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    SubjectRe: [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@lunn.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@lists.infradead.org
    > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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