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From: Timur Tabi <timur@qti.qualcomm.com>
Subject: Re: [PATCH 2/2] at803x: double check SGMII side autoneg
Date: Wed, 24 May 2017 16:32:48 -0500
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Cc: Matthias May <matthias.may@neratec.com>,
        Zefir Kurtisi <zefir.kurtisi@neratec.com>,
        <netdev@vger.kernel.org>, David Miller <davem@davemloft.net>,
        Manoj Iyer <manoj.iyer@canonical.com>, <jhugo@codeaurora.org>
To: Florian Fainelli <f.fainelli@gmail.com>,
        Timur Tabi <timur@qti.qualcomm.com>,
        Andrew Lunn <andrew@lunn.ch>
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On 05/24/2017 04:28 PM, Florian Fainelli wrote:

> Yes phydev->lock which is used to serialize the state machine state changes.
>
> Most PHYs have many more registers than the 15 standard exposed
> directly, and so you need indirect reads/writes to access these
> registers, which typically involve switching a particular page, doing
> the indirect register access, and then flipping the page back. If you
> interrupt that scheme one way or another, your reads and writes are all
> messed up.

Ah, and the at803x is a device like that.

At worst, the autopoll feature could read a register from the wrong 
page, and think that the link state has changed when it hasn't.  But 
that's still bad, and all my problems do revolve around link states.

>> I forgot one detail.  Every time you do an MDIO read/write, it
>> temporarily disables the feature.  Although, I think that's not relevant
>> to your point.
>
> Is that done by the HW itself, or is this under SW control exclusively.

Software.