netdev - Re: [PATCH net-next 0/3] net: stmmac: add physical port identification support

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Message-ID: <707fbd5a-5e1b-4034-a1ca-337ec7eca1bd@lunn.ch>
Date: Thu, 4 Dec 2025 22:07:34 +0100
From: Andrew Lunn <andrew@...n.ch>
To: John Madieu <john.madieu.xa@...renesas.com>
Cc: prabhakar.mahadev-lad.rj@...renesas.com, andrew+netdev@...n.ch,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, geert+renesas@...der.be,
	biju.das.jz@...renesas.com, claudiu.beznea@...on.dev,
	linux@...linux.org.uk, magnus.damm@...il.com,
	mcoquelin.stm32@...il.com, alexandre.torgue@...s.st.com,
	netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH net-next 0/3]  net: stmmac: add physical port
 identification support

On Thu, Dec 04, 2025 at 04:37:26PM +0000, John Madieu wrote:
> This series adds physical port identification support to the stmmac driver,
> enabling userspace to query hardware-stable identifiers for network interfaces
> via ndo_get_phys_port_id() and ndo_get_phys_port_name().
> 
> On systems with multiple ethernet controllers sharing the same driver,
> physical port identification provides stable identifiers that persist
> across reboots and are independent of interface enumeration order.
> This is particularly useful for predictable network interface naming
> and for correlating interfaces with physical connectors.
> 
> The implementation follows a two-tier approach:
> 
> 1. Generic stmmac support: Default implementations use the permanent MAC
>    address as port ID and bus_id for port naming. This provides immediate
>    benefit for all stmmac-based platforms.

This information is already available to user space via
sysfs. udev/systemd can use this. How does systemd currently name
these interfaces using its rules?

https://www.freedesktop.org/software/systemd/man/latest/systemd.net-naming-scheme.html

> 2. Glue driver override: Platform drivers can provide custom callbacks
>    for hardware-specific identification schemes. The Renesas GBETH driver
>    implements this to support device tree-based port identification,
>    addressing cases where hardware lacks unique identification registers.

Why is the MAC address not sufficient? What makes Renesas GBETH
special so it needs something different?

	Andrew