linux-kernel - Re: [PATCH net-next v2 2/3] net: ethtool: Add impedance mismatch result code to cable test

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Date: Fri, 29 Mar 2024 08:10:58 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Paweł Dembicki <paweldembicki@...il.com>
Cc: netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>, Heiner Kallweit
 <hkallweit1@...il.com>, Russell King <linux@...linux.org.uk>, "David S.
 Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo
 Abeni <pabeni@...hat.com>, Stefan Eichenberger <eichest@...il.com>, Dimitri
 Fedrau <dima.fedrau@...il.com>, Kory Maincent <kory.maincent@...tlin.com>,
 Maxime Chevallier <maxime.chevallier@...tlin.com>, Shay Agroskin
 <shayagr@...zon.com>, Ahmed Zaki <ahmed.zaki@...el.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 2/3] net: ethtool: Add impedance mismatch
 result code to cable test

On Fri, 29 Mar 2024 10:31:10 +0100 Paweł Dembicki wrote:
> > I'm not a cable expert but going purely by the language
> > abnormal != mismatch. Mismatch indicates there are two
> > values we are comparing.  
> 
> Impedance mismatch can be detected because some parts of the cable may
> have different (abnormal) impedance, causing reflections at those
> points. Ethernet cables should have a characteristic impedance of 100
> Ohms, so any mismatch from this value is considered abnormal.

I see, makes sense.

> I can provide a rephrased version if the commit description was not
> detailed enough.

That'd be great. Or maybe even better a short comment above the enum
entry?