Re: [PATCH v3 1/2] dt-bindings: iio: dac: Add AD5529R

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 9 Jun 2026 16:47:23 +0200
Janani Sunil <jan.sun97@gmail.com> wrote:

> On 5/26/26 15:11, Rodrigo Alencar wrote:
> > On 26/05/19 05:42PM, Janani Sunil wrote:  
> >> Devicetree bindings for AD5529R 16 channel 12/16 bit high voltage,
> >> buffered voltage output digital-to-analog converter (DAC) with an
> >> integrated precision reference.  
> > ...
> > Probably others may comment on that, but...
> >
> > This parent node may support device addressing for multi-device support through
> > those ID pins. I suppose that each device may have its own power supplies or
> > other resources like the toggle pins or reset and enable.
> >
> > That way I suppose that an example would look like...
> >  
> >> +
> >> +patternProperties:
> >> +  "^channel@([0-9]|1[0-5])$":
> >> +    type: object
> >> +    description: Child nodes for individual channel configuration
> >> +
> >> +    properties:
> >> +      reg:
> >> +        description: Channel number.
> >> +        minimum: 0
> >> +        maximum: 15
> >> +
> >> +      adi,output-range-microvolt:
> >> +        description: |
> >> +          Output voltage range for this channel as [min, max] in microvolts.
> >> +          If not specified, defaults to 0V to 5V range.
> >> +        oneOf:
> >> +          - items:
> >> +              - const: 0
> >> +              - enum: [5000000, 10000000, 20000000, 40000000]
> >> +          - items:
> >> +              - const: -5000000
> >> +              - const: 5000000
> >> +          - items:
> >> +              - const: -10000000
> >> +              - const: 10000000
> >> +          - items:
> >> +              - const: -15000000
> >> +              - const: 15000000
> >> +          - items:
> >> +              - const: -20000000
> >> +              - const: 20000000
> >> +
> >> +    required:
> >> +      - reg
> >> +
> >> +    additionalProperties: false
> >> +
> >> +required:
> >> +  - compatible
> >> +  - reg
> >> +  - vdd-supply
> >> +  - avdd-supply
> >> +  - hvdd-supply
> >> +
> >> +dependencies:
> >> +  spi-cpha: [ spi-cpol ]
> >> +  spi-cpol: [ spi-cpha ]
> >> +
> >> +allOf:
> >> +  - $ref: /schemas/spi/spi-peripheral-props.yaml#
> >> +
> >> +unevaluatedProperties: false
> >> +
> >> +examples:
> >> +  - |
> >> +    #include <dt-bindings/gpio/gpio.h>
> >> +
> >> +    spi {
> >> +        #address-cells = <1>;
> >> +        #size-cells = <0>;
> >> +
> >> +        dac@0 {
> >> +            compatible = "adi,ad5529r-16";
> >> +            reg = <0>;
> >> +            spi-max-frequency = <25000000>;
> >> +
> >> +            vdd-supply = <&vdd_regulator>;
> >> +            avdd-supply = <&avdd_regulator>;
> >> +            hvdd-supply = <&hvdd_regulator>;
> >> +            hvss-supply = <&hvss_regulator>;
> >> +
> >> +            reset-gpios = <&gpio0 87 GPIO_ACTIVE_LOW>;
> >> +
> >> +            #address-cells = <1>;
> >> +            #size-cells = <0>;
> >> +
> >> +            channel@0 {
> >> +                reg = <0>;
> >> +                adi,output-range-microvolt = <0 5000000>;
> >> +            };
> >> +
> >> +            channel@1 {
> >> +                reg = <1>;
> >> +                adi,output-range-microvolt = <(-10000000) 10000000>;
> >> +            };
> >> +
> >> +            channel@2 {
> >> +                reg = <2>;
> >> +                adi,output-range-microvolt = <0 40000000>;
> >> +            };
> >> +        };
> >> +    };  
> > ...
> >
> > 	spi {
> > 		#address-cells = <1>;
> > 		#size-cells = <0>;
> >
> > 		multi-dac@0 {
> > 			compatible = "adi,ad5529r-16";
> > 			reg = <0>;
> > 			spi-max-frequency = <25000000>;
> >
> > 			#address-cells = <1>;
> > 			#size-cells = <0>;
> >
> > 			dac@0 {
> > 				reg = <0>;
> > 				vdd-supply = <&vdd_regulator>;
> > 				avdd-supply = <&avdd_regulator>;
> > 				hvdd-supply = <&hvdd_regulator>;
> > 				hvss-supply = <&hvss_regulator>;
> >
> > 				reset-gpios = <&gpio0 87 GPIO_ACTIVE_LOW>;
> >
> > 				#address-cells = <1>;
> > 				#size-cells = <0>;
> >
> > 				channel@0 {
> > 					reg = <0>;
> > 					adi,output-range-microvolt = <0 5000000>;
> > 				};
> >
> > 				channel@1 {
> > 					reg = <1>;
> > 					adi,output-range-microvolt = <(-10000000) 10000000>;
> > 				};
> >
> > 				channel@2 {
> > 					reg = <2>;
> > 					adi,output-range-microvolt = <0 40000000>;
> > 				};
> > 			}
> >
> > 			dac@1 {
> > 				reg = <1>;
> > 				vdd-supply = <&vdd_regulator>;
> > 				avdd-supply = <&avdd_regulator>;
> > 				hvdd-supply = <&hvdd_regulator>;
> > 				hvss-supply = <&hvss_regulator>;
> >
> > 				reset-gpios = <&gpio0 88 GPIO_ACTIVE_LOW>;
> >
> > 				#address-cells = <1>;
> > 				#size-cells = <0>;
> >
> > 				channel@0 {
> > 					reg = <0>;
> > 					adi,output-range-microvolt = <0 5000000>;
> > 				};
> >
> > 				channel@1 {
> > 					reg = <1>;
> > 					adi,output-range-microvolt = <(-10000000) 10000000>;
> > 				};
> > 			}
> > 		};
> > 	};
> >
> > then you might need something like:
> >
> > 	patternProperties:
> > 		"^dac@[0-3]$":
> >
> > and put most of the things under this node pattern.
> >
> > So the main driver that you're putting together might need to handle up to four instances.
> > Even if your current driver cannot handle this, the dt-bindings might need cover that.
> >
> > Need to double check if each dac node needs a separate compatible, so you would maybe populate
> > a platform data to be shared with the child nodes, which would be a separate driver.
> > (not sure if it would make sense to mix and match ad5529r-16 and ad5529r-12).  
> 
> Hi Rodrigo,
> 
> Thank you for looking at this.
> 
> For now, I would prefer to keep the binding scoped to a single AD5529R device instance. The current
> hardware/use case we have only needs one device node and the driver is written around that model as well.
> While the device addressing pins could allow multi-device topology, we do not have an actual platform using
> that configuration at the moment, so I would prefer not to introduce an extra parent/child binding structure
> speculatively without a validating use case.

Interesting feature - kind of similar to address control on a typical i2c bus device, or
looking at it another way a kind of distributed SPI mux.

Challenge of a binding is we need to anticipate the future.  So I think we do need something
like Rodrigo is suggesting even if we only (for now) support a single instance in the driver.
That would leave the path open to supporting the addressing at a later date.
An alternative might be to look at it like a chained device setup. In those we pretend there
is just one device with a lot of channels etc.  The snag is that here things are more loosely
coupled whereas for those devices it tends to be you have to read / write the same register
in all devices in the chain as one big SPI message.

+CC Mark Brown as he may know of some precedence for this feature. For his reference..
- Each of these device has 2 ID pins.  The SPI transfers have to contain the 2 bit
value that matches that or they are ignored.  Thus a single bus + 1 chip select can
be used to talk to 4 devices.  Question is what that looks like in device tree + I guess
longer term how to support it cleanly in SPI.

Jonathan


> 
> Best Regards,
> Janani Sunil
> 
>