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