Date:   Thu, 23 Mar 2017 11:30:04 +0000
From:   Maxime Morin <maxime.morin@...ec.com>
To:     Stas Sergeev <stsp@...t.ru>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "thomas.petazzoni@...e-electrons.com" 
        <thomas.petazzoni@...e-electrons.com>
Subject: Re: Problem: net: mvneta: auto-negotiation with disconnected network
 cable

Hi,
Thank you very much for your help and your reactivity! See my answer bellow:

> 22.03.2017 16:23, Maxime Morin пишет:
> > Hi all,
> >
> > I work on an embedded platform based on the Marvell Armada 88F6707, that is connected to a Marvell Alaska 88E1512 ethernet transceiver. A defect has appeared recently, and it turns out to be a regression on the network part. There is a complete lost of the network when following these steps:
> >      1) boot the board with the network cable disconnected
> >      2) run the following commands (or equivalent):
> >          ip link set eth0 up
> >          ip addr add 10.0.0.80/24 dev eth0
> >          ethtool -s eth0 autoneg on #this is the command that really breaks the network
> Why do you call it a regression, if previously
> this command did nothing at all?

I called that a regression because we still pass through the function phy_ethtool_sset(), which I though was also doing something about the auto-negotiation. But apparently not.

> 
> >      3) plug the network cable
> >          => there is no network, and no way to have it back except by rebooting
> > If I do not launch the "ethtool" command, when I plug the network cable it works, so it really seems to be related to the auto-negotiation set to "on" when the network cable has never been > connected.
> So if you do that with the cable plugged it, there
> is no breakage?
> When you do "ethtool -s eth0 autoneg off" it doesn't
> revive?

Unfortunately no, it does not. I tried many things with ethtool, but it never gets back.

> > I did a "git bisect" to find when the regression was introduced, because it previously worked with kernel 4.4, but not with the recent ones. The commit that made appear the issue is this one: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0c0744fc1dd5b
> > If I remove on mvneta.c the part that was added on this commit on the function mvneta_ethtool_set_link_ksettings (mvneta_ethtool_set_settings at that time), I do not have the issue, but I can't call that a fix...
> > So, could it be a driver issue, or maybe a wrong configuration somewhere? If you need additional information to reproduce the problem please ask me, I will be as responsive as possible.
> It seems mvneta_set_autoneg() does some non-symmetric
> things. It clears
> MVNETA_GMAC_FORCE_LINK_PASS |
> MVNETA_GMAC_FORCE_LINK_DOWN |
> MVNETA_GMAC_AN_FLOW_CTRL_EN
> when enabling autoneg, and does not restore these flags
> when disabling it. Try to make it to set or to restore these
> flags and see if that makes "ethtool -s eth0 autoneg off" to
> get the network back alive> .

As you suggested, I just set these three flags when the function is called with "enable" set to 0. And it works!
Actually, I did not even have to set autoneg to off. When the module is probed, the default param are applied (mvneta_defaults_set()), and mvneta_set_autoneg() is called with "enable" to 0, and it seems to fix everything. I tested it then, by setting autoneg to off/on, booting with or without the cable plugged, and I failed to break it. It seems to be fixed. Should I submit a patch? (would be the first time...)

Again, thanks a lot for your help.

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