staging: mt7621-eth: Document ralink/mediatek SoC ethernet binding

Add possible dt binding for mediatek gigabit switches.
Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Michael Lee <igvtee@gmail.com>
Cc: devicetree@vger.kernel.org
Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/mt7621-eth/Documentation/devicetree/bindings/net/mediatek-net-gsw.txt

+Mediatek Gigabit Switch
+=======================
+
+The mediatek gigabit switch can be found on Mediatek SoCs.
+
+Required properties:
+- compatible: Should be "mediatek,mt7620-gsw", "mediatek,mt7621-gsw",
+  "mediatek,mt7623-gsw"
+- reg: Address and length of the register set for the device
+- interrupts: Should contain the gigabit switches interrupt
+
+
+Additional required properties for ARM based SoCs:
+- mediatek,reset-pin: phandle describing the reset GPIO
+- clocks: the clocks used by the switch
+- clock-names: the names of the clocks listed in the clocks property
+  these should be "trgpll", "esw", "gp2", "gp1"
+- mt7530-supply: the phandle of the regulator used to power the switch
+- mediatek,pctl-regmap: phandle to the port control regmap. this is used to
+  setup the drive current
+
+
+Optional properties:
+- interrupt-parent: Should be the phandle for the interrupt controller
+  that services interrupts for this device
+
+Example:
+
+gsw: switch@1b100000 {
+	compatible = "mediatek,mt7623-gsw";
+	reg = <0 0x1b110000 0 0x300000>;
+
+	interrupt-parent = <&pio>;
+	interrupts = <168 IRQ_TYPE_EDGE_RISING>;
+
+	clocks = <&apmixedsys CLK_APMIXED_TRGPLL>,
+		 <&ethsys CLK_ETHSYS_ESW>,
+		 <&ethsys CLK_ETHSYS_GP2>,
+		 <&ethsys CLK_ETHSYS_GP1>;
+	clock-names = "trgpll", "esw", "gp2", "gp1";
+
+	mt7530-supply = <&mt6323_vpa_reg>;
+
+	mediatek,pctl-regmap = <&syscfg_pctl_a>;
+	mediatek,reset-pin = <&pio 15 0>;
+
+	status = "okay";
+};

drivers/staging/mt7621-eth/TODO

+
+- verify devicetree documentation is consistent with code
+
+Cc: NeilBrown <neil@brown.name>