netdev - Re: [PATCH] net: phy: marvell: avoid pause mode on SGMII-to-Copper for 88e151x

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Message-ID: <20171213164435.GA28466@lunn.ch>
Date:   Wed, 13 Dec 2017 17:44:35 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Russell King <rmk+kernel@...linux.org.uk>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Jon Nettleton <jon@...id-run.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: phy: marvell: avoid pause mode on SGMII-to-Copper
 for 88e151x

On Wed, Dec 13, 2017 at 09:22:09AM +0000, Russell King wrote:
> Observed on the 88e1512 in SGMII-to-Copper mode, negotiating pause
> is unreliable.  While the pause bits can be set in the advertisment
> register, they clear shortly after negotiation with a link partner
> commences irrespective of the cause of the negotiation.
> 
> While these bits may be correctly conveyed to the link partner on the
> first negotiation, a subsequent negotiation (eg, due to negotiation
> restart by the link partner, or reconnection of the cable) will result
> in the link partner seeing these bits as zero, while the kernel
> believes that it has advertised pause modes.
> 
> This leads to the local kernel evaluating (eg) symmetric pause mode,
> while the remote end evaluates that we have no pause mode capability.
> 
> Since we can't guarantee the advertisment, disable pause mode support
> with this PHY when used in SGMII-to-Copper mode.
> 
> The 88e1510 in RGMII-to-Copper mode appears to behave correctly.
> 
> Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew