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

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Date:   Thu, 10 Feb 2022 22:18:39 +0530
From:   Raag Jadav <raagjadav@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
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 08:12:59PM +0100, Andrew Lunn wrote:
> 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?
> 

Not sure if such behaviour is explicitly mentioned in the datasheet.
Maybe someone from Microchip can shed some light on this.

Cheers,
Raag

>      Andrew