all
>> cases. Moving the call to device_initialize() before the call to
>> request_module() was reported to fix the issue.
>> I can't explain where the root cause of the issue is and why this fix
>> works. AFAICS device_initialize() just initializes the device struct
>> w/o doing anything that could interfere with e.g. bus_add_driver().
>> This patch removes the first preliminary fix attempt.
>>
>> Reference:
>> https://bugzilla.redhat.com/show_bug.cgi?id=1650984
>>
>> Fixes: c85ddecae6e5 ("net: phy: add workaround for issue where PHY driver doesn't bind to the device")
>> Tested-by: Norbert Jurkeit <norbert.jurkeit@....de>
>> Tested-by: Frank Crawford <frank@...wford.emu.id.au>
>> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> 
> I can't see any way this can make a difference.  I'm really stumped
> and even if it did fix all of the issues people are seeing I wouldn't
> want to apply this patch.
> 
> We need to know why, and put the why into the commit log message.
> 
> Thanks.
> 
IIRC I sent a mail to you already asking not to apply the patch because
again I had users complaining that the fix doesn't work for them.
Root cause seems to be a tricky race in the drive base core, therefore
I included Greg and Rafael. Due to this race even small code changes
which doesn't make sense from a functional perspective help for
few users.

I can't reproduce the issue on my systems, therefore I requested more
debug info from requested users. Once I have more input I'll go on
with the root cause analysis.