...

quoted

+    then:
+      properties:
+        io-backends:
+          minItems: 2
+      required:
+        - adi,aux-spi-cs
+    else:
+      properties:
+        io-backends:
+          maxItems: 1
+
 additionalProperties: false

 examples:

@@ -98,4 +127,22 @@ examples:
           io-backends = <&iio_backend>;
         };
     };
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@0 {
+          compatible = "adi,ad4880";
+          reg = <0>;
+          adi,aux-spi-cs = <1>;

We can already have multiple reg for a multiple CS device.

             reg = <0>, <1>;

So we shouldn't need a new adi,aux-spi-cs property for that.

Sure, that was the initial plan but for some reason going for multiple regs gets me to this:

[   11.396833]  spi_new_ancillary_device from ad4080_probe+0x4b8/0x5a4
[   11.396861]  ad4080_probe from really_probe+0xc8/0x2c8
[   11.397281] ad4080 spi1.0: chipselect 1 already in use
[   11.397297] ad4080 spi1.0: failed to register ancillary device
[   11.397317] ad4080 spi1.0: probe with driver ad4080 failed with error -16

While the aux-spi-cs works fine. Any tips?

quoted

+          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>;
+        };
+    };
 ...