netdev - Re: Link down reasons

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Message-ID: <20200527213843.GC818296@lunn.ch>
Date:   Wed, 27 May 2020 23:38:43 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Amit Cohen <amitc@...lanox.com>
Cc:     mlxsw <mlxsw@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "o.rempel@...gutronix.de" <o.rempel@...gutronix.de>
Subject: Re: Link down reasons

On Wed, May 27, 2020 at 03:41:22PM +0000, Amit Cohen wrote:
> Hi Andrew,
> 
> We are planning to send a set that exposes link-down reason in ethtool.
> 
> It seems that the ability of your set “Ethernet cable test support” can be
> integrated with link-down reason.
> 
>  
> 
> The idea is to expose reason and subreason (if there is):
> 
> $ ethtool ethX
> 
> …
> 
> Link detected: no (No cable) // No sub reason
> 
>  
> 
> $ ethtool ethY
> 
> Link detected: no (Autoneg failure, No partner detected)
> 
>  
> 
> Currently we have reason “cable issue” and subreasons “unsupported cable” and
> “shorted cable”.
> 
> The mechanism of cable test can be integrated and allow us report “cable issue”
> reason and “shorted cable” subreason.

Hi Amit

I don't really see them being combinable. First off, your API seems
too limiting. How do you say which pair is broken, or at what
distance? What about open cable, as opposed to shorted cable?

So i would suggest:

Link detected: no (cable issue)

And then recommend the user uses ethtool --cable-test to get all the
details, and you have a much more flexible API to provide as much or
as little information as you have.

   Andrew