dt-bindings: net: phy: Add 10-baseT1L 2.4 Vpp

Add a tristate property to advertise desired transmit level.

If the device supports the 2.4 Vpp operating mode for 10BASE-T1L,
as defined in 802.3gc, and the 2.4 Vpp transmit voltage operation
is desired, property should be set to 1. This property is used
to select whether Auto-Negotiation advertises a request to
operate the 10BASE-T1L PHY in increased transmit level mode.

If property is set to 1, the PHY shall advertise a request
to operate the 10BASE-T1L PHY in increased transmit level mode.
If property is set to zero, the PHY shall not advertise
a request to operate the 10BASE-T1L PHY in increased transmit level mode.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandru Tachici <alexandru.tachici@analog.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -77,6 +77,15 @@ properties:
     description:
       Maximum PHY supported speed in Mbits / seconds.
 
+  phy-10base-t1l-2.4vpp:
+    description: |
+      tristate, request/disable 2.4 Vpp operating mode. The values are:
+      0: Disable 2.4 Vpp operating mode.
+      1: Request 2.4 Vpp operating mode from link partner.
+      Absence of this property will leave configuration to default values.
+    $ref: "/schemas/types.yaml#/definitions/uint32"
+    enum: [0, 1]
+
   broken-turn-around:
     $ref: /schemas/types.yaml#/definitions/flag
     description: