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 <20240327162918.2426792-2-paweldembicki@gmail.com> <20240328190226.7aab8b76@kernel.org>
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From: =?UTF-8?Q?Pawe=C5=82_Dembicki?= <paweldembicki@gmail.com>
Date: Fri, 29 Mar 2024 10:31:10 +0100
Message-ID: <CAJN1KkxcX9dfhMVvQCFLosTgO5U2tAjvHEO-prViSacOB6DQRg@mail.gmail.com>
Subject: Re: [PATCH net-next v2 2/3] net: ethtool: Add impedance mismatch
 result code to cable test
To: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org, Andrew Lunn <andrew@lunn.ch>, 
	Heiner Kallweit <hkallweit1@gmail.com>, Russell King <linux@armlinux.org.uk>, 
	"David S. Miller" <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, 
	Paolo Abeni <pabeni@redhat.com>, Stefan Eichenberger <eichest@gmail.com>, 
	Dimitri Fedrau <dima.fedrau@gmail.com>, Kory Maincent <kory.maincent@bootlin.com>, 
	Maxime Chevallier <maxime.chevallier@bootlin.com>, Shay Agroskin <shayagr@amazon.com>, 
	Ahmed Zaki <ahmed.zaki@intel.com>, linux-kernel@vger.kernel.org
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pt., 29 mar 2024 o 03:02 Jakub Kicinski <kuba@kernel.org> napisa=C5=82(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 impeda=
nce.
>
> I'm not a cable expert but going purely by the language
> abnormal !=3D 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.