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

[Tim Harvey]

On Tue, Aug 9, 2022 at 2:31 PM Pali Rohár <pali at kernel.org> wrote:
>
> On Tuesday 09 August 2022 16:48:23 Sean Anderson wrote:
> > On 8/8/22 5:45 PM, Michal Suchánek wrote:
> > > On Mon, Aug 08, 2022 at 02:38:35PM -0700, Stephen Hemminger wrote:
> > >> On Mon, 8 Aug 2022 23:09:45 +0200
> > >> Michal Suchánek <msuchanek at suse.de> wrote:
> > >>
> > >> > On Mon, Aug 08, 2022 at 03:57:55PM -0400, Sean Anderson wrote:
> > >> > > Hi Tim,
> > >> > >
> > >> > > On 8/8/22 3:18 PM, Tim Harvey wrote:
> > >> > > > Greetings,
> > >> > > >
> > >> > > > I'm trying to understand if there is any implication of 'ethernet<n>'
> > >> > > > aliases in Linux such as:
> > >> > > >         aliases {
> > >> > > >                 ethernet0 = &eqos;
> > >> > > >                 ethernet1 = &fec;
> > >> > > >                 ethernet2 = &lan1;
> > >> > > >                 ethernet3 = &lan2;
> > >> > > >                 ethernet4 = &lan3;
> > >> > > >                 ethernet5 = &lan4;
> > >> > > >                 ethernet6 = &lan5;
> > >> > > >         };
> > >> > > >
> > >> > > > I know U-Boot boards that use device-tree will use these aliases to
> > >> > > > name the devices in U-Boot such that the device with alias 'ethernet0'
> > >> > > > becomes eth0 and alias 'ethernet1' becomes eth1 but for Linux it
> > >> > > > appears that the naming of network devices that are embedded (ie SoC)
> > >> > > > vs enumerated (ie pci/usb) are always based on device registration
> > >> > > > order which for static drivers depends on Makefile linking order and
> > >> > > > has nothing to do with device-tree.
> > >> > > >
> > >> > > > Is there currently any way to control network device naming in Linux
> > >> > > > other than udev?
> > >> > >
> > >> > > You can also use systemd-networkd et al. (but that is the same kind of mechanism)
> > >> > >
> > >> > > > Does Linux use the ethernet<n> aliases for anything at all?
> > >> > >
> > >> > > No :l
> > >> >
> > >> > Maybe it's a great opportunity for porting biosdevname to DT based
> > >> > platforms ;-)
> > >>
> > >> Sorry, biosdevname was wrong way to do things.
> > >> Did you look at the internals, it was dumpster diving as root into BIOS.
> > >
> > > When it's BIOS what defines the names then you have to read them from
> > > the BIOS. Recently it was updated to use some sysfs file or whatver.
> > > It's not like you would use any of that code with DT, anyway.
> > >
> > >> Systemd-networkd does things in much more supportable manner using existing
> > >> sysfs API's.
> > >
> > > Which is a dumpster of systemd code, no thanks.
> > >
> > > I want my device naming independent of the init system, especially if
> > > it's systemd.
> >
> > Well, there's always nameif...
> >
> > That said, I have made [1] for people using systemd-networkd.
> >
> > --Sean
> >
> > [1] https://github.com/systemd/systemd/pull/24265
>
> Hello!
>
> In some cases "label" DT property can be used also as interface name.
> For example this property is already used by DSA kernel driver.
>
> I created very simple script which renames all interfaces in system to
> their "label" DT property (if there is any defined).
>
> #!/bin/sh
> for iface in `ls /sys/class/net/`; do
>         for of_node in of_node device/of_node; do
>                 if test -e /sys/class/net/$iface/$of_node/; then
>                         label=`cat /sys/class/net/$iface/$of_node/label 2>/dev/null`
>                         if test -n "$label" && test "$label" != "$iface"; then
>                                 echo "Renaming net interface $iface to $label..."
>                                 up=$((`cat /sys/class/net/$iface/flags 2>/dev/null || echo 1` & 0x1))
>                                 if test "$up" != "0"; then
>                                         ip link set dev $iface down
>                                 fi
>                                 ip link set dev $iface name "$label" && iface=$label
>                                 if test "$up" != "0"; then
>                                         ip link set dev $iface up
>                                 fi
>                         fi
>                         break
>                 fi
>         done
> done
>
> Maybe it would be better first to use "label" and then use ethernet alias?

I've been wondering the same as well which made me wonder what the
history of the 'aliases' node is and why its not used in most cases in
Linux. I know for the SOC's I work with we've always defined aliases
for ethernet<n>, gpio<n>, serial<n>, spi<n>, i2c<n>, mmc<n> etc. Where
did this practice come from and why are we putting that in Linux dts
files it if it's not used by Linux?

Best Regards,

Tim