Micrel KSZ9021/KSZ9031 Gigabit Ethernet PHY
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Some boards require special tuning values, particularly when it comes to
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clock delays. You can specify clock delay values by adding
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micrel-specific properties to an Ethernet OF device node.
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Note that these settings are applied after any phy-specific fixup from
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phy_fixup_list (see phy_init_hw() from drivers/net/phy/phy_device.c),
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and therefore may overwrite them.
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KSZ9021:
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All skew control options are specified in picoseconds. The minimum
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value is 0, the maximum value is 1800, and it is incremented by 120ps
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steps.
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Optional properties:
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- rxc-skew-ps : Skew control of RXC pad
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- rxdv-skew-ps : Skew control of RX CTL pad
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- txc-skew-ps : Skew control of TXC pad
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- txen-skew-ps : Skew control of TX CTL pad
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- rxd0-skew-ps : Skew control of RX data 0 pad
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- rxd1-skew-ps : Skew control of RX data 1 pad
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- rxd2-skew-ps : Skew control of RX data 2 pad
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- rxd3-skew-ps : Skew control of RX data 3 pad
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- txd0-skew-ps : Skew control of TX data 0 pad
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- txd1-skew-ps : Skew control of TX data 1 pad
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- txd2-skew-ps : Skew control of TX data 2 pad
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- txd3-skew-ps : Skew control of TX data 3 pad
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KSZ9031:
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All skew control options are specified in picoseconds. The minimum
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value is 0, and the maximum is property-dependent. The increment
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step is 60ps.
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The KSZ9031 hardware supports a range of skew values from negative to
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positive, where the specific range is property dependent. All values
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specified in the devicetree are offset by the minimum value so they
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can be represented as positive integers in the devicetree since it's
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difficult to represent a negative number in the devictree.
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The following 5-bit values table apply to rxc-skew-ps and txc-skew-ps.
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Pad Skew Value Delay (ps) Devicetree Value
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------------------------------------------------------
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0_0000 -900ps 0
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0_0001 -840ps 60
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0_0010 -780ps 120
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0_0011 -720ps 180
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0_0100 -660ps 240
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0_0101 -600ps 300
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0_0110 -540ps 360
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0_0111 -480ps 420
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0_1000 -420ps 480
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0_1001 -360ps 540
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0_1010 -300ps 600
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0_1011 -240ps 660
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0_1100 -180ps 720
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0_1101 -120ps 780
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0_1110 -60ps 840
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0_1111 0ps 900
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1_0000 60ps 960
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1_0001 120ps 1020
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1_0010 180ps 1080
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1_0011 240ps 1140
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1_0100 300ps 1200
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1_0101 360ps 1260
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1_0110 420ps 1320
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1_0111 480ps 1380
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1_1000 540ps 1440
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1_1001 600ps 1500
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1_1010 660ps 1560
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1_1011 720ps 1620
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1_1100 780ps 1680
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1_1101 840ps 1740
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1_1110 900ps 1800
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1_1111 960ps 1860
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The following 4-bit values table apply to the txdX-skew-ps, rxdX-skew-ps
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data pads, and the rxdv-skew-ps, txen-skew-ps control pads.
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Pad Skew Value Delay (ps) Devicetree Value
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------------------------------------------------------
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0000 -420ps 0
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0001 -360ps 60
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0010 -300ps 120
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0011 -240ps 180
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0100 -180ps 240
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0101 -120ps 300
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0110 -60ps 360
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0111 0ps 420
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1000 60ps 480
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1001 120ps 540
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1010 180ps 600
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1011 240ps 660
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1100 300ps 720
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1101 360ps 780
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1110 420ps 840
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1111 480ps 900
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Optional properties:
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Maximum value of 1860:
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- rxc-skew-ps : Skew control of RX clock pad
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- txc-skew-ps : Skew control of TX clock pad
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Maximum value of 900:
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- rxdv-skew-ps : Skew control of RX CTL pad
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- txen-skew-ps : Skew control of TX CTL pad
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- rxd0-skew-ps : Skew control of RX data 0 pad
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- rxd1-skew-ps : Skew control of RX data 1 pad
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- rxd2-skew-ps : Skew control of RX data 2 pad
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- rxd3-skew-ps : Skew control of RX data 3 pad
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- txd0-skew-ps : Skew control of TX data 0 pad
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- txd1-skew-ps : Skew control of TX data 1 pad
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- txd2-skew-ps : Skew control of TX data 2 pad
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- txd3-skew-ps : Skew control of TX data 3 pad
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Examples:
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/* Attach to an Ethernet device with autodetected PHY */
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&enet {
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rxc-skew-ps = <1800>;
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rxdv-skew-ps = <0>;
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txc-skew-ps = <1800>;
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txen-skew-ps = <0>;
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status = "okay";
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};
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/* Attach to an explicitly-specified PHY */
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mdio {
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phy0: ethernet-phy@0 {
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rxc-skew-ps = <1800>;
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rxdv-skew-ps = <0>;
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txc-skew-ps = <1800>;
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txen-skew-ps = <0>;
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reg = <0>;
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};
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};
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ethernet@70000 {
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status = "okay";
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phy = <&phy0>;
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phy-mode = "rgmii-id";
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};
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References
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Micrel ksz9021rl/rn Data Sheet, Revision 1.2. Dated 2/13/2014.
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http://www.micrel.com/_PDF/Ethernet/datasheets/ksz9021rl-rn_ds.pdf
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Micrel ksz9031rnx Data Sheet, Revision 2.1. Dated 11/20/2014.
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http://www.micrel.com/_PDF/Ethernet/datasheets/KSZ9031RNX.pdf
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Notes:
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Note that a previous version of the Micrel ksz9021rl/rn Data Sheet
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was missing extended register 106 (transmit data pad skews), and
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incorrectly specified the ps per step as 200ps/step instead of
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120ps/step. The latest update to this document reflects the latest
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revision of the Micrel specification even though usage in the kernel
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still reflects that incorrect document.
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