> - Providing no compatible for an MDIO child node is considered to be equivalent
> to a c22 ethernet phy, so one must be provided. However, this node is then
> not automatically probed.
It cannot be automatically probed, since register 2 and 3 do not
contain an ID, which PHYs do. So you need to explicitly list in on the
MDIO bus, and when the of_mdiobus_register() is called, the device
will be instantiated.
Is it okay to provide a binding without a driver?
> If some code is required, where should this be put?
> Current devicetree structure:
> mdio-bus {
> compatible = "vendor,mdio";
> ...
>
> expander0: expander@0 {
> /*
> * Provide compatible for working registration of mdio device.
> * Device probing happens in gpio1 node.
> */
> compatible = "realtek,rtl8231-expander";
> reg = <0>;
> };
>
> };
> gpio1 : ext_gpio {
> compatible = "realtek,rtl8231-mdio";
> gpio-controller;
> ...
> };
I don't understand this split. Why not
mdio-bus {
compatible = "vendor,mdio";
...
expander0: expander@0 {
/*
* Provide compatible for working registration of mdio device.
* Device probing happens in gpio1 node.
*/
compatible = "realtek,rtl8231-expander";
reg = <0>;
gpio-controller;
};
};
You can list whatever properties you need in the node. Ethernet
switches have interrupt-controller, embedded MDIO busses with PHYs on
them etc.
> - MFD driver:
> The RTL8231 is not just a GPIO expander, but also a pin controller and LED
> matrix controller. Regmap initialisation could probably be moved to a parent
> MFD, with gpio, led, and pinctrl cells. Is this a hard requirement if only a
> GPIO controller is provided?
You need to think about forward/backwards compatibility. You are
defining a binding now, which you need to keep. Do you see how an MFD
could be added without breaking backwards compatibility?
Andrew
