netdev - Re: ethernet "bus" number in DTS ?

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Date:   Tue, 23 Oct 2018 18:02:52 +0000
From:   Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
To:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>
CC:     "andrew@...n.ch" <andrew@...n.ch>
Subject: Re: ethernet "bus" number in DTS ?

On Tue, 2018-10-23 at 10:03 -0700, Florian Fainelli wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
> 
> 
> On 10/23/18 9:49 AM, Joakim Tjernlund wrote:
> > SPI (and others) has a way to define bus number in a aliases:
> >       aliases {
> >               ethernet4 = &enet4;
> >               ethernet0 = &enet0;
> >               ethernet1 = &enet1;
> >               ethernet2 = &enet2;
> >               ethernet3 = &enet3;
> >               spi0 = &spi0
> >       };
> > The 0 in the spi0 alias will translate to bus num 0 so one can control the /dev nodes, like /dev/spidev0
> > I am looking for the same for ethernet devices:
> >  ethernet4 = &enet4;  /* should become eth4 */
> >  ethernet0 = &enet0;  /* should become eth0 */
> > but I cannot find something like that for eth devices.
> > 
> > Could such functionality be added?
> 
> It could, do we want and need to, no. You have the Ethernet alias in
> /sys/class/net/*/device/uevent already that would allow you to perform
> that (re)naming in user-space:
> 
> # cat /sys/class/net/eth0/device/uevent
> DRIVER=bcmgenet
> OF_NAME=ethernet
> OF_FULLNAME=/rdb/ethernet@...80000
> OF_TYPE=network
> OF_COMPATIBLE_0=brcm,genet-v5
> OF_COMPATIBLE_N=1
> OF_ALIAS_0=eth0                 <==================
> MODALIAS=of:NethernetTnetworkCbrcm,genet-v5

Yes, one can if one uses udev and can find something to identify the hw I/F with, my
cat /sys/class/net/eth0/device/uevent looks like:
DRIVER=fsl_dpa
MODALIAS=platform:dpaa-ethernet

not sure mdev supports this, does it?
Our simple installer FS(initramfs) doesn't have either udev or mdev.

I also noted that using status = "disabled" didn't work either to create a fix name scheme.
Even worse, all the eth I/F after gets renumbered. It seems to me there
is value in having stability in eth I/F naming at boot.
Then userspace(udev) can rename if need be. 

Sure would like to known more about why this feature is not wanted ?

I found
  https://patchwork.kernel.org/patch/4122441/
You quote policy as reason but surely it must be better to
have something stable, connected to the hardware name, than semirandom naming?

 Jocke