dsa driver for mv88e61xx

[Tim Harvey]

Greetings,

I wanted to take a stab at adding dsa support for the mv88e61xx which
currently has a driver in drivers/net/phy [1]. The board I have
available to me is the gw5904 which has a mv88e6085 with the upstream
port connected to the IMX6 FEC MAC over RGMII. This currently works
with the existing mv88e61xx driver with the following defined in
gwventana_gw5904_defconfig:

CONFIG_MV88E61XX_SWITCH=y
CONFIG_MV88E61XX_CPU_PORT=5
CONFIG_MV88E61XX_PHY_PORTS=0xf
CONFIG_MV88E61XX_FIXED_PORTS=0x0

The device-tree is arch/arm/dts/imx6qdl-gw5904.dtsi [2] which I
believe is proper and works in Linux with the Linux driver in
drivers/net/dsa/mv88e6xxx [3].

&fec {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_enet>;
        phy-mode = "rgmii-id";
        phy-reset-gpios = <&gpio1 30 GPIO_ACTIVE_LOW>;
        phy-reset-duration = <10>;
        phy-reset-post-delay = <100>;
        status = "okay";

        fixed-link {
                speed = <1000>;
                full-duplex;
        };

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

                switch at 0 {
                        compatible = "marvell,mv88e6085";
                        reg = <0>;

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

                                port at 0 {
                                        reg = <0>;
                                        label = "lan4";
                                };

                                port at 1 {
                                        reg = <1>;
                                        label = "lan3";
                                };

                                port at 2 {
                                        reg = <2>;
                                        label = "lan2";
                                };

                                port at 3 {
                                        reg = <3>;
                                        label = "lan1";
                                };

                                port at 5 {
                                        reg = <5>;
                                        label = "cpu";
                                        ethernet = <&fec>;
                                };
                        };
                };
        };
};

My motivation for doing this is to be able to drop
gwventana_gw5904_defconfig as it is the same defconfig as
gwventana_emmc_defconfig with the switch added and with get_phy_id
overridden by the current mv88e61xx driver that config won't work with
boards that lack the switch.

My first approach was to just put a #if !defined(CONFIG_DM_DSA) around
mv88e61xx get_phy_id and add a skeleton driver with an of_match of
compatible = "marvell,mv88e6085" but the driver does not probe with
the above dt fragment.

Any ideas why the driver won't probe and advise on how I should
proceed with this? I'm not clear yet if I can just modify the existing
driver or if I should create a new one.

Best Regards,

Tim
[1] https://elixir.bootlin.com/u-boot/latest/source/drivers/net/phy/mv88e61xx.c
[2] https://elixir.bootlin.com/u-boot/latest/source/arch/arm/dts/imx6qdl-gw5904.dtsi
[3] https://elixir.bootlin.com/linux/latest/source/drivers/net/dsa/mv88e6xxx/chip.c