doc: bindings: add mdio.txt describing generic MDIO properties

Adds a binding document for mdio.  A notable deviation from corresponding
Linux binding is the introduction of device-name optional property, which
can be used to name MDIO buses.  Two reset optional properties described
by Linux binding are also not present as they don't seem to be used in
U-Boot at this time.

Signed-off-by: Alex Marginean <alexm.osslist@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Alex Marginean <alexm.osslist@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

diff --git a/doc/device-tree-bindings/net/mdio.txt b/doc/device-tree-bindings/net/mdio.txt
new file mode 100644 (file)
index 0000000..1595325
--- /dev/null
+++ b/doc/device-tree-bindings/net/mdio.txt
@@ -0,0 +1,36 @@
+Common MDIO bus properties.
+
+These are generic properties that can apply to any MDIO bus.
+
+Optional properties:
+       - device-name - If present it is used to name the device and MDIO bus.
+                       The name must be unique and must not contain spaces.
+
+A list of child nodes, one per device on the bus is expected.  These could be
+PHYs, switches or similar devices and child nodes should follow the specific
+binding for the device type.
+
+Example :
+This example shows the structure used for the external MDIO bus on NXP LS1028A
+RDB board.  Note that this MDIO device is an integrated PCI function and
+requires no compatible property for probing.
+
+/* definition in SoC dtsi file */
+       pcie@1f0000000 {
+
+               mdio0: pci@0,3 {
+                       #address-cells=<0>;
+                       #size-cells=<1>;
+                       reg = <0x000300 0 0 0 0>;
+                       status = "disabled";
+                       device-name = "emdio";
+               };
+       };
+/* definition of PHYs in RDB dts file */
+&mdio0 {
+       status = "okay";
+       rdb_phy0: phy@2 {
+               reg = <2>;
+       };
+};
+