netdev - Re: ethernet<n> dt aliases implications in U-Boot and Linux

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Date:   Wed, 10 Aug 2022 17:35:10 +0200
From:   Michal Suchánek <msuchanek@...e.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Tim Harvey <tharvey@...eworks.com>,
        Pali Rohár <pali@...nel.org>,
        Sean Anderson <sean.anderson@...o.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        netdev <netdev@...r.kernel.org>, u-boot <u-boot@...ts.denx.de>,
        Device Tree Mailing List <devicetree@...r.kernel.org>
Subject: Re: ethernet<n> dt aliases implications in U-Boot and Linux

On Wed, Aug 10, 2022 at 05:17:56PM +0200, Andrew Lunn wrote:
> > > I guess you are new to the netdev list :-)
> > > 
> > > This is one of those FAQ sort of things, discussed every
> > > year. Anything like this is always NACKed. I don't see why this time
> > > should be any different.
> > > 
> > > DSA is somewhat special because it is very old. It comes from before
> > > the times of DT. Its DT binding was proposed relatively earl in DT
> > > times, and would be rejected in modern days. But the rules of ABI mean
> > > the label property will be valid forever. But i very much doubt it
> > > will spread to interfaces in general.
> > 
> > And if this is a FAQ maybe you can point to a summary (perhaps in
> > previous mail discusssion) that explains how to provide stable interface
> > names for Ethernet devices on a DT based platform?
> 
> As far so the kernel is concerned, interface names are unstable. They
> have never been truly stable, but they have got more unstable in the
> past decade with multiple busses being probed in parallel, which did
> not happen before so much.
> 
> > On x86 there is a name derived from the device location in the bus
> > topology
> 
> This is nothing to do with x86. That is userspace, e.g. systemd,
> renaming the interfaces. This applies for any architecture for which
> systemd runs on.
> 
> > which may be somewhat stable but it is not clear that it
> > cannot change, and there is an optional BIOS provided table that can
> > asssign meaningful names to the interfaces.
> 
> I doubt the kernel is looking at ACPI tables. It is user space which
> does that.
> 
> The kernel provides udev with a bunch of information about the
> interface, its bus location, MAC address, etc. Userspace can then
> decide what it wants to call it, and what its alternative names are,
> etc.
> 
> Also, this is not just a network interface name problem. Any device
> with a number/letter in it is unstable. I2C bus devices: i2c0,
> i2c1... SPI bus deviceS: spi0, spi1...,

Thees do have numbered aliases in the DT. I don't know if the kernel
uses them for anything.

> Block devices, sda, sdb, sdc,

These too, at least mmc.

Thanks

Michal