ethernet "bus" number in DTS ?

[Florian Fainelli]

On 10/23/18 1:02 PM, Joakim Tjernlund wrote:
> On Tue, 2018-10-23 at 11:20 -0700, Florian Fainelli wrote:
>>
>> On 10/23/18 11:02 AM, Joakim Tjernlund wrote:
>>> On Tue, 2018-10-23 at 10:03 -0700, Florian Fainelli wrote:
>>>>
>>>>
>>>> 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 at f0480000
>>>> 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
>>
>> Does not dpaa have a notion of Ethernet ports and those should have
>> proper information? Maybe that is part of your problem here, it should
>> have the OF_ALIAS information somehow available.
> 
> I cannot say ATM, but this lack of standard does not make it easier to rename I/F's in udev.
> 
>>
>>> not sure mdev supports this, does it?
>>> Our simple installer FS(initramfs) doesn't have either udev or mdev.
>>
>> I don't know, but you could have a simple shell script that looks at
>> specific network device properties to decide on the naming and call
>> ifrename.
> 
> This reinventing of the wheel is what I am trying to avoid.

Embedded is all about being a special snowflake and re-inventing the
wheel, but having some desktop-like distribution user-space would
certainly allow you to re-invent other parts of the wheel.

> 
>>
>>> 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?
>>
>> If the Device Tree nodes are ordered by ascending base register address,
>> my understanding is that you get the same order as far as
>> platform_device creation goes, this may not be true in the future if Rob
>> decides to randomize that, but AFAICT this is still true. This may not
>> work well with status = disabled properties being inserted here and
>> there, but we have used that here and it has worked for as far as I can
>> remember doing it.
> 
> I recall it is the order in which the eth alias appear that controls the naming,
> not 100% sure though.

Aliases are not looked up at all by the platform bus code other that
with of_get_alias() and friends, it is the order in which the nodes are
declared in the Device Tree, preferably ordered by base address that
dictates the order in which platform devices are created.

> 
>>
>> Second, you might want to name network devices ethX, but what if I want
>> to name them ethernetX or fooX or barX? Should we be accepting a
>> mechanism in the kernel that would allow someone to name the interfaces
>> the way they want straight from a name being provided in Device Tree?
> 
> I just want to have stable boot names, aka ethX, which can defined in
> the platforms DT. Then userspace can go from there to whatever it needs,
> udev could possibly use these stable boot names to identify the I/F's to rename.
> 
> ATM, it is pretty hard to even use udev when /sys/class/net/eth0/device/uevent
> can look different even for OF created interfaces.

network devices have a gazillion of other sysfs attributes that all make
them unique enough to create stable names.

> 
>>
>> Aliases are fine for providing relative stability within the Device Tree
>> itself and boot programs that might need to modify the Device Tree (e.g:
>> inserting MAC addresses) such that you don't have to encode logic to
>> search for nodes by compatible strings etc. but outside of that use
>> case, it seems to me that you can resolve every naming decision in
>> user-space.
> 
> Well, you can resolve MAC address assignment in user space too but most
> will agree that is not convenient. I suggest it is also handy to have
> some control of I/F enumeration(ethX that is) from platform code like DT.

If that is what you desire because you do not want to use user-space to
do that job, that is probably fine, it's open source after all, an not
every patch is a candidate for being included upstream. A patch doing
what you describe would likely be rejected again.
-- 
Florian