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

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Date:   Tue, 8 Feb 2022 20:12:59 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Raag Jadav <raagjadav@...il.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "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?

Or find out what this PHY does when the host is not performing auto
neg. Does the datasheet say anything about that?

     Andrew