On Tue, 27 Jan 2026 19:55:26 +0000
Conor Dooley [off-list ref] wrote:

On Tue, Jan 27, 2026 at 07:49:20PM +0000, Conor Dooley wrote:

quoted

On Tue, Jan 27, 2026 at 07:09:33AM +0100, Oleksij Rempel wrote:  

quoted

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@pengutronix.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).  

Add here
maxItems: 4
minItems: 2

Are 40kOhm and 160kOhm actual max/min values, or just a suggested range?  

Datasheet for the ds4424 seems to imply they're actual max/min values:
"Input resistors (RFS) must be between the speciifed values to ensure the
device meets its accuracy and linearity specifications."
In that case, consider also adding something like:
    items:
      maximum: 40000
      minimum: 160000

Although, that would complain about the 5100 Ohms you're using. How come
the example lies outside of the "typical" range?

Sorry to chime in here out of nowhere with this, but 2 things:
1. Rfs for DS4402/4 has a different "typical" range than DS4424 (different
Vref and different output current range).
2. "Typical" or "recommended" ranges should not translate to a hard limit in
the driver. IMHO, no max or min value should be enforced here.

quoted

quoted

+
 required:
   - compatible
   - reg
+  - maxim,rfs-ohms
+
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - maxim,ds4402
+              - maxim,ds4422
+    then:
+      properties:
+        maxim,rfs-ohms:  

quoted

+          minItems: 2  

Remove this...
  

quoted

+          maxItems: 2
+  - if:
+      properties:
+        compatible:
+          contains:
+            enum:
+              - maxim,ds4404
+              - maxim,ds4424
+    then:
+      properties:
+        maxim,rfs-ohms:
+          minItems: 4  

quoted

+          maxItems: 4  

...and this. The outer-most constraints should be in the definition and
the if/else bit just adjusts whichever bounds it needs to.

Cheers,
Conor.

pw-bot: changes-requested
  

quoted

 
 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
  

-- 
David Jander