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.