This is the default mt7621 dts file used by all mt7621 devices, creating a corresponding dtsi matching your new device with the overriding settings required.
switch0: switch@1f {
compatible = "mediatek,mt7621";
#address-cells = <1>;
#size-cells = <0>;
reg = <0x1f>;
mediatek,mcm;
resets = <&rstctrl 2>;
reset-names = "mcm";
ports {
#address-cells = <1>;
#size-cells = <0>;
reg = <0>;
port@0 {
status = "disabled";
reg = <0>;
label = "lan0";
};
port@1 {
status = "disabled";
reg = <1>;
label = "lan1";
};
port@2 {
status = "disabled";
reg = <2>;
label = "lan2";
};
port@3 {
status = "disabled";
reg = <3>;
label = "lan3";
};
port@4 {
status = "disabled";
reg = <4>;
label = "lan4";
};
port@6 {
reg = <6>;
label = "cpu";
ethernet = <&gmac0>;
phy-mode = "rgmii";
fixed-link {
speed = <1000>;
full-duplex;
};
};
};
Just override on the port 6, so remove full-duplex and pause etc