dt-bindings: iio: adc: ad4080: add AD4880 support

Add support for the AD4880, a dual-channel 20-bit 40MSPS SAR ADC
with integrated fully differential amplifiers (FDA).

The AD4880 has two independent ADC channels, each with its own SPI
configuration interface. This requires:
- Two entries in reg property for primary and secondary channel
  chip selects
- Two io-backends entries for the two data channels

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/adi,ad4080.yaml

@@ -18,7 +18,11 @@ description: |
   service a wide variety of precision, wide bandwidth data acquisition
   applications.
 
+  The AD4880 is a dual-channel variant with two independent ADC channels,
+  each with its own SPI configuration interface.
+
   https://www.analog.com/media/en/technical-documentation/data-sheets/ad4080.pdf
+  https://www.analog.com/media/en/technical-documentation/data-sheets/ad4880.pdf
 
 $ref: /schemas/spi/spi-peripheral-props.yaml#
 
@@ -34,9 +38,15 @@ properties:
       - adi,ad4086
       - adi,ad4087
       - adi,ad4088
+      - adi,ad4880
 
   reg:
-    maxItems: 1
+    minItems: 1
+    maxItems: 2
+    description:
+      SPI chip select(s). For single-channel devices, one chip select.
+      For multi-channel devices like AD4880, two chip selects are required
+      as each channel has its own SPI configuration interface.
 
   spi-max-frequency:
     description: Configuration of the SPI bus.
@@ -60,7 +70,10 @@ properties:
   vrefin-supply: true
 
   io-backends:
-    maxItems: 1
+    minItems: 1
+    items:
+      - description: Backend for channel A (primary)
+      - description: Backend for channel B (secondary)
 
   adi,lvds-cnv-enable:
     description: Enable the LVDS signal type on the CNV pin. Default is CMOS.
@@ -81,6 +94,25 @@ required:
   - vdd33-supply
   - vrefin-supply
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: adi,ad4880
+    then:
+      properties:
+        reg:
+          minItems: 2
+        io-backends:
+          minItems: 2
+    else:
+      properties:
+        reg:
+          maxItems: 1
+        io-backends:
+          maxItems: 1
+
 additionalProperties: false
 
 examples:
@@ -101,4 +133,21 @@ examples:
           io-backends = <&iio_backend>;
         };
     };
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@0 {
+          compatible = "adi,ad4880";
+          reg = <0>, <1>;
+          spi-max-frequency = <10000000>;
+          vdd33-supply = <&vdd33>;
+          vddldo-supply = <&vddldo>;
+          vrefin-supply = <&vrefin>;
+          clocks = <&cnv>;
+          clock-names = "cnv";
+          io-backends = <&iio_backend_cha>, <&iio_backend_chb>;
+        };
+    };
 ...