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

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Message-ID: <b288926e-f9d6-48d5-9851-078a6c9912bf@intel.com>
Date: Fri, 10 May 2024 12:55:54 +0300
From: Sasha Neftin <sasha.neftin@...el.com>
To: Andrew Lunn <andrew@...n.ch>, "Ruinskiy, Dima" <dima.ruinskiy@...el.com>
CC: Ricky Wu <en-wei.wu@...onical.com>, <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 09/05/2024 16:46, Andrew Lunn wrote:
> On Thu, May 09, 2024 at 12:13:27PM +0300, Ruinskiy, Dima wrote:
>> 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).
> 
> That actually seems slow. It is normally a little over 1 second. I
> forget the exact number. But is the PHY being polled once a second,
> rather than being interrupt driven?
> 
>> 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.
> 
> It would be interesting to see what the link partner sees. What does
> it think the I219-LM is advertising? Is it advertising 1000BaseT_Half?

i219 parts come with LSI PHY. 1000BASE-T half-duplex is not supported. 
1000BASET half-duplex not advertised in IEEE 1000BASE-T Control Register 9.

> But why would auto-neg resolve to that if 1000BaseT_Full is available?
> 
>> So it seems to me that actually the first "link up" is an
>> incorrect/incomplete/premature reading, not the "link down".
> 
> Agreed. Root cause this, which looks like a real problem, rather than
> apply a band-aid for a test system.
> 
>        Andrew