--- /dev/null
+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 by adding
+micrel-specific properties 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 1800, and it is incremented by 120ps
+ 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 KSZ9031 hardware supports a range of skew values from negative to
+ positive, where the specific range is property dependent. All values
+ specified in the devicetree are offset by the minimum value so they
+ can be represented as positive integers in the devicetree since it's
+ difficult to represent a negative number in the devictree.
+
+ The following 5-bit values table apply to rxc-skew-ps and txc-skew-ps.
+
+ Pad Skew Value Delay (ps) Devicetree Value
+ ------------------------------------------------------
+ 0_0000 -900ps 0
+ 0_0001 -840ps 60
+ 0_0010 -780ps 120
+ 0_0011 -720ps 180
+ 0_0100 -660ps 240
+ 0_0101 -600ps 300
+ 0_0110 -540ps 360
+ 0_0111 -480ps 420
+ 0_1000 -420ps 480
+ 0_1001 -360ps 540
+ 0_1010 -300ps 600
+ 0_1011 -240ps 660
+ 0_1100 -180ps 720
+ 0_1101 -120ps 780
+ 0_1110 -60ps 840
+ 0_1111 0ps 900
+ 1_0000 60ps 960
+ 1_0001 120ps 1020
+ 1_0010 180ps 1080
+ 1_0011 240ps 1140
+ 1_0100 300ps 1200
+ 1_0101 360ps 1260
+ 1_0110 420ps 1320
+ 1_0111 480ps 1380
+ 1_1000 540ps 1440
+ 1_1001 600ps 1500
+ 1_1010 660ps 1560
+ 1_1011 720ps 1620
+ 1_1100 780ps 1680
+ 1_1101 840ps 1740
+ 1_1110 900ps 1800
+ 1_1111 960ps 1860
+
+ The following 4-bit values table apply to the txdX-skew-ps, rxdX-skew-ps
+ data pads, and the rxdv-skew-ps, txen-skew-ps control pads.
+
+ Pad Skew Value Delay (ps) Devicetree Value
+ ------------------------------------------------------
+ 0000 -420ps 0
+ 0001 -360ps 60
+ 0010 -300ps 120
+ 0011 -240ps 180
+ 0100 -180ps 240
+ 0101 -120ps 300
+ 0110 -60ps 360
+ 0111 0ps 420
+ 1000 60ps 480
+ 1001 120ps 540
+ 1010 180ps 600
+ 1011 240ps 660
+ 1100 300ps 720
+ 1101 360ps 780
+ 1110 420ps 840
+ 1111 480ps 900
+
+ Optional properties:
+
+ Maximum value of 1860:
+
+ - rxc-skew-ps : Skew control of RX clock pad
+ - txc-skew-ps : Skew control of TX clock pad
+
+ Maximum value of 900:
+
+ - 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:
+
+ /* Attach to an Ethernet device with autodetected PHY */
+ &enet {
+ rxc-skew-ps = <1800>;
+ rxdv-skew-ps = <0>;
+ txc-skew-ps = <1800>;
+ txen-skew-ps = <0>;
+ status = "okay";
+ };
+
+ /* Attach to an explicitly-specified PHY */
+ mdio {
+ phy0: ethernet-phy@0 {
+ rxc-skew-ps = <1800>;
+ rxdv-skew-ps = <0>;
+ txc-skew-ps = <1800>;
+ txen-skew-ps = <0>;
+ reg = <0>;
+ };
+ };
+ ethernet@70000 {
+ status = "okay";
+ phy = <&phy0>;
+ phy-mode = "rgmii-id";
+ };
+
+References
+
+ Micrel ksz9021rl/rn Data Sheet, Revision 1.2. Dated 2/13/2014.
+ http://www.micrel.com/_PDF/Ethernet/datasheets/ksz9021rl-rn_ds.pdf
+
+ Micrel ksz9031rnx Data Sheet, Revision 2.1. Dated 11/20/2014.
+ http://www.micrel.com/_PDF/Ethernet/datasheets/KSZ9031RNX.pdf
+
+Notes:
+
+ Note that a previous version of the Micrel ksz9021rl/rn Data Sheet
+ was missing extended register 106 (transmit data pad skews), and
+ incorrectly specified the ps per step as 200ps/step instead of
+ 120ps/step. The latest update to this document reflects the latest
+ revision of the Micrel specification even though usage in the kernel
+ still reflects that incorrect document.
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