dt-bindings: iio: adc: ad7606: Add iio backend bindings

Add the required properties for iio-backend support, as well as an
example and the conditions to mutually exclude interruption and
conversion trigger with iio-backend.
The iio-backend's function is to controls the communication, and thus the
interruption pin won't be available anymore.
As a consequence, the conversion pin must be controlled externally since
we will miss information about when every single conversion cycle (i.e
conversion + data transfer) ends, hence a PWM is introduced to trigger
the conversions.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Guillaume Stols <gstols@baylibre.com>
Link: https://patch.msgid.link/20241015-ad7606_add_iio_backend_support-v5-2-654faf1ae08c@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

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

@@ -129,6 +129,29 @@ properties:
       assumed that the pins are hardwired to VDD.
     type: boolean
 
+  pwms:
+    description:
+      In case the conversion is triggered by a PWM instead of a GPIO plugged to
+      the CONVST pin, the PWM must be referenced.
+      The first is the PWM connected to CONVST or CONVST1 for the chips with the
+      2nd PWM connected to CONVST2, if CONVST2 is available and not shorted to
+      CONVST1.
+    minItems: 1
+    maxItems: 2
+
+  pwm-names:
+    items:
+      - const: convst1
+      - const: convst2
+
+  io-backends:
+    description:
+      A reference to the iio-backend, which is responsible handling the BUSY
+      pin's falling edge and communication.
+      An example of backend can be found at
+      http://analogdevicesinc.github.io/hdl/library/axi_ad7606x/index.html
+
+
 patternProperties:
   "^channel@[1-8]$":
     type: object
@@ -175,12 +198,22 @@ required:
   - reg
   - avcc-supply
   - vdrive-supply
-  - interrupts
-  - adi,conversion-start-gpios
 
 allOf:
   - $ref: /schemas/spi/spi-peripheral-props.yaml#
 
+  - oneOf:
+      - required:
+          - adi,conversion-start-gpios
+      - required:
+          - pwms
+
+  - oneOf:
+      - required:
+          - interrupts
+      - required:
+          - io-backends
+
   - if:
       properties:
         compatible:
@@ -222,6 +255,10 @@ allOf:
         adi,sw-mode: false
     else:
       properties:
+        pwms:
+          maxItems: 1
+        pwm-names:
+          maxItems: 1
         adi,conversion-start-gpios:
           maxItems: 1
 
@@ -247,6 +284,29 @@ allOf:
 unevaluatedProperties: false
 
 examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    iio-backend {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        adi_adc@0 {
+            compatible = "adi,ad7606b";
+            reg = <0>;
+            pwms = <&axi_pwm_gen 0 0>;
+
+            avcc-supply = <&adc_vref>;
+            vdrive-supply = <&vdd_supply>;
+
+            reset-gpios = <&gpio0 91 GPIO_ACTIVE_HIGH>;
+            standby-gpios = <&gpio0 90 GPIO_ACTIVE_LOW>;
+            adi,range-gpios = <&gpio0 89 GPIO_ACTIVE_HIGH>;
+            adi,oversampling-ratio-gpios = <&gpio0 88 GPIO_ACTIVE_HIGH
+                                            &gpio0 87 GPIO_ACTIVE_HIGH
+                                            &gpio0 86 GPIO_ACTIVE_HIGH>;
+            io-backends = <&iio_backend>;
+        };
+    };
+
   - |
     #include <dt-bindings/gpio/gpio.h>
     #include <dt-bindings/interrupt-controller/irq.h>