Related to this, I have a query on how the DT node for gmii2rgmii should look.
One of the users of gmii2rgmii is Cadence macb driver. In Xilinx tree, we use
this piece of code to register this mdiobus:
+ mdio_np = of_get_child_by_name(np, "mdio");
+ if (mdio_np) {
+ of_node_put(mdio_np);
+ err = of_mdiobus_register(bp->mii_bus, mdio_np);
+ if (err)
+ goto err_out_unregister_bus;

And the DT node looks like this:
ethernet {
    phy-mode = "gmii";
    phy-handle = <&extphy>;

    mdio {
        extphy {
            reg = <x>;
        };
        gmii_to_rgmii{
            compatible = "xlnx,gmii-to-rgmii-1.0";
            phy-handle = <&extphy>;
            reg = <x>;
        };
    };
};

Hi Harini

You have this setup:
  
MAC <==> GMII2RGMII <==> RGMII_PHY

So you want the MAC phy-handle to point to the gmii_to_rgmii 'PHY'.

Feel free to submit a patch extending
Documentation/devicetree/bindings/net/xilinx_gmii2rgmii.txt to include
a MAC node, etc.

   Andrew