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

From: Andrew Lunn <[email-masked]>
Date: Thu, 21 Mar 2019 09:38:27 +0100

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