dt-bindings: iio: add backend support to sd modulator

The legacy sd modulator driver registers the sigma delta modulator as
an IIO channel provider. This implementation is not convenient when the
SD modulator has to be cascaded with another IIO device. The scaling
information is distributed across devices, which makes it difficult to
report consistent scaling data on IIO devices.

The solution is to expose these cascaded IIO devices as an aggregate
device, which report global scaling information.
Add IIO backend support to SD modulator to allow scaling information
management.

Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20240730084640.1307938-6-olivier.moysan@foss.st.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/Documentation/devicetree/bindings/iio/adc/sigma-delta-modulator.yaml b/Documentation/devicetree/bindings/iio/adc/sigma-delta-modulator.yaml
index cab0d425eaa4269bb6aed1accf4d536c9dc6373e..7d33c4e09905c4d9c695d891ecede831aca1abda 100644 (file)
--- a/Documentation/devicetree/bindings/iio/adc/sigma-delta-modulator.yaml
+++ b/Documentation/devicetree/bindings/iio/adc/sigma-delta-modulator.yaml
@@ -18,18 +18,32 @@ properties:
       - sd-modulator
       - ads1201
 
+  '#io-backend-cells':
+    const: 0
+
   '#io-channel-cells':
     const: 0
 
 required:
   - compatible
-  - '#io-channel-cells'
+
+anyOf:
+  - required: ['#io-backend-cells']
+  - required: ['#io-channel-cells']
 
 additionalProperties: false
 
 examples:
   - |
-    ads1202: adc {
+    // Backend binding example. SD modulator configured as an IIO backend device
+    ads1201_0: adc {
+      compatible = "sd-modulator";
+      #io-backend-cells = <0>;
+    };
+
+  - |
+    // Legacy binding example. SD modulator configured as an IIO channel provider
+    ads1201_1: adc {
       compatible = "sd-modulator";
       #io-channel-cells = <0>;
     };