[PATCH v4 1/7] 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, vref-supply) and a rate-gpios property for the HX711 RATE
pin. Add allOf constraints that forbid HX711-only properties on HX710B
nodes and vice versa. Clarify the clock-frequency description to
reflect its actual purpose: controlling the SCK bit-bang timing.

Signed-off-by: Piyush Patle <piyushpatle228@gmail.com>
---
Changes in v4:
- Add vref-supply for the HX710B VREF reference voltage pin.
- Remove dvdd-supply from the HX710B forbidden properties list; the
  HX710B has a DVDD supply and the DVDD-AVDD channel relies on it.
- Add allOf block forbidding vref-supply on HX711 nodes.
- Add an HX710B example showing vref-supply.
- Update description: avoid specific channel-number references in
  hardware text.

Changes in v3:
- Drop the vref-supply mention from avdd-supply; no such binding
  property exists.
- Drop the clock-frequency sentence that repeated the schema default.
- Restore the example node name to weight.
- Remove the separate HX710B example.

Changes in v2:
- Remove driver implementation details from the description and describe
  hardware behaviour only.
- Drop unrelated punctuation cleanup.
- Add dvdd-supply and vsup-supply optional properties for HX711.
- Add rate-gpios optional property for the HX711 RATE pin and forbid it
  on HX710B.
- Add the allOf if/then block forbidding HX711-only properties on
  HX710B nodes.
- Clarify clock-frequency as SCK bit-bang timing, not a crystal or
  external clock input.
- Sort compatible enum alphabetically.
- Remove redundant example comments.
- Update the HX711 example to exercise rate-gpios.
---
 .../bindings/iio/adc/avia-hx711.yaml          | 82 +++++++++++++++----
 1 file changed, 67 insertions(+), 15 deletions(-)

diff --git a/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml b/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml
index 9c57eb13f892..fddd296bfaca 100644
--- a/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml
+++ b/Documentation/devicetree/bindings/iio/adc/avia-hx711.yaml
@@ -4,49 +4,91 @@
 $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. One input measures
+  the differential voltage between the two input pins; a second measures
+  the DVDD-AVDD supply voltage difference for battery level detection.
 
 properties:
   compatible:
     enum:
+      - avia,hx710b
       - avia,hx711
 
   sck-gpios:
     description:
-      Definition of the GPIO for the clock (output). In the datasheet it is
-      named PD_SCK
+      GPIO for the clock output (PD_SCK in the datasheet).
     maxItems: 1
 
   dout-gpios:
     description:
-      Definition of the GPIO for the data-out sent by the sensor in
-      response to the clock (input).
-      See Documentation/devicetree/bindings/gpio/gpio.txt for information
-      on how to specify a consumer gpio.
+      GPIO for the data output from the sensor (DOUT in the datasheet).
     maxItems: 1
 
   avdd-supply:
     description:
-      Definition of the regulator used as analog supply
+      Analog supply voltage (AVDD). Also serves as the voltage reference on
+      both chips.
+
+  dvdd-supply:
+    description:
+      Digital supply voltage (DVDD). For the HX710B, DVDD must be greater
+      than or equal to AVDD. When DVDD is a battery rail and AVDD is a
+      regulated supply, one channel monitors the DVDD-AVDD difference for
+      battery level detection.
+
+  vsup-supply:
+    description:
+      Supply voltage for the on-chip regulator (VSUP). HX711 only.
+
+  vref-supply:
+    description:
+      Reference voltage input (VREF). HX710B only. When omitted, the driver
+      assumes VREF is tied to AVDD on the board.
+
+  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.
     minimum: 20000
     maximum: 2500000
     default: 400000
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          const: avia,hx710b
+    then:
+      properties:
+        vsup-supply: false
+        rate-gpios: false
+
+  - if:
+      properties:
+        compatible:
+          const: avia,hx711
+    then:
+      properties:
+        vref-supply: false
+
 required:
   - compatible
   - sck-gpios
@@ -62,6 +104,16 @@ examples:
         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>
+    weight {
+        compatible = "avia,hx710b";
+        sck-gpios = <&gpio3 10 GPIO_ACTIVE_HIGH>;
+        dout-gpios = <&gpio0 7 GPIO_ACTIVE_HIGH>;
+        avdd-supply = <&avdd>;
+        vref-supply = <&vref>;
+    };
-- 
2.43.0