[PATCH v2 1/2] dt-bindings: iio: adc: avia-hx711: add avia,hx710b compatible

[Piyush Patle <piyushpatle228@gmail.com>]

The HX710B shares the same two-wire interface as the HX711 but differs
in its channel and gain model: gain is fixed at 128 and the number of
trailing PD_SCK pulses selects the input channel rather than the gain.

Add avia,hx710b to the compatible enum. Document the chip differences
in the description and add chip-specific supply properties (dvdd-supply,
vsup-supply) for the HX711, a rate-gpios property for the HX711 RATE
pin, and an allOf constraint that forbids HX711-only properties on
HX710B nodes. Clarify the clock-frequency description to reflect its
actual purpose: controlling the SCK bit-bang timing. Note that AVDD
serves as the voltage reference on both chips so no separate
vref-supply is needed.

Signed-off-by: Piyush Patle <piyushpatle228@gmail.com>
---
Changes in v2:
- Remove driver implementation details (bit-banging, channel-selection
  mechanics) from the description; describe hardware behaviour only
- Drop unrelated punctuation cleanup (trailing period on PD_SCK description)
- Add dvdd-supply and vsup-supply optional properties for HX711
- Add rate-gpios optional property for the HX711 RATE pin; forbid it on
  HX710B via the allOf if/then block
- Add note to avdd-supply clarifying it serves as voltage reference on
  both chips (no separate vref-supply needed)
- Add allOf if/then block forbidding HX711-only properties on HX710B
- Fix clock-frequency description to reflect its true purpose (SCK
  bit-bang timing control, not a crystal/external clock frequency)
- Sort compatible enum alphabetically (hx710b before hx711)
- Remove redundant example comments (compatible already identifies part)
- Update HX711 example to exercise the new rate-gpios property

 .../bindings/iio/adc/avia-hx711.yaml          | 61 ++++++++++++++++---
 1 file changed, 51 insertions(+), 10 deletions(-)

diff --git a/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml b/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml
index 9c57eb13f892..35ac74a490b1 100644
--- a/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml
+++ b/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml
@@ -4,24 +4,24 @@
 $id: http://devicetree.org/schemas/iio/adc/avia-hx711.yaml#
 $schema: http://devicetree.org/meta-schemas/core.yaml#
 
-title: AVIA HX711 ADC chip for weight cells
+title: AVIA HX711 and HX710B ADCs
 
 maintainers:
   - Andreas Klinger <ak@it-klinger.de>
 
 description: |
-  Bit-banging driver using two GPIOs:
-  - sck-gpio gives a clock to the sensor with 24 cycles for data retrieval
-    and up to 3 cycles for selection of the input channel and gain for the
-    next measurement
-  - dout-gpio is the sensor data the sensor responds to the clock
+  The HX711 is a 24-bit ADC with selectable gain (32/64/128) and two
+  differential input channels. Channel A supports gain 64 and 128;
+  channel B supports gain 32.
 
-  Specifications about the driver can be found at:
-  http://www.aviaic.com/ENProducts.aspx
+  The HX710B is a 24-bit ADC with fixed gain of 128. Channel 0 is the
+  differential input and channel 1 measures the DVDD-AVDD supply
+  voltage difference.
 
 properties:
   compatible:
     enum:
+      - avia,hx710b
       - avia,hx711
 
   sck-gpios:
@@ -40,13 +40,45 @@ properties:
 
   avdd-supply:
     description:
-      Definition of the regulator used as analog supply
+      Analog supply voltage (AVDD). Also serves as the voltage reference on
+      both chips; no separate vref-supply is required.
+
+  dvdd-supply:
+    description:
+      Digital supply voltage (DVDD). HX711 only.
+
+  vsup-supply:
+    description:
+      Supply voltage for the on-chip regulator (VSUP). HX711 only.
+
+  rate-gpios:
+    description:
+      GPIO connected to the RATE pin (HX711 only). When driven low the
+      output data rate is 10 SPS; when driven high it is 80 SPS. If
+      omitted the RATE pin state is determined by the board wiring.
+    maxItems: 1
 
   clock-frequency:
+    description:
+      Controls the SCK bit-bang timing. The value is used to derive the
+      delay between SCK edges; keep the SCK high time below 60 us to
+      avoid triggering chip power-down mode. Defaults to 400 kHz if not
+      specified.
     minimum: 20000
     maximum: 2500000
     default: 400000
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          const: avia,hx710b
+    then:
+      properties:
+        vsup-supply: false
+        dvdd-supply: false
+        rate-gpios: false
+
 required:
   - compatible
   - sck-gpios
@@ -58,10 +90,19 @@ additionalProperties: false
 examples:
   - |
     #include <dt-bindings/gpio/gpio.h>
-    weight {
+    weight0 {
         compatible = "avia,hx711";
         sck-gpios = <&gpio3 10 GPIO_ACTIVE_HIGH>;
         dout-gpios = <&gpio0 7 GPIO_ACTIVE_HIGH>;
+        rate-gpios = <&gpio0 9 GPIO_ACTIVE_HIGH>;
         avdd-supply = <&avdd>;
         clock-frequency = <100000>;
     };
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    weight1 {
+        compatible = "avia,hx710b";
+        sck-gpios = <&gpio3 11 GPIO_ACTIVE_HIGH>;
+        dout-gpios = <&gpio0 8 GPIO_ACTIVE_HIGH>;
+        avdd-supply = <&avdd>;
+    };
-- 
2.43.0