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.