netdev - Re: Problem: net: mvneta: auto-negotiation with disconnected network cable

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Date:   Fri, 24 Mar 2017 14:39:54 +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


>From: Stas Sergeev <stsp@...t.ru>
>
>23.03.2017 14:30, Maxime Morin пишет:
>> 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.
>It does, but with mdio.
>But in the MAC driver we have another autoneg
>now, which is a great confusion. mvneta_set_autoneg()
>could have been named mvneta_set_inband_autoneg(),
>which would already help a lot. If you prepare the patch-set,
>you can include such renaming
>
>>>> 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!
>Am I right that it works only when you set autoneg
>to "off", while "on" still does not give you any link detect?
>So this is a partial fix, right?
No. It actually works for both modes in this case.

>> 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.
>It turns off SGMII-specific autoned and starts using
>mdio autoneg instead... a great confusion.
>
>> 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...)
>After looking up my other patches to this driver, I
>can see that
>
>MVNETA_GMAC_FORCE_LINK_PASS |
>MVNETA_GMAC_FORCE_LINK_DOWN
>
>are left cleared willingly. I suspect that MVNETA_GMAC_AN_FLOW_CTRL_EN
>breaks things for you. Could you please try with setting
>back only this flag?
I tested it, but not only this case. There are three flags, so 8 possibilities (and already 2 tested), so I tested all of them one by one.
And it shows that:
- when MVNETA_GMAC_FORCE_LINK_PASS is not set,
no matter the values of MVNETA_GMAC_FORCE_LINK_{PASS,DOWN}, the issue is reproduced
- when MVNETA_GMAC_FORCE_LINK_PASS is set,
no matter the values of MVNETA_GMAC_FORCE_LINK_{PASS,DOWN}, the network works (autoneg set off/on, booting with cable plugged/unplugged, etc)