linux-kernel - [PATCH net-next v2 1/3] dt-bindings: net: ethernet-phy: add property mac-termination-ohms

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Message-Id: <20250408-dp83822-mac-impedance-v2-1-fefeba4a9804@liebherr.com>
Date: Tue, 08 Apr 2025 09:45:32 +0200
From: Dimitri Fedrau via B4 Relay <devnull+dimitri.fedrau.liebherr.com@...nel.org>
To: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>, 
 Russell King <linux@...linux.org.uk>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, Florian Fainelli <f.fainelli@...il.com>
Cc: netdev@...r.kernel.org, devicetree@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Dimitri Fedrau <dimitri.fedrau@...bherr.com>, 
 Dimitri Fedrau <dima.fedrau@...il.com>
Subject: [PATCH net-next v2 1/3] dt-bindings: net: ethernet-phy: add
 property mac-termination-ohms

From: Dimitri Fedrau <dimitri.fedrau@...bherr.com>

Add property mac-termination-ohms in the device tree bindings for selecting
the resistance value of the builtin series termination resistors of the
PHY. Changing the resistance to an appropriate value can reduce signal
reflections and therefore improve signal quality.

Signed-off-by: Dimitri Fedrau <dimitri.fedrau@...bherr.com>
---
 Documentation/devicetree/bindings/net/ethernet-phy.yaml | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/Documentation/devicetree/bindings/net/ethernet-phy.yaml b/Documentation/devicetree/bindings/net/ethernet-phy.yaml
index 824bbe4333b7ed95cc39737d3c334a20aa890f01..93574c2726e5b2bc81a2dfb2462eb73c7cbfe6a8 100644
--- a/Documentation/devicetree/bindings/net/ethernet-phy.yaml
+++ b/Documentation/devicetree/bindings/net/ethernet-phy.yaml
@@ -238,6 +238,15 @@ properties:
       peak-to-peak specified in ANSI X3.263. When omitted, the PHYs default
       will be left as is.

+  mac-termination-ohms:
+    description:
+      The xMII signals need series termination on the driver side to match both
+      the output driver impedance and the line characteristic impedance, to
+      prevent reflections and EMI problems. Select a resistance value which is
+      supported by the builtin resistors of the PHY, otherwise the resistors may
+      have to be placed on board. When omitted, the PHYs default will be left as
+      is.
+
   leds:
     type: object

-- 
2.39.5