On Thu, Sep 14, 2017 at 2:19 PM, Andrew Lunn [off-list ref] wrote:

quoted

quoted

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 at lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel