dt-bindings: iio: adc: add docs for AD7606C-{16,18} parts

The driver will support the AD7606C-16 and AD7606C-18.
This change adds the compatible strings for these devices.

The AD7606C-16,18 channels also support these (individually configurable)
types of channels:
 - bipolar single-ended
 - unipolar single-ended
 - bipolar differential

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Alexandru Ardelean <aardelean@baylibre.com>
Link: https://patch.msgid.link/20240919130444.2100447-8-aardelean@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/adi,ad7606.yaml

@@ -14,6 +14,8 @@ description: |
   https://www.analog.com/media/en/technical-documentation/data-sheets/AD7605-4.pdf
   https://www.analog.com/media/en/technical-documentation/data-sheets/ad7606_7606-6_7606-4.pdf
   https://www.analog.com/media/en/technical-documentation/data-sheets/AD7606B.pdf
+  https://www.analog.com/media/en/technical-documentation/data-sheets/ad7606c-16.pdf
+  https://www.analog.com/media/en/technical-documentation/data-sheets/ad7606c-18.pdf
   https://www.analog.com/media/en/technical-documentation/data-sheets/AD7616.pdf
 
 properties:
@@ -24,11 +26,19 @@ properties:
       - adi,ad7606-6
       - adi,ad7606-8  # Referred to as AD7606 (without -8) in the datasheet
       - adi,ad7606b
+      - adi,ad7606c-16
+      - adi,ad7606c-18
       - adi,ad7616
 
   reg:
     maxItems: 1
 
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 0
+
   spi-cpha: true
 
   spi-cpol: true
@@ -114,6 +124,47 @@ properties:
       assumed that the pins are hardwired to VDD.
     type: boolean
 
+patternProperties:
+  "^channel@[1-8]$":
+    type: object
+    $ref: adc.yaml
+    unevaluatedProperties: false
+
+    properties:
+      reg:
+        description:
+          The channel number, as specified in the datasheet (from 1 to 8).
+        minimum: 1
+        maximum: 8
+
+      diff-channels:
+        description:
+          Each channel can be configured as a bipolar differential channel.
+          The ADC uses the same positive and negative inputs for this.
+          This property must be specified as 'reg' (or the channel number) for
+          both positive and negative inputs (i.e. diff-channels = <reg reg>).
+          Since the configuration is bipolar differential, the 'bipolar'
+          property is required.
+        items:
+          minimum: 1
+          maximum: 8
+
+      bipolar:
+        description:
+          The ADC channels can be configured as
+             * Bipolar single-ended
+             * Unipolar single-ended
+             * Bipolar differential
+          Therefore in the DT, if no channel node is specified, it is considered
+          'unipolar single-ended'. So for the other configurations the 'bipolar'
+          property must be specified. If 'diff-channels' is specified, it is
+          considered a bipolar differential channel. Otherwise it is bipolar
+          single-ended.
+
+    required:
+      - reg
+      - bipolar
+
 required:
   - compatible
   - reg
@@ -170,6 +221,25 @@ allOf:
         adi,conversion-start-gpios:
           maxItems: 1
 
+  - if:
+      not:
+        required:
+          - adi,sw-mode
+    then:
+      patternProperties:
+        "^channel@[1-8]$": false
+
+  - if:
+      not:
+        properties:
+          compatible:
+            enum:
+              - adi,ad7606c-16
+              - adi,ad7606c-18
+    then:
+      patternProperties:
+        "^channel@[1-8]$": false
+
 unevaluatedProperties: false
 
 examples:
@@ -202,4 +272,54 @@ examples:
             standby-gpios = <&gpio 24 GPIO_ACTIVE_LOW>;
         };
     };
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@0 {
+            compatible = "adi,ad7606c-18";
+            reg = <0>;
+
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            spi-max-frequency = <1000000>;
+            spi-cpol;
+            spi-cpha;
+
+            avcc-supply = <&adc_vref>;
+            vdrive-supply = <&vdd_supply>;
+
+            interrupts = <25 IRQ_TYPE_EDGE_FALLING>;
+            interrupt-parent = <&gpio>;
+
+            adi,conversion-start-gpios = <&gpio 17 GPIO_ACTIVE_HIGH>;
+            reset-gpios = <&gpio 27 GPIO_ACTIVE_HIGH>;
+            adi,first-data-gpios = <&gpio 22 GPIO_ACTIVE_HIGH>;
+            standby-gpios = <&gpio 24 GPIO_ACTIVE_LOW>;
+
+            adi,sw-mode;
+
+            channel@1 {
+                reg = <1>;
+                diff-channels = <1 1>;
+                bipolar;
+            };
+
+            channel@3 {
+                reg = <3>;
+                bipolar;
+            };
+
+            channel@8 {
+                reg = <8>;
+                diff-channels = <8 8>;
+                bipolar;
+            };
+
+        };
+    };
 ...