[PATCH v3 RFC v3] dt-bindings: iio: adc: add ad7816/7/8 digital temperature sensor / ADC

[Taha Narimani <tahanarimani3443@gmail.com>]

Document the Analog Devices AD7816, AD7817, and AD7818 digital
temperature sensor and ADC bindings in YAML format.

Please note that the driver for this device is currently in drivers/staging.
This patch is sent as an RFC to clean up and standardize the device tree
bindings prior to any major driver refactoring.

While reviewing the AD7816/7/8 datasheet to correctly document the properties,
it was noted that the current staging driver attempts to request a 'busy' GPIO
for both AD7816 and AD7817. However, the AD7816 is an 8-pin device and does
not possess a BUSY pin (only the 16-pin AD7817 has it). Therefore, in this
binding, busy-gpios is strictly limited to adi,ad7817.

This resolves the checkpatch.pl warnings regarding undocumented DT
compatible strings.

Signed-off-by: Taha Narimani <tahanarimani3443@gmail.com>
---
Changes in v3:
  - Removed redundant conditional check around gpiod_get_value() as suggested by Andy Shevchenko and Dan Carpenter.
  - Switched to dev_err_probe() to avoid deferred probe spamming.
  - Introduced local struct device *dev pointer in probe and kept the GPIO request on a single line for better readability.
  - Added the missing Fixes tag requested by Jonathan Cameron.

 .../bindings/iio/adc/adi,ad7816.yaml          | 105 ++++++++++++++++++
 1 file changed, 105 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/adi,ad7816.yaml

diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad7816.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad7816.yaml
new file mode 100644
index 0000000..48563e4
--- /dev/null
Changes in v3:
  - Removed redundant conditional check around gpiod_get_value() as suggested by Andy Shevchenko and Dan Carpenter.
  - Switched to dev_err_probe() to avoid deferred probe spamming.
  - Introduced local struct device *dev pointer in probe and kept the GPIO request on a single line for better readability.
  - Added the missing Fixes tag requested by Jonathan Cameron.

+++ b/Documentation/devicetree/bindings/iio/adc/adi,ad7816.yaml
@@ -0,0 +1,105 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/adi,ad7816.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Analog Devices AD7816/7/8 digital temperature sensor / ADC
+
+maintainers:
+  - Taha Narimani <tahanarimani3443@gmail.com>
+
+description: |
+  Analog Devices AD7816, AD7817, and AD7818 10-Bit general purpose ADC and
+  temperature sensor. The device communicates via an SPI interface.
+
+properties:
+  compatible:
+    enum:
+      - adi,ad7816
+      - adi,ad7817
+      - adi,ad7818
+
+  reg:
+    maxItems: 1
+
+  spi-max-frequency:
+    maximum: 12500000
+
+  vdd-supply:
+    description: Main power supply.
+
+  vref-supply:
+    description: |
+      Optional external reference voltage supply. If not provided, the
+      internal reference is used. Applicable for AD7816 and AD7817.
+
+  rdwr-gpios:
+    maxItems: 1
+    description: GPIO connected to the RD/WR pin.
+
+  convert-gpios:
+    maxItems: 1
+    description: GPIO connected to the CONVST (Convert Start) pin.
+
+  busy-gpios:
+    maxItems: 1
+    description: GPIO connected to the BUSY pin. Only applicable for AD7817.
+
+  interrupts:
+    maxItems: 1
+    description: OTI (Over Temperature Indicator) interrupt. Active low.
+
+required:
+  - compatible
+  - reg
+  - vdd-supply
+  - rdwr-gpios
+  - convert-gpios
+
+allOf:
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: adi,ad7817
+    then:
+      required:
+        - busy-gpios
+    else:
+      properties:
+        busy-gpios: false
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: adi,ad7818
+    then:
+      properties:
+        vref-supply: false
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@0 {
+            compatible = "adi,ad7817";
+            reg = <0>;
+            spi-max-frequency = <1000000>;
+            vdd-supply = <&vcc>;
+            vref-supply = <&vref>;
+            rdwr-gpios = <&gpio 5 GPIO_ACTIVE_HIGH>;
+            convert-gpios = <&gpio 6 GPIO_ACTIVE_HIGH>;
+            busy-gpios = <&gpio 7 GPIO_ACTIVE_HIGH>;
+            interrupts = <20 IRQ_TYPE_LEVEL_LOW>;
+            interrupt-parent = <&gpio>;
+        };
+    };
-- 
2.53.0