netdev - Re: [PATCH net] net: mvpp2: Enable autoneg bypass for 1000BaseX/2500BaseX ports

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Date:   Fri, 29 May 2020 13:05:39 +0200
From:   Thomas Bogendoerfer <tbogendoerfer@...e.de>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: mvpp2: Enable autoneg bypass for
 1000BaseX/2500BaseX ports

On Thu, 28 May 2020 23:04:20 +0100
Russell King - ARM Linux admin <linux@...linux.org.uk> wrote:

> Can you explain this please?  Just as we think we understand what's
> going on here, you throw in a new comment that makes us confused.

sorry about that.

> You said previously that the mvpp2 was connected to a switch, which
> makes us think that you've got some DSA-like setup going on here.
> Does your switch drop its serdes link when all the external links
> (presumably the 10G SFP+ cages) fail?
> 
> Both Andrew and myself wish to have a complete picture before we
> move forward with this.

full understandable, I'll try by a small picture, which just
covers one switch:

        external ports
      |  |          |  |
*-----------------------------*
|     1  1          2  2      |
|                             |
|           switch            |
|                             |
|   1   2            1   2    |
*-----------------------------*
    |   |            |   |
    |   |            |   |
*----------*     *----------*
|   1   2  |     |   1   2  |
|          |     |          |
|  node 1  | ... |  node 8  |
|          |     |          |
*----------*     *----------*

External ports a grouped in ports to network 1 and network 2. If one of the
external ports has an established link, this link state will be propagated
to the internal ports. Same when both external ports of a network are down.

I have no control over the software running on the switch, therefore I can't
enable autoneg on the internal links. The internal nodes are running our
enterprise distribution and everything is working with SLE15SP1. With 
SLE15SP2 we've moved to kernel 5.3 and are now facing the problem, that links
on der internal nodes aren't coming up anymore.

I hope this makes things a little bit clearer.

Thomas.

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