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

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Message-ID: <20200920012216.GE3673389@lunn.ch>
Date:   Sun, 20 Sep 2020 03:22:16 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     ansuelsmth@...il.com
Cc:     'Miquel Raynal' <miquel.raynal@...tlin.com>,
        'Richard Weinberger' <richard@....at>,
        'Vignesh Raghavendra' <vigneshr@...com>,
        'Rob Herring' <robh+dt@...nel.org>,
        "'David S. Miller'" <davem@...emloft.net>,
        'Jakub Kicinski' <kuba@...nel.org>,
        'Heiner Kallweit' <hkallweit1@...il.com>,
        'Russell King' <linux@...linux.org.uk>,
        'Frank Rowand' <frowand.list@...il.com>,
        'Boris Brezillon' <bbrezillon@...nel.org>,
        linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: R: [PATCH v2 4/4] dt-bindings: net: Document use of
 mac-address-increment

On Sun, Sep 20, 2020 at 02:39:39AM +0200, ansuelsmth@...il.com wrote:
> 
> 
> > -----Messaggio originale-----
> > Da: Andrew Lunn <andrew@...n.ch>
> > Inviato: domenica 20 settembre 2020 02:31
> > A: Ansuel Smith <ansuelsmth@...il.com>
> > Cc: Miquel Raynal <miquel.raynal@...tlin.com>; Richard Weinberger
> > <richard@....at>; Vignesh Raghavendra <vigneshr@...com>; Rob Herring
> > <robh+dt@...nel.org>; David S. Miller <davem@...emloft.net>; Jakub
> > Kicinski <kuba@...nel.org>; Heiner Kallweit <hkallweit1@...il.com>;
> > Russell King <linux@...linux.org.uk>; Frank Rowand
> > <frowand.list@...il.com>; Boris Brezillon <bbrezillon@...nel.org>; linux-
> > mtd@...ts.infradead.org; devicetree@...r.kernel.org; linux-
> > kernel@...r.kernel.org; netdev@...r.kernel.org
> > 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