linux-kernel - [PATCH v2 2/8] dt-bindings: iio: dac: maxim,ds4424: add maxim,rfs-ohms property

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Message-ID: <20260127060939.3914006-3-o.rempel@pengutronix.de>
Date: Tue, 27 Jan 2026 07:09:33 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Jonathan Cameron <jic23@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
	kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org,
	Andy Shevchenko <andy@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	David Jander <david@...tonic.nl>
Subject: [PATCH v2 2/8] dt-bindings: iio: dac: maxim,ds4424: add maxim,rfs-ohms property

The Maxim DS4422/DS4424 and DS4402/DS4404 current DACs determine their
full-scale output current via external resistors (Rfs) connected to the
FSx pins. Without knowing these values, the full-scale range of the
hardware is undefined.

Add the 'maxim,rfs-ohms' property to describe these physical components.
This property is required to provide a complete description of the
hardware configuration.

Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
changes v2:
- make maxim,rfs-ohms a required property as the hardware range is undefined
  without external resistors.
- add allOf constraints to enforce 2 vs 4 items in maxim,rfs-ohms based on
  compatible string.
- drop explicit $ref for maxim,rfs-ohms to fix dt_binding_check warning.
- update example in binding to include the new required property.
---
 .../bindings/iio/dac/maxim,ds4424.yaml        | 36 +++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml b/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml
index efe63e6cb55d..400afd8771aa 100644
--- a/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml
+++ b/Documentation/devicetree/bindings/iio/dac/maxim,ds4424.yaml
@@ -27,9 +27,44 @@ properties:
 
   vcc-supply: true
 
+  maxim,rfs-ohms:
+    description: |
+      Array of resistance values in Ohms for the external Rfs resistors
+      connected to the FS pins.
+      - For DS44x2 (2 channels): 2 values required.
+      - For DS44x4 (4 channels): 4 values required.
+      Typical values range from 40000 (40 kOhm) to 160000 (160 kOhm).
+
 required:
   - compatible
   - reg
+  - maxim,rfs-ohms
+
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - maxim,ds4402
+              - maxim,ds4422
+    then:
+      properties:
+        maxim,rfs-ohms:
+          minItems: 2
+          maxItems: 2
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - maxim,ds4404
+              - maxim,ds4424
+    then:
+      properties:
+        maxim,rfs-ohms:
+          minItems: 4
+          maxItems: 4
 
 additionalProperties: false
 
@@ -43,6 +78,7 @@ examples:
             compatible = "maxim,ds4424";
             reg = <0x10>; /* When A0, A1 pins are ground */
             vcc-supply = <&vcc_3v3>;
+            maxim,rfs-ohms = <5100>, <5100>, <5100>, <5100>;
         };
     };
 ...
-- 
2.47.3