net: phy: micrel: Use correct skew values on KSZ9021

[platform/kernel/u-boot.git] / doc / device-tree-bindings / net / micrel-ksz90x1.txt

diff --git a/doc/device-tree-bindings/net/micrel-ksz90x1.txt b/doc/device-tree-bindings/net/micrel-ksz90x1.txt
index 307f53f..a214d35 100644 (file)
--- a/doc/device-tree-bindings/net/micrel-ksz90x1.txt
+++ b/doc/device-tree-bindings/net/micrel-ksz90x1.txt
@@ -14,6 +14,33 @@ KSZ9021:
   value is 0, the maximum value is 1800, and it is incremented by 120ps
   steps.
 
+  The KSZ9021 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 4-bit values table applies to all the skew properties:
+
+  Pad Skew Value       Delay (ps)      Devicetree Value
+  ------------------------------------------------------
+  0000                 -840ps          0
+  0001                 -720ps          120
+  0010                 -600ps          240
+  0011                 -480ps          360
+  0100                 -360ps          480
+  0101                 -240ps          600
+  0110                 -120ps          720
+  0111                 0ps             840
+  1000                 120ps           960
+  1001                 240ps           1080
+  1010                 360ps           1200
+  1011                 480ps           1320
+  1100                 600ps           1440
+  1101                 720ps           1560
+  1110                 840ps           1680
+  1111                 960ps           1800
+
   Optional properties:
 
     - rxc-skew-ps : Skew control of RXC pad