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

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Date: Thu, 9 May 2024 15:46:42 +0200
From: Andrew Lunn <andrew@...n.ch>
To: "Ruinskiy, Dima" <dima.ruinskiy@...el.com>
Cc: Sasha Neftin <sasha.neftin@...el.com>,
	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 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?
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