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

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Message-ID: <38ae4ceb-da21-d73e-9625-1918b4ab4e16@linaro.org>
Date:   Wed, 17 May 2023 10:36:42 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Ivan Mikhaylov <fr0st61te@...il.com>,
        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 16/05/2023 13:47, Ivan Mikhaylov wrote:
hy 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?
>>
>> To my understanding, decision to add some numbers to MAC address does
>> not look like DT property at all. Otherwise please help me to
>> understand
>> - why different boards with same device should have different
>> offset/value?
>>
>> Anyway, commit msg also lacks any justification for this.
>>
>> Best regards,
>> Krzysztof
>>
> 
> Krzysztof, essentially some PCIe network cards have like an additional
> *MII interface which connects directly to a BMC (separate SoC for
> managing a motherboard) and by sending special ethernet type frames
> over that connection (called NC-SI) the BMC can obtain MAC, get link
> parameters etc. So it's natural for a vendor to allocate two MACs per
> such a board with PCIe card intergrated, with one MAC "flashed into"
> the network card, under the assumption that the BMC should

Who makes the assumption that next MAC should differ by 1 or 2?

> automatically use the next MAC. So it's the property of the hardware as
> the vendor designs it, not a matter of usage policy.
> 
> Also at the nvmem binding tree is "nvmem-cell-cells" which is literally
> the same as what was proposed but on different level.
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/Documentation/devicetree/bindings/nvmem?id=7e2805c203a6c8dc85c1cfda205161ed39ae82d5

How is this similar? This points the location of mac address on some NV
storage. You add fixed value which should be added to the Ethernet.

I might be missing the context but there is no DTS example nor user of
this property, so how can I get such?

Best regards,
Krzysztof