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+Micrel KSZ9021/KSZ9031/KSZ9131 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 can be specified in 200ps
+ steps, *but* these values are in not fact what you get because this chip's
+ skew values actually increase in 120ps steps, starting from -840ps. The
+ incorrect values came from an error in the original KSZ9021 datasheet
+ before it was corrected in revision 1.2 (Feb 2014), but it is too late to
+ change the driver now because of the many existing device trees that have
+ been created using values that go up in increments of 200.
+
+ The following table shows the actual skew delay you will get for each of the
+ possible devicetree values, and the number that will be programmed into the
+ corresponding pad skew register:
+
+ Device Tree Value Delay Pad Skew Register Value
+ -----------------------------------------------------
+ 0 -840ps 0000
+ 200 -720ps 0001
+ 400 -600ps 0010
+ 600 -480ps 0011
+ 800 -360ps 0100
+ 1000 -240ps 0101
+ 1200 -120ps 0110
+ 1400 0ps 0111
+ 1600 120ps 1000
+ 1800 240ps 1001
+ 2000 360ps 1010
+ 2200 480ps 1011
+ 2400 600ps 1100
+ 2600 720ps 1101
+ 2800 840ps 1110
+ 3000 960ps 1111
+
+ 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.
+
+ 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, 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
+
+ - micrel,force-master:
+ Boolean, force phy to master mode. Only set this option if the phy
+ reference clock provided at CLK125_NDO pin is used as MAC reference
+ clock because the clock jitter in slave mode is to high (errata#2).
+ Attention: The link partner must be configurable as slave otherwise
+ no link will be established.
+
+KSZ9131:
+LAN8841:
+
+ All skew control options are specified in picoseconds. The increment
+ step is 100ps. Unlike KSZ9031, the values represent picoseccond delays.
+ A negative value can be assigned as rxc-skew-psec = <(-100)>;.
+
+ Optional properties:
+
+ Range of the value -700 to 2400, default value 0:
+
+ - rxc-skew-psec : Skew control of RX clock pad
+ - txc-skew-psec : Skew control of TX clock pad
+
+ Range of the value -700 to 800, default value 0:
+
+ - rxdv-skew-psec : Skew control of RX CTL pad
+ - txen-skew-psec : Skew control of TX CTL pad
+ - rxd0-skew-psec : Skew control of RX data 0 pad
+ - rxd1-skew-psec : Skew control of RX data 1 pad
+ - rxd2-skew-psec : Skew control of RX data 2 pad
+ - rxd3-skew-psec : Skew control of RX data 3 pad
+ - txd0-skew-psec : Skew control of TX data 0 pad
+ - txd1-skew-psec : Skew control of TX data 1 pad
+ - txd2-skew-psec : Skew control of TX data 2 pad
+ - txd3-skew-psec : 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 {
+ 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.