dt-bindings: net: ethernet-phy: add property tx-amplitude-100base-tx-…

…percent

Add property tx-amplitude-100base-tx-percent in the device tree bindings
for configuring the tx amplitude of 100BASE-TX PHYs. Modifying it can be
necessary to compensate losses on the PCB and connector, so the voltages
measured on the RJ45 pins are conforming.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Dimitri Fedrau <dimitri.fedrau@liebherr.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250214-dp83822-tx-swing-v5-1-02ca72620599@liebherr.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/ethernet-phy.yaml

@@ -232,6 +232,12 @@ properties:
       PHY's that have configurable TX internal delays. If this property is
       present then the PHY applies the TX delay.
 
+  tx-amplitude-100base-tx-percent:
+    description:
+      Transmit amplitude gain applied for 100BASE-TX. 100% matches 2V
+      peak-to-peak specified in ANSI X3.263. When omitted, the PHYs default
+      will be left as is.
+
   leds:
     type: object