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

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Date:   Thu, 21 Mar 2019 19:49:49 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
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 21.03.2019 09:38, Andrew Lunn wrote:
> 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.
> 
Good point, after a brief look at the datasheet this should be possible.

> 	Andrew
> .
> 
Heiner