Re: [PATCH net-next 1/3] dt-bindings: net: add nvmem-mac-address-offset property

[Michael Walle]

[adding Srinivas Kandagatla and Ansuel Smith]

Am 2021-04-16 00:27, schrieb Michael Walle:
> Am 2021-04-15 23:59, schrieb Rob Herring:
> > On Wed, Apr 14, 2021 at 05:43:49PM +0200, Andrew Lunn wrote:
> > > On Wed, Apr 14, 2021 at 05:26:55PM +0200, Michael Walle wrote:
> > > > It is already possible to read the MAC address via a NVMEM provider. But
> > > > there are boards, esp. with many ports, which only have a base MAC
> > > > address stored. Thus we need to have a way to provide an offset per
> > > > network device.
> > >
> > > We need to see what Rob thinks of this. There was recently a patchset
> > > to support swapping the byte order of the MAC address in a NVMEM. Rob
> > > said the NVMEM provider should have the property, not the MAC driver.
> > > This does seems more ethernet specific, so maybe it should be an
> > > Ethernet property?
> >
> > There was also this one[1]. I'm not totally opposed, but don't want to
> > see a never ending addition of properties to try to describe any
> > possible transformation.
>
> Agreed, that stuff like ASCII MAC address parsing should be done
> elsewhere. But IMHO adding an offset is a pretty common one (as also
> pointed out in [1]). And it also need to be a per ethernet device
> property.

I'm a bit up in the air on this, as I don't know how to proceed here.

To cite Rob from IRC:
  Not really up to me. All the people that care need to come up with
  something flexible enough for common/simple cases and that's not
  going to get extended with every new variation. What I don't want is
  a one-off that's then extended with another one-off.

I already pointed out that this property is per consumer as opposed
to something like endianess swap or parsing a given format. The latter
operates on the nvmem cell.

One random idea is to have a nvmem-cells-transformation (in the lack of
a better name) property for consumers, where you can have some kind of
simple operations like add:
  nvmem-cells-transformation = <NVMEM_ADD 1>
But is that something we really want to have? I'm not sure.

btw. given that there might be other means where a base mac address can
come from in the future, it might make sense to drop the "nvmem-"
prefix and just use "mac-address-offset" (or 
"base-mac-address-offset"?).

> [1] 
> https://patchwork.ozlabs.org/project/devicetree-bindings/patch/20200920095724.8251-4-ansuelsmth@xxxxxxxxx/

-michael