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 10:31:10 +0100
From: Paweł Dembicki <paweldembicki@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
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

pt., 29 mar 2024 o 03:02 Jakub Kicinski <kuba@...nel.org> napisał(a):
>
> On Wed, 27 Mar 2024 17:29:13 +0100 Pawel Dembicki wrote:
> > This commit introduces a new result code:
> > ETHTOOL_A_CABLE_RESULT_CODE_IMPEDANCE_MISMATCH
> > which represents the results of a cable test indicating abnormal impedance.
>
> 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 can
provide a rephrased version if the commit description was not detailed
enough.