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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.
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:
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:
mdio {
phy0: ethernet-phy@0 {
rxc-skew-ps = <3000>;
rxdv-skew-ps = <0>;
txc-skew-ps = <3000>;
txen-skew-ps = <0>;
reg = <0>;
};
};
ethernet@70000 {
phy = <&phy0>;
phy-mode = "rgmii-id";
};
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