netdev - Re: [PATCH] net: phy: mscc: enable MAC SerDes autonegotiation

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Message-ID: <YgKT6W7y69AGiFd7@shell.armlinux.org.uk>
Date:   Tue, 8 Feb 2022 16:01:45 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Raag Jadav <raagjadav@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Steen Hegelund <steen.hegelund@...rochip.com>,
        Bjarni Jonasson <bjarni.jonasson@...rochip.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: mscc: enable MAC SerDes autonegotiation

On Tue, Feb 08, 2022 at 09:27:52PM +0530, Raag Jadav wrote:
> On Tue, Feb 08, 2022 at 03:09:48AM +0100, Andrew Lunn wrote:
> > > MAC implementation[1] in a lot of NXP SoCs comes with in-band aneg enabled
> > > by default, and it does expect Clause 37 auto-negotiation to complete
> > > between MAC and PHY before the actual data transfer happens.
> > > 
> > > [1] https://community.nxp.com/pwmxy87654/attachments/pwmxy87654/t-series/3241/1/AN3869(1).pdf
> > > 
> > > I faced such issue while integrating VSC85xx PHY
> > > with one of the recent NXP SoC having similar MAC implementation.
> > > Not sure if this is a problem on MAC side or PHY side,
> > > But having Clause 37 support should help in most cases I believe.
> > 
> > So please use this information in the commit message.
> > 
> > The only danger with this change is, is the PHY O.K with auto-neg
> > turned on, with a MAC which does not actually perform auto-neg? It
> > could be we have boards which work now because PHY autoneg is turned
> > off.
> > 
> 
> Introducing an optional device tree property could be of any help?

Preferably not. We do need some way that the MAC and PHY can co-operate
to work out whether inband should be used or not. Vladimir had some
patches for that a while back which were touching phylib and phylink
which may be worth looking into to see whether some of that can be
applied to your situation.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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