Micrel KSZ9021/KSZ9031 Gigabit Ethernet PHY

Some boards require special tuning values, particularly when it comes
to clock delays. You can specify clock delay values in the PHY OF
device node. Deprecated, but still supported, these properties can
also be added to an Ethernet OF device node.

Note that these settings are applied after any phy-specific fixup from
phy_fixup_list (see phy_init_hw() from drivers/net/phy/phy_device.c),
and therefore may overwrite them.

KSZ9021:

  All skew control options are specified in picoseconds. The minimum
  value is 0, the maximum value is 3000, and it is incremented by 200ps
  steps.

  Optional properties:

    - rxc-skew-ps : Skew control of RXC pad
    - rxdv-skew-ps : Skew control of RX CTL pad
    - txc-skew-ps : Skew control of TXC pad
    - txen-skew-ps : Skew control of TX CTL pad
    - rxd0-skew-ps : Skew control of RX data 0 pad
    - rxd1-skew-ps : Skew control of RX data 1 pad
    - rxd2-skew-ps : Skew control of RX data 2 pad
    - rxd3-skew-ps : Skew control of RX data 3 pad
    - txd0-skew-ps : Skew control of TX data 0 pad
    - txd1-skew-ps : Skew control of TX data 1 pad
    - txd2-skew-ps : Skew control of TX data 2 pad
    - txd3-skew-ps : Skew control of TX data 3 pad

KSZ9031:

  All skew control options are specified in picoseconds. The minimum
  value is 0, and the maximum is property-dependent. The increment
  step is 60ps. The default value is the neutral setting, so setting
  rxc-skew-ps=<0> actually results in -900 picoseconds adjustment.

  Optional properties:

    Maximum value of 1860, default value 900:

      - rxc-skew-ps : Skew control of RX clock pad
      - txc-skew-ps : Skew control of TX clock pad

    Maximum value of 900, default value 420:

      - rxdv-skew-ps : Skew control of RX CTL pad
      - txen-skew-ps : Skew control of TX CTL pad
      - rxd0-skew-ps : Skew control of RX data 0 pad
      - rxd1-skew-ps : Skew control of RX data 1 pad
      - rxd2-skew-ps : Skew control of RX data 2 pad
      - rxd3-skew-ps : Skew control of RX data 3 pad
      - txd0-skew-ps : Skew control of TX data 0 pad
      - txd1-skew-ps : Skew control of TX data 1 pad
      - txd2-skew-ps : Skew control of TX data 2 pad
      - txd3-skew-ps : Skew control of TX data 3 pad

Examples:

	mdio {
		phy0: ethernet-phy@0 {
			rxc-skew-ps = <3000>;
			rxdv-skew-ps = <0>;
			txc-skew-ps = <3000>;
			txen-skew-ps = <0>;
			reg = <0>;
		};
	};
	ethernet@70000 {
		phy = <&phy0>;
		phy-mode = "rgmii-id";
	};
