netdev - Re: [PATCH net-next] net: phy: marvell: Ensure SGMII auto-negotiation is enabled for 88E1111

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Date:   Sat, 13 Feb 2021 01:28:14 +0000
From:   Robert Hancock <robert.hancock@...ian.com>
To:     "linux@...linux.org.uk" <linux@...linux.org.uk>
CC:     "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: phy: marvell: Ensure SGMII auto-negotiation
 is enabled for 88E1111

On Sat, 2021-02-13 at 01:09 +0000, Russell King - ARM Linux admin wrote:
> On Fri, Feb 12, 2021 at 06:26:29PM -0600, Robert Hancock wrote:
> > When 88E111 is operating in SGMII mode, auto-negotiation should be enabled
> 
> 88E1111.

yup..

> 
> > on the SGMII side so that the link will come up properly with PCSes which
> > normally have auto-negotiation enabled. This is normally the case when the
> > PHY defaults to SGMII mode at power-up, however if we switched it from some
> > other mode like 1000BaseX, as may happen in some SFP module situations,
> > it may not be.
> 
> Do you actually have a module where this applies?
> 
> I have modules that do come up in 1000base-X mode, but do switch to
> SGMII mode with AN just fine. So I'm wondering what the difference is.

I saw this with a Finisar FCLF8520P2BTL, which defaults to 1000Base-X with
host-side auto-negotiation disabled. So presumably the auto-negotiation
disabled state carries over when it is switched to SGMII mode. I previously
wrote a patch ("net: phy: marvell: add special handling of Finisar modules with
88E1111") which enabled auto-negotiation for 1000Base-X mode, but we are trying
to switch over to using SGMII with these now.

> 
-- 
Robert Hancock
Senior Hardware Designer, Calian Advanced Technologies
www.calian.com