net: phy: micrel: Use correct skew values on KSZ9021
Commit ff7bd212cb8a ("net: phy: micrel: fix divisor value for KSZ9031
phy skew") fixed the skew value divisor for the KSZ9031, but left the
code using the same divisor for the KSZ9021, which is incorrect.
The preceding commit c16e69f702b1 ("net: phy: micrel: add documentation
for Micrel KSZ90x1 binding") added the DTS documentation for the
KSZ90x1, changing it from the equivalent file in the Linux kernel to
correctly state that for this part the skew value is set in 120ps steps,
whereas the Linux documentation and driver continue to this day to use
the incorrect value of 200 that came from the original KSZ9021 datasheet
before it was corrected in revision 1.2 (Feb 2014).
This commit sorts out the resulting confusion in a consistent way by
making the following changes:
- Update the documentation to be clear about what the skew values mean,
in the same was as for the KSZ9031.
- Update the Micrel PHY driver to select the appropriate divisor for
both parts.
- Adjust all the device trees that state skew values for KSZ9021 PHYs to
use values based on 120ps steps instead of 200ps steps. This will result
in the same values being programmed into the skew registers as the
equivalent device trees in the Linux kernel do, where it incorrectly
uses 200ps steps (since that's where all these device trees were copied
from).
Signed-off-by: James Byrne <james.byrne@origamienergy.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/doc/device-tree-bindings/net/micrel-ksz90x1.txt b/doc/device-tree-bindings/net/micrel-ksz90x1.txt
index 307f53f..a214d35 100644
--- a/doc/device-tree-bindings/net/micrel-ksz90x1.txt
+++ b/doc/device-tree-bindings/net/micrel-ksz90x1.txt
@@ -14,6 +14,33 @@
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