Micrel KSZ9021/KSZ9031/KSZ9131 Gigabit Ethernet PHY
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Some boards require special tuning values, particularly when it comes
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to clock delays. You can specify clock delay values in the PHY OF
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device node. Deprecated, but still supported, these properties can
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also be added 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 3000, and it can be specified in 200ps
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steps, *but* these values are in not fact what you get because this chip's
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skew values actually increase in 120ps steps, starting from -840ps. The
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incorrect values came from an error in the original KSZ9021 datasheet
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before it was corrected in revision 1.2 (Feb 2014), but it is too late to
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change the driver now because of the many existing device trees that have
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been created using values that go up in increments of 200.
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The following table shows the actual skew delay you will get for each of the
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possible devicetree values, and the number that will be programmed into the
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corresponding pad skew register:
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Device Tree Value Delay Pad Skew Register Value
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-----------------------------------------------------
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0 -840ps 0000
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200 -720ps 0001
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400 -600ps 0010
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600 -480ps 0011
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800 -360ps 0100
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1000 -240ps 0101
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1200 -120ps 0110
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1400 0ps 0111
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1600 120ps 1000
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1800 240ps 1001
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2000 360ps 1010
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2200 480ps 1011
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2400 600ps 1100
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2600 720ps 1101
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2800 840ps 1110
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3000 960ps 1111
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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. The default value is the neutral setting, so setting
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rxc-skew-ps=<0> actually results in -900 picoseconds adjustment.
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Optional properties:
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Maximum value of 1860, default value 900:
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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, default value 420:
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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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- micrel,force-master:
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Boolean, force phy to master mode. Only set this option if the phy
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reference clock provided at CLK125_NDO pin is used as MAC reference
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clock because the clock jitter in slave mode is to high (errata#2).
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Attention: The link partner must be configurable as slave otherwise
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no link will be established.
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KSZ9131:
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All skew control options are specified in picoseconds. The increment
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step is 100ps. Unlike KSZ9031, the values represent picoseccond delays.
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A negative value can be assigned as rxc-skew-psec = <(-100)>;.
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Optional properties:
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Range of the value -700 to 2400, default value 0:
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- rxc-skew-psec : Skew control of RX clock pad
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- txc-skew-psec : Skew control of TX clock pad
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Range of the value -700 to 800, default value 0:
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- rxdv-skew-psec : Skew control of RX CTL pad
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- txen-skew-psec : Skew control of TX CTL pad
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- rxd0-skew-psec : Skew control of RX data 0 pad
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- rxd1-skew-psec : Skew control of RX data 1 pad
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- rxd2-skew-psec : Skew control of RX data 2 pad
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- rxd3-skew-psec : Skew control of RX data 3 pad
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- txd0-skew-psec : Skew control of TX data 0 pad
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- txd1-skew-psec : Skew control of TX data 1 pad
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- txd2-skew-psec : Skew control of TX data 2 pad
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- txd3-skew-psec : Skew control of TX data 3 pad
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Examples:
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mdio {
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phy0: ethernet-phy@0 {
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rxc-skew-ps = <3000>;
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rxdv-skew-ps = <0>;
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txc-skew-ps = <3000>;
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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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phy = <&phy0>;
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phy-mode = "rgmii-id";
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};
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