linux-kernel - Re: [PATCH v2 3/5] dt-bindings: net: add mac-address-increment option

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Message-ID: <be85bef7e144ebe08f422bf53bb81b59a130cb29.camel@gmail.com>
Date:   Fri, 12 May 2023 11:28:37 +0000
From:   Ivan Mikhaylov <fr0st61te@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Samuel Mendoza-Jonas <sam@...dozajonas.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, openbmc@...ts.ozlabs.org,
        Paul Fertser <fercerpav@...il.com>
Subject: Re: [PATCH v2 3/5] dt-bindings: net: add mac-address-increment
 option

On Fri, 2023-05-12 at 08:22 +0200, Krzysztof Kozlowski wrote:
> On 11/05/2023 01:31, Ivan Mikhaylov wrote:
> > On Wed, 2023-05-10 at 16:48 +0200, Krzysztof Kozlowski wrote:
> > > On 09/05/2023 16:35, Ivan Mikhaylov wrote:
> > > > Add the mac-address-increment option for specify MAC address
> > > > taken
> > > > by
> > > > any other sources.
> > > > 
> > > > Signed-off-by: Paul Fertser <fercerpav@...il.com>
> > > > Signed-off-by: Ivan Mikhaylov <fr0st61te@...il.com>
> > > > ---
> > > >  .../devicetree/bindings/net/ethernet-controller.yaml      | 8
> > > > ++++++++
> > > >  1 file changed, 8 insertions(+)
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/net/ethernet-
> > > > controller.yaml
> > > > b/Documentation/devicetree/bindings/net/ethernet-
> > > > controller.yaml
> > > > index 00be387984ac..6900098c5105 100644
> > > > --- a/Documentation/devicetree/bindings/net/ethernet-
> > > > controller.yaml
> > > > +++ b/Documentation/devicetree/bindings/net/ethernet-
> > > > controller.yaml
> > > > @@ -34,6 +34,14 @@ properties:
> > > >      minItems: 6
> > > >      maxItems: 6
> > > >  
> > > > +  mac-address-increment:
> > > > +    $ref: /schemas/types.yaml#/definitions/int32
> > > > +    description:
> > > > +      Specifies the MAC address increment to be added to the
> > > > MAC
> > > > address.
> > > > +      Should be used in cases when there is a need to use MAC
> > > > address
> > > > +      different from one obtained by any other level, like u-
> > > > boot
> > > > or the
> > > > +      NC-SI stack.
> > > 
> > > We don't store MAC addresses in DT, but provide simple
> > > placeholder
> > > for
> > > firmware or bootloader. Why shall we store static "increment"
> > > part of
> > > MAC address? Can't the firmware give you proper MAC address?
> > > 
> > > Best regards,
> > > Krzysztof
> > > 
> > 
> > Krzysztof, maybe that's a point to make commit message with better
> > explanation from my side. At current time there is at least two
> > cases
> > where I see it's possible to be used:
> > 
> > 1. NC-SI
> > 2. embedded
> > 
> > At NC-SI level there is Get Mac Address command which provides to
> > BMC
> > mac address from the host which is same as host mac address, it
> > happens
> > at runtime and overrides old one.
> > 
> > Also, this part was also to be discussed 2 years ago in this
> > thread:
> > https://lore.kernel.org/all/OF8E108F72.39D22E89-ON00258765.001E46EB-00258765.00251157@ibm.com/
> 
> Which was not sent to Rob though...
> 
> 
> > 
> > Where Milton provided this information:
> > 
> > DTMF spec DSP0222 NC-SI (network controller sideband interface)
> > is a method to provide a BMC (Baseboard management controller)
> > shared
> > access to an external ethernet port for comunication to the
> > management
> > network in the outside world.  The protocol describes ethernet
> > packets 
> > that control selective bridging implemented in a host network
> > controller
> > to share its phy.  Various NIC OEMs have added a query to find out
> > the 
> > address the host is using, and some vendors have added code to
> > query
> > host
> > nic and set the BMC mac to a fixed offset (current hard coded +1
> > from
> > the host value).  If this is compiled in the kernel, the NIC OEM is
> > recognised and the BMC doesn't miss the NIC response the address is
> > set
> > once each time the NCSI stack reinitializes.  This mechanism
> > overrides
> > any mac-address or local-mac-address or other assignment.
> > 
> > DSP0222
> > https://www.dmtf.org/documents/pmci/network-controller-sideband-interface-nc-si-specification-110
> > 
> > 
> > In embedded case, sometimes you have different multiple ethernet
> > interfaces which using one mac address which increments or
> > decrements
> > for particular interface, just for better explanation, there is
> > patch
> > with explanation which providing them such way of work:
> > https://github.com/openwrt/openwrt/blob/master/target/linux/generic/pending-5.15/682-of_net-add-mac-address-increment-support.patch
> > 
> > In their rep a lot of dts using such option.
> 
> None of these explain why this is property of the hardware. I
> understand
> that this is something you want Linux to do, but DT is not for that
> purpose. Do not encode system policies into DT and what above commit
> says is a policy.
> 

Krzysztof, okay then to which DT subsystem it should belong? To
ftgmac100 after conversion?

Thanks.