linux-kernel - Re: [PATCH 2/4] dt-bindings: net: dsa: document internal MDIO bus

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Date:   Tue, 5 Sep 2023 14:00:21 +0300
From:   Arınç ÜNAL <arinc.unal@...nc9.com>
To:     Luiz Angelo Daros de Luca <luizluca@...il.com>
Cc:     Vladimir Oltean <olteanv@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.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>,
        Conor Dooley <conor+dt@...nel.org>,
        Woojung Huh <woojung.huh@...rochip.com>,
        UNGLinuxDriver@...rochip.com,
        Linus Walleij <linus.walleij@...aro.org>,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        Daniel Golle <daniel@...rotopia.org>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, mithat.guner@...ont.com,
        erkin.bozoglu@...ont.com, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 2/4] dt-bindings: net: dsa: document internal MDIO bus

On 5.09.2023 05:42, Luiz Angelo Daros de Luca wrote:
>>> [1] ...this. The SMI-controlled and MDIO-controlled Realtek switches are
>>> otherwise the same, right? So why would they have different dt-bindings?
>>
>> Honestly, I'm wondering the answer to this as well. For some reason, when
>> probing the SMI controlled Realtek switches, instead of just letting
>> dsa_switch_setup() populate ds->slave_mii_bus, on realtek_smi_setup_mdio()
>> on realtek-smi.c:
>>
>> - priv->slave_mii_bus is allocated.
>> - mdio_np = of_get_compatible_child(priv->dev->of_node, "realtek,smi-mdio");
>> - priv->slave_mii_bus->dev.of_node = mdio_np;
>> - ds->slave_mii_bus = priv->slave_mii_bus;
> 
> I might be able to help here. The Realtek SMI version created a custom
> slave_mii driver because it was the only way to associate it with an
> MDIO DT node. And that DT node was required to specify the interrupts
> for each phy0.
> It would work without that mdio node, letting DSA setup handle the
> slave bus, but it would rely only on polling for port status.
> 
> As we only have a single internal MDIO, the compatible string
> "realtek,smi-mdio" would not be necessary if the driver checks for a
> "mdio"-named child node. Maybe the code was just inspired by another
> DSA driver that uses more MDIO buses or external ones. The "mdio" name
> is suggested by docs since it was committed
> (https://www.kernel.org/doc/Documentation/devicetree/bindings/net/dsa/realtek-smi.txt).
> That name was also kept in the YAML translation
> (https://www.kernel.org/doc/Documentation/devicetree/bindings/net/dsa/realtek.yaml).
> 
> The Realtek MDIO driver was merged at the same release that included
> the change that allows dsa_switch_setup() to reference the "mdio"
> OF-node if present. That way, it could avoid creating a custom
> slave_mii_bus driver.
> 
> I submitted a small series of patches to unify that behavior between
> those two drivers:
> 
> https://lore.kernel.org/netdev/CAJq09z44SNGFkCi_BCpQ+3DuXhKfGVsMubRYE7AezJsGGOboVA@mail.gmail.com/
> (This is my answer to the series opening message to include the first
> paragraph ate by the editor)
> 
> There was some discussion but not NAC, ACK or RFC. It would have
> dropped some lines of code. I can revive it if there is interest.

I'd like this to happen, thanks Luiz!

Arınç