Re: FEC unbind/bind feature

On Thu, Mar 25, 2021 at 08:04:58AM +0000, Joakim Zhang wrote:

Hi Andrew, Florian, Heiner

You are all Ethernet MDIO bus and PHY experts, I have some questions may need your help, thanks a lot in advance.

For many board designs, if it has dual MAC instances, they always share one MDIO bus to save PINs. Such as, i.MX6UL EVK board:

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&fec1 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_enet1>;
	phy-mode = "rmii";
	phy-handle = <&ethphy0>;
	phy-supply = <&reg_peri_3v3>;
	status = "okay";
};

&fec2 {
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_enet2>;
	phy-mode = "rmii";
	phy-handle = <&ethphy1>;
	phy-supply = <&reg_peri_3v3>;
	status = "okay";

	mdio {
		#address-cells = <1>;
		#size-cells = <0>;

		ethphy0: ethernet-phy@2 {
			compatible = "ethernet-phy-id0022.1560";
			reg = <2>;
			micrel,led-mode = <1>;
			clocks = <&clks IMX6UL_CLK_ENET_REF>;
			clock-names = "rmii-ref";

		};

		ethphy1: ethernet-phy@1 {
			compatible = "ethernet-phy-id0022.1560";
			reg = <1>;
			micrel,led-mode = <1>;
			clocks = <&clks IMX6UL_CLK_ENET2_REF>;
			clock-names = "rmii-ref";
		};
	};
};

For FEC driver now, there is a patch from Fabio to prevent unbind/bind feature since dual FEC controllers share one MDIO bus. (https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/net/ethernet/freescale/fec_main.c?h=next-20210324&id=272bb0e9e8cdc76e04baeefa0cd43019daa0841b)
If we unbind fec2 and then fec1 can't work since MDIO bus is controlled by FEC1, FEC2 can't use it independently.

My question is that if we want to implement unbind/bind feature, what need we do?

One option is you unbind FEC1 first, and then FEC2.

It seems to abstract an independent MDIO bus for dual FEC
instances. I look at the MDIO dt bindings, it seems support such
case as it has "reg"
property. (Documentation/devicetree/bindings/net/mdio.yaml)

You can have fully standalone MDIO bus drivers. You generally do this
when the MDIO bus registers are in their own address space, which you
can ioremap() separately from the MAC registers. Take a look in
drivers/net/mdio/.

From your opinions, do you think it is necessary to improve it?

What is you use case for unbinding/binding the FEC?

     Andrew