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Date:   Tue, 12 Sep 2023 18:15:52 +0200
From:   Andrew Lunn <andrew@lunn.ch>
To:     Maxime Chevallier <maxime.chevallier@bootlin.com>
Cc:     davem@davemloft.net, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        Vladimir Oltean <vladimir.oltean@nxp.com>,
        Oleksij Rempel <linux@rempel-privat.de>,
        =?iso-8859-1?Q?Nicol=F2?= Veronese <nicveronese@gmail.com>,
        thomas.petazzoni@bootlin.com,
        Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: Re: [RFC PATCH net-next 1/7] net: phy: introduce phy numbering and
 phy namespaces
Message-ID: <63bd3a9c-dacd-47e3-a34c-6e2e6a304d6c@lunn.ch>
References: <20230907092407.647139-1-maxime.chevallier@bootlin.com>
 <20230907092407.647139-2-maxime.chevallier@bootlin.com>
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On Thu, Sep 07, 2023 at 11:23:59AM +0200, Maxime Chevallier wrote:
> Link topologies containing multiple network PHYs attached to the same
> net_device can be found when using a PHY as a media converter for use
> with an SFP connector, on which an SFP transceiver containing a PHY can
> be used.
> 
> With the current model, the transceiver's PHY can't be used for
> operations such as cable testing, timestamping, macsec offload, etc.
> 
> The reason being that most of the logic for these configuration, coming
> from either ethtool netlink or ioctls tend to use netdev->phydev, which
> in multi-phy systems will reference the PHY closest to the MAC.
> 
> Introduce a numbering scheme allowing to enumerate PHY devices that
> belong to any netdev, which can in turn allow userspace to take more
> precise decisions with regard to each PHY's configuration.

I think we need more than a number. Topology needs to be a core
concept here, otherwise how is the user supposed to know which PHY to
use cable test on, etc.

However, it is not a simple problem. An SFP PHY should be the last in
a chain. So you can infer something from that. When we start adding
MII muxes, they will need to be part of the modal.

    Andrew