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).
+
 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

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

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

> +          minItems: 2

Remove this...

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


> +          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

>  
>  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
> 

On Tue, Jan 27, 2026 at 07:49:20PM +0000, Conor Dooley wrote:
> On Tue, Jan 27, 2026 at 07:09:33AM +0100, Oleksij Rempel wrote:
> > 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?

> > +
> >  required:
> >    - compatible
> >    - reg
> > +  - maxim,rfs-ohms
> > +
> > +allOf:
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            enum:
> > +              - maxim,ds4402
> > +              - maxim,ds4422
> > +    then:
> > +      properties:
> > +        maxim,rfs-ohms:
> 
> > +          minItems: 2
> 
> Remove this...
> 
> > +          maxItems: 2
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            enum:
> > +              - maxim,ds4404
> > +              - maxim,ds4424
> > +    then:
> > +      properties:
> > +        maxim,rfs-ohms:
> > +          minItems: 4
> 
> 
> > +          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
> 
> >  
> >  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
> > 

On Tue, 27 Jan 2026 19:55:26 +0000
Conor Dooley <conor@kernel.org> wrote:

> On Tue, Jan 27, 2026 at 07:49:20PM +0000, Conor Dooley wrote:
> > On Tue, Jan 27, 2026 at 07:09:33AM +0100, Oleksij Rempel wrote:  
> > > 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.

> > > +
> > >  required:
> > >    - compatible
> > >    - reg
> > > +  - maxim,rfs-ohms
> > > +
> > > +allOf:
> > > +  - if:
> > > +      properties:
> > > +        compatible:
> > > +          contains:
> > > +            enum:
> > > +              - maxim,ds4402
> > > +              - maxim,ds4422
> > > +    then:
> > > +      properties:
> > > +        maxim,rfs-ohms:  
> >   
> > > +          minItems: 2  
> > 
> > Remove this...
> >   
> > > +          maxItems: 2
> > > +  - if:
> > > +      properties:
> > > +        compatible:
> > > +          contains:
> > > +            enum:
> > > +              - maxim,ds4404
> > > +              - maxim,ds4424
> > > +    then:
> > > +      properties:
> > > +        maxim,rfs-ohms:
> > > +          minItems: 4  
> > 
> >   
> > > +          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
> >   
> > >  
> > >  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

On Wed, Jan 28, 2026 at 09:01:18AM +0100, David Jander wrote:
> On Tue, 27 Jan 2026 19:55:26 +0000
> Conor Dooley <conor@kernel.org> wrote:
> 
> > On Tue, Jan 27, 2026 at 07:49:20PM +0000, Conor Dooley wrote:
> > > On Tue, Jan 27, 2026 at 07:09:33AM +0100, Oleksij Rempel wrote:  
> > > > 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:

No no, don't apologise - that's good info and makes sense. Thanks.

> 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.