linux-kernel - Re: [PATCH v5 05/10] dt-bindings: net: dwmac-sun8i: update documentation about integrated PHY

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Message-ID: <CAL_JsqJ2eVA9Zg60Hagqm732ZoOzHWTwVBqOabOhjE5aQ26L+g@mail.gmail.com>
Date:   Tue, 19 Sep 2017 21:49:52 -0500
From:   Rob Herring <robh@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Corentin Labbe <clabbe.montjoie@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chen-Yu Tsai <wens@...e.org>, netdev <netdev@...r.kernel.org>,
        Giuseppe CAVALLARO <peppe.cavallaro@...com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5 05/10] dt-bindings: net: dwmac-sun8i: update
 documentation about integrated PHY

On Thu, Sep 14, 2017 at 2:19 PM, Andrew Lunn <andrew@...n.ch> wrote:
>> > Is the MDIO controller "allwinner,sun8i-h3-emac" or "snps,dwmac-mdio"?
>> > If the latter, then I think the node is fine, but then the mux should be
>> > a child node of it. IOW, the child of an MDIO controller should either
>> > be a mux node or slave devices.
>
> Hi Rob
>
> Up until now, children of an MDIO bus have been MDIO devices. Those
> MDIO devices are either Ethernet PHYs, Ethernet Switches, or the
> oddball devices that Broadcom iProc has, like generic PHYs.
>
> We have never had MDIO-muxes as MDIO children. A Mux is not an MDIO
> device, and does not have the properties of an MDIO device. It is not
> addressable on the MDIO bus. The current MUXes are addressed via GPIOs
> or MMIO.

The DT parent/child relationship defines the bus topology. We describe
MDIO buses in that way and if a mux is sitting between the controller
and the devices, then the DT hierarchy should reflect that. Now
sometimes we have 2 options for what interface has the parent/child
relationship (e.g. an I2C controlled USB hub chip), but in this case
we don't.

> There other similar cases. i2c-mux-gpio is not a child of an i2c bus,
> nor i2c-mux-reg or gpio-mux. nxp,pca9548 is however a child of the i2c
> bus, because it is an i2c device itself...

Some are i2c controlled mux devices, but some can be GPIO controlled.

>
> If the MDIO mux was an MDIO device, i would agree with you. Bit it is
> not, so lets not make it a child.
>
>             Andrew
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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