linux-kernel - Re: [PATCH 2/2] dt-bindings: net: dsa: mediatek,mt7530: document MDIO-bus

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Date:   Sun, 30 Apr 2023 13:44:12 +0100
From:   Daniel Golle <daniel@...rotopia.org>
To:     Arınç ÜNAL <arinc.unal@...nc9.com>
Cc:     David Bauer <mail@...id-bauer.net>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...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>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Sean Wang <sean.wang@...iatek.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 2/2] dt-bindings: net: dsa: mediatek,mt7530: document
 MDIO-bus

On Sun, Apr 30, 2023 at 03:34:43PM +0300, Arınç ÜNAL wrote:
> On 30.04.2023 14:28, David Bauer wrote:
> > Document the ability to add nodes for the MDIO bus connecting the
> > switch-internal PHYs.
> 
> This is quite interesting. Currently the PHY muxing feature for the MT7530
> switch looks for some fake ethernet-phy definitions on the mdio-bus where
> the switch is also defined.
> 
> Looking at the binding here, there will be an mdio node under the switch
> node. This could be useful to define the ethernet-phys for PHY muxing here
> instead, so we don't waste the register addresses on the parent mdio-bus for
> fake things. It looks like this should work right out of the box. I will do
> some tests.
> 
> Are there any examples as to what to configure on the switch PHYs with this
> change?
> 
> > 
> > Signed-off-by: David Bauer <mail@...id-bauer.net>
> > ---
> >   .../devicetree/bindings/net/dsa/mediatek,mt7530.yaml        | 6 ++++++
> >   1 file changed, 6 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.yaml b/Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.yaml
> > index e532c6b795f4..50f8f83cc440 100644
> > --- a/Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.yaml
> > +++ b/Documentation/devicetree/bindings/net/dsa/mediatek,mt7530.yaml
> > @@ -128,6 +128,12 @@ properties:
> >         See Documentation/devicetree/bindings/regulator/mt6323-regulator.txt for
> >         details for the regulator setup on these boards.
> > +  mdio:
> > +    $ref: /schemas/net/mdio.yaml#
> > +    unevaluatedProperties: false
> > +    description:
> > +      Node for the internal MDIO bus connected to the embedded ethernet-PHYs.
> 
> Please set this property as false for mediatek,mt7988-switch as it doesn't
> use MDIO.

Well, quite the opposite is true. This change is **needed** on MT7988 as
the built-in 1GE PHYs of the MT7988 are connected to the (internal) MDIO
bus of the switch. And they do need calibration data assigned as nvmem
via device tree.

tl;dr: Despite not being connected via MDIO itself also MT7988 exposes an
internal MDIO bus for the switch PHYs.