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Date:   Wed, 27 Feb 2019 13:42:56 -0800
From:   Stephen Hemminger <stephen@networkplumber.org>
To:     Florian Fainelli <f.fainelli@gmail.com>
Cc:     Harini Katakam <harinik@xilinx.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Nicolas Ferre <nicolas.ferre@atmel.com>,
        David Miller <davem@davemloft.net>,
        Michal Simek <michal.simek@xilinx.com>,
        Harini Katakam <harini.katakam@xilinx.com>,
        Harini Katakam <harinikatakamlinux@gmail.com>
Subject: Re: Request for suggestion on net device re-naming/re-ordering
 based on DT alias
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On Wed, 27 Feb 2019 10:45:44 -0800
Florian Fainelli <f.fainelli@gmail.com> wrote:

> On 2/27/19 10:40 AM, Stephen Hemminger wrote:
> > On Wed, 27 Feb 2019 17:24:03 +0530
> > Harini Katakam <harinik@xilinx.com> wrote:
> >  =20
> >> Hi,
> >>
> >> We've had some users requesting control over net device name order
> >> when multiple ethernet devices are present on a system. I've tried a
> >> few solutions to this and looked it up on forums. But I apologize if
> >> I have missed something.
> >>
> >> I know that the current system allocates eth<n> as per probe order
> >> but that is obviously not stably controlled by user (tried DT
> >> re-ordering and defer probe). One solution is to use DT alias names
> >> to write to (net_device)->name as follows:
> >> Devicetree:
> >> aliases {
> >>    ethernet0 =3D &mac1;
> >>    ethernet1 =3D &mac0;
> >> };
> >> Driver probe:
> >> +       /* Read ethernet DT alias id and assign to right device name*/
> >> +       id =3D of_alias_get_id(np, "ethernet");
> >> +       if (id < 0) {
> >> +               dev_warn(&pdev->dev, "failed to get alias id (%u)\n", =
id);
> >> +               return id;
> >> +       }
> >> +       snprintf(dev->name, sizeof(dev->name), "eth%d", id);
> >> +
> >>
> >> These three drivers seem to have something similar for mdio/phy bus ID=
s:
> >> drivers/net/ethernet/broadcom/genet/bcmmii.c:409: id =3D
> >> of_alias_get_id(dn, "eth");
> >> drivers/net/ethernet/samsung/sxgbe/sxgbe_platform.c:43: plat->bus_id =
=3D
> >> of_alias_get_id(np, "ethernet");
> >> drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c:404:
> >> plat->bus_id =3D of_alias_get_id(np, "ethernet");
> >>
> >> Drawback: This approach will break if alias is not provided for one
> >> of the interfaces on board. Not to mention, there could be systems
> >> with multiple ethernet makes (for ex. Cadence macb and Xilinx axienet)
> >> If one of the drivers does not have an alias read mechanism, it is
> >> possible to have clashing ID assignments. Is there any way this
> >> solution can be changed to be stable/acceptable?
> >>
> >> One other alternative I've tried is netdev kernel bootargs but this
> >> device name was not being picked by the kernel:
> >> https://www.kernel.org/doc/html/v4.19/admin-guide/kernel-parameters.ht=
ml
> >> netdev=3D <mac1=E2=80=99s interrupt id>, <mac1=E2=80=99s base address>=
, eth0
> >> netdev=3D<mac0=E2=80=99s interrupt id>, <mac0=E2=80=99s base address>,=
 eth1
> >>
> >> Could you please suggest any alternatives?
> >> Thanks!
> >>
> >> Regards,
> >> Harini =20
> >=20
> > Device naming is a hard problem, and there is no perfect solution.
> >=20
> > Device tree should be providing hints to userspace policy for naming, n=
ot
> > trying to do it in the kernel.  =20
>=20
> And Device Tree does already, if you look at the uevent attributes that
> the kernel sends, there should be ample information to uniquely
> determine which physical network device the network device maps to, e
> for instance:
>=20
> cat /sys/class/net/eth*/device/uevent
> DRIVER=3Dbrcm-systemport
> OF_NAME=3Dethernet
> OF_FULLNAME=3D/rdb/ethernet@9300000
> OF_TYPE=3Dnetwork
> OF_COMPATIBLE_0=3Dbrcm,systemportlite-v1.00
> OF_COMPATIBLE_1=3Dbrcm,systemport
> OF_COMPATIBLE_N=3D2
> OF_ALIAS_0=3Deth0
> MODALIAS=3Dof:NethernetTnetworkCbrcm,systemportlite-v1.00Cbrcm,systemport

Then you need to work with udev developers to handle device tree better.

By design ethN is not used for persistent naming, only other names like ens=
X.
This allows for safer renaming and provides way to handle devices that may
not match any rules.

Most of udev naming is based of properties in sysfs like pci-slot, port etc.
If you had that available on these devices, it would just work now.