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

[Andrew Lunn]

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