linux-kernel - Re: [Intel-wired-lan] [PATCH v2 2/2] e1000e: fix link fluctuations problem

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Date: Thu, 9 May 2024 12:13:27 +0300
From: "Ruinskiy, Dima" <dima.ruinskiy@...el.com>
To: Sasha Neftin <sasha.neftin@...el.com>, Andrew Lunn <andrew@...n.ch>, Ricky
 Wu <en-wei.wu@...onical.com>
CC: <netdev@...r.kernel.org>, <rickywu0421@...il.com>,
	<linux-kernel@...r.kernel.org>, <edumazet@...gle.com>,
	<intel-wired-lan@...ts.osuosl.org>, <kuba@...nel.org>,
	<anthony.l.nguyen@...el.com>, <pabeni@...hat.com>, <davem@...emloft.net>,
	"Lifshits, Vitaly" <vitaly.lifshits@...el.com>, naamax.meir
	<naamax.meir@...ux.intel.com>, "Avivi, Amir" <amir.avivi@...el.com>, "Keller,
 Jacob E" <jacob.e.keller@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH v2 2/2] e1000e: fix link fluctuations
 problem

On 08/05/2024 8:05, Sasha Neftin wrote:
> On 07/05/2024 15:31, Andrew Lunn wrote:
>> On Fri, May 03, 2024 at 06:18:36PM +0800, Ricky Wu wrote:
>>> As described in https://bugzilla.kernel.org/show_bug.cgi?id=218642,
>>> Intel I219-LM reports link up -> link down -> link up after hot-plugging
>>> the Ethernet cable.
>>
>> Please could you quote some parts of 802.3 which state this is a
>> problem. How is this breaking the standard.
>>
>>     Andrew
> 
> In I219-* parts used LSI PHY. This PHY is compliant with the 802.3 IEEE 
> standard if I recall correctly. Auto-negotiation and link establishment 
> are processed following the IEEE standard and could vary from platform 
> to platform but are not violent to the IEEE standard.
> 
> En-Wei, My recommendation is not to accept these patches. If you think 
> there is a HW/PHY problem - open a ticket on Intel PAE.
> 
> Sasha

I concur. I am wary of changing the behavior of some driver 
fundamentals, to satisfy a particular validation/certification flow, if 
there is no real functionality problem. It can open a big Pandora box.

Checking the Bugzilla report again, I am not sure we understand the 
issue fully:

[  143.141006] e1000e 0000:00:1f.6 enp0s31f6: NIC Link is Up 1000 Mbps 
Half Duplex, Flow Control: None
[  143.144878] e1000e 0000:00:1f.6 enp0s31f6: NIC Link is Down
[  146.838980] e1000e 0000:00:1f.6 enp0s31f6: NIC Link is Up 1000 Mbps 
Full Duplex, Flow Control: None

This looks like a very quick link "flap", following by proper link 
establishment ~3.7 seconds later. These ~3.7 seconds are in line of what 
link auto-negotiation would take (auto-negotiation is the default mode 
for this driver). The first print (1000 Mbps Half Duplex) actually makes 
no sense - it cannot be real link status since 1000/Half is not a 
supported speed. So it seems to me that actually the first "link up" is 
an incorrect/incomplete/premature reading, not the "link down".

--Dima