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Date: Mon, 23 Feb 2026 15:04:01 -0800
From: Jakub Kicinski <kuba@kernel.org>
To: =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>
Cc: Andrew Lunn <andrew@lunn.ch>, netdev@vger.kernel.org, Donald Hunter
 <donald.hunter@gmail.com>, "David S. Miller" <davem@davemloft.net>, Eric
 Dumazet <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>, Simon
 Horman <horms@kernel.org>, Saeed Mahameed <saeedm@nvidia.com>, Tariq Toukan
 <tariqt@nvidia.com>, Leon Romanovsky <leon@kernel.org>, Andrew Lunn
 <andrew+netdev@lunn.ch>, Maxime Chevallier <maxime.chevallier@bootlin.com>,
 Michael Chan <michael.chan@broadcom.com>, Hariprasad Kelam
 <hkelam@marvell.com>, Ido Schimmel <idosch@nvidia.com>, Danielle Ratson
 <danieller@nvidia.com>, linux-kernel@vger.kernel.org,
 linux-rdma@vger.kernel.org
Subject: Re: [RFC net-next 0/4] ethtool: CMIS module diagnostic loopback
 support
Message-ID: <20260223150401.7993b11a@kernel.org>
In-Reply-To: <CAJ+HfNgXqpqDYsmAa-mpHnO82aDgC7XbyVw3TmXk-ySFmGA-JQ@mail.gmail.com>
References: <20260219130050.2390226-1-bjorn@kernel.org>
	<415c4922-cc8d-4e35-bbac-3a532f44d238@lunn.ch>
	<20260219160519.323041bf@kernel.org>
	<3b0949fa-0b05-4bce-86c0-2a7a058865a5@lunn.ch>
	<20260220131254.03874c4c@kernel.org>
	<CAJ+HfNgXqpqDYsmAa-mpHnO82aDgC7XbyVw3TmXk-ySFmGA-JQ@mail.gmail.com>
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On Sun, 22 Feb 2026 20:58:30 +0100 Bj=C3=B6rn T=C3=B6pel wrote:
> /* Loopback layers/scope
> enum ethtool_loopback_layer {
>     ETHTOOL_LB_LAYER_SW =3D 0,    /* Software/Kernel stack loopback */

What would that be? :)

>     ETHTOOL_LB_LAYER_MAC,        /* MAC/Controller internal */
>     ETHTOOL_LB_LAYER_PCS,        /* Physical Coding Sublayer (Digital) */
>     ETHTOOL_LB_LAYER_PMA,        /* SerDes / Analog-Digital boundary */
>     ETHTOOL_LB_LAYER_PMD,        /* Transceiver / Module internal */

In my mind the "layer" was supposed to tell core which driver to send
the request to. Same concept is used in the timestamp source selection.
PCS/PMA/PMD is both too fine grained when you have multiple PHYs in the
path, and does not cover all the possible loopback points.

>     ETHTOOL_LB_LAYER_EXT,        /* External physical plug/cable */

is EXT used somewhere to mean SFP already?