netdev - Re: [PATCH net-next] net: phy: aquantia: add downshift support

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Message-ID: <20190321083827.GD2900@lunn.ch>
Date:   Thu, 21 Mar 2019 09:38:27 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: phy: aquantia: add downshift support

On Wed, Mar 20, 2019 at 10:15:10PM +0100, Heiner Kallweit wrote:
> Aquantia PHY's of the AQR107 family support the downshift feature.
> Add support for it as standard PHY tunable so that it can be controlled
> via ethtool.
> The AQCS109 supports a proprietary 2-pair 1Gbps mode. If two such PHY's
> are connected to each other with a 2-pair cable, they may not be able
> to establish a link if both advertise modes >= 1Gbps. Therefore enable
> downshift per default on this model.

Hi Heiner

Is there any way to know it has done a downshift?

Florian said the Intel drivers print a message when they downshift. It
could be interesting to know, especially when a PHY goes from 1G to
100M.

Even for a downshift to 1000Base-T2, i'm guessing for most use cases,
this means the cable is partially broken, and it serves as an early
warning it needs replacing.

	Andrew