Subject: Re: R: [PATCH v2 4/4] dt-bindings: net: Document use of mac-address-increment

From: Andrew Lunn <[email-masked]>
Date: Sun, 20 Sep 2020 03:22:16 +0200

On Sun, Sep 20, 2020 at 02:39:39AM +0200, [email-masked] wrote:
> 
> 
> > -----Messaggio originale-----
> > Da: Andrew Lunn <[email-masked]>
> > Inviato: domenica 20 settembre 2020 02:31
> > A: Ansuel Smith <[email-masked]>
> > Cc: Miquel Raynal <[email-masked]>; Richard Weinberger
> > <[email-masked]>; Vignesh Raghavendra <[email-masked]>; Rob Herring
> > <[email-masked]>; David S. Miller <[email-masked]>; Jakub
> > Kicinski <[email-masked]>; Heiner Kallweit <[email-masked]>;
> > Russell King <[email-masked]>; Frank Rowand
> > <[email-masked]>; Boris Brezillon <[email-masked]>; linux-
> > [email-masked]; [email-masked]; linux-
> > [email-masked]; [email-masked]
> > Oggetto: Re: [PATCH v2 4/4] dt-bindings: net: Document use of mac-
> > address-increment
> > 
> > > +  mac-address-increment:
> > > +    description:
> > > +      The MAC address can optionally be increased (or decreased using
> > > +      negative values) from the original value readed (from a nvmem
> cell
> > 
> > Read is irregular, there is no readed, just read.
> > 
> > > +      for example). This can be used if the mac is readed from a
> dedicated
> > > +      partition and must be increased based on the number of device
> > > +      present in the system.
> > 
> > You should probably add there is no underflow/overflow to other bytes
> > of the MAC address. 00:01:02:03:04:ff + 1 == 00:01:02:03:04:00.
> > 
> > > +    minimum: -255
> > > +    maximum: 255
> > > +
> > > +  mac-address-increment-byte:
> > > +    description:
> > > +      If 'mac-address-increment' is defined, this will tell what byte
> of
> > > +      the mac-address will be increased. If 'mac-address-increment' is
> > > +      not defined, this option will do nothing.
> > > +    default: 5
> > > +    minimum: 0
> > > +    maximum: 5
> > 
> > Is there a real need for this? A value of 0 seems like a bad idea,
> > since a unicast address could easily become a multicast address, which
> > is not valid for an interface address. It also does not seem like a
> > good idea to allow the OUI to be changed. So i think only bytes 3-5
> > should be allowed, but even then, i don't think this is needed, unless
> > you do have a clear use case.
> > 
> >     Andrew
> 
> Honestly the mac-address-increment-byte is added to give user some control
> but I
> don't really have a use case for it. Should I limit it to 3 or just remove
> the function?

If you have no use case, just remove it and document that last byte
will be incremented. I somebody does need it, it can be added in a
backwards compatible way.

     Andrew