netdev - Re: [RFC PATCH net-next 1/7] net: phy: introduce phy numbering and phy namespaces

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Date: Tue, 12 Sep 2023 18:15:52 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Oleksij Rempel <linux@...pel-privat.de>,
	Nicolò Veronese <nicveronese@...il.com>,
	thomas.petazzoni@...tlin.com,
	Christophe Leroy <christophe.leroy@...roup.eu>
Subject: Re: [RFC PATCH net-next 1/7] net: phy: introduce phy numbering and
 phy namespaces

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