dt-bindings: hwmon: Add nct7802 bindings

This change documents the device tree bindings for the Nuvoton
NCT7802Y driver.

Signed-off-by: Oskar Senft <osk@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211020164213.174597-1-osk@google.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/Documentation/devicetree/bindings/hwmon/nuvoton,nct7802.yaml b/Documentation/devicetree/bindings/hwmon/nuvoton,nct7802.yaml
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@@ -0,0 +1,145 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+
+$id: http://devicetree.org/schemas/hwmon/nuvoton,nct7802.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Nuvoton NCT7802Y Hardware Monitoring IC
+
+maintainers:
+  - Guenter Roeck <linux@roeck-us.net>
+
+description: |
+  The NCT7802Y is a hardware monitor IC which supports one on-die and up to
+  5 remote temperature sensors with SMBus interface.
+
+  Datasheets:
+    https://www.nuvoton.com/export/resource-files/Nuvoton_NCT7802Y_Datasheet_V12.pdf
+
+additionalProperties: false
+
+properties:
+  compatible:
+    enum:
+      - nuvoton,nct7802
+
+  reg:
+    maxItems: 1
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 0
+
+patternProperties:
+  "^channel@[0-3]$":
+    type: object
+
+    additionalProperties: false
+
+    properties:
+      reg:
+        items:
+          - enum:
+              - 0    # Local Temperature Sensor ("LTD")
+              - 1    # Remote Temperature Sensor or Voltage Sensor 1 ("RTD1")
+              - 2    # Remote Temperature Sensor or Voltage Sensor 2 ("RTD2")
+              - 3    # Remote Temperature Sensor or Voltage Sensor 3 ("RTD3")
+
+      sensor-type:
+        items:
+          - enum:
+              - temperature
+              - voltage
+
+      temperature-mode:
+        items:
+          - enum:
+              - thermistor
+              - thermal-diode
+
+    required:
+      - reg
+
+    allOf:
+      # For channels RTD1, RTD2 and RTD3, require sensor-type to be set.
+      # Otherwise (for all other channels), do not allow temperature-mode to be
+      # set.
+      - if:
+          properties:
+            reg:
+              items:
+                - enum:
+                    - 1
+                    - 2
+                    - 3
+        then:
+          required:
+            - sensor-type
+        else:
+          not:
+            required:
+              - sensor-type
+
+      # For channels RTD1 and RTD2 and if sensor-type is "temperature", require
+      # temperature-mode to be set. Otherwise (for all other channels or
+      # sensor-type settings), do not allow temperature-mode to be set
+      - if:
+          properties:
+            reg:
+              items:
+                - enum:
+                    - 1
+                    - 2
+            sensor-type:
+              items:
+                - enum:
+                    - temperature
+        then:
+          required:
+            - temperature-mode
+        else:
+          not:
+            required:
+              - temperature-mode
+
+required:
+  - compatible
+  - reg
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        nct7802@28 {
+            compatible = "nuvoton,nct7802";
+            reg = <0x28>;
+
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            channel@0 { /* LTD */
+              reg = <0>;
+            };
+
+            channel@1 { /* RTD1 */
+              reg = <1>;
+              sensor-type = "voltage";
+            };
+
+            channel@2 { /* RTD2 */
+              reg = <2>;
+              sensor-type = "temperature";
+              temperature-mode = "thermal-diode";
+            };
+
+            channel@3 { /* RTD3 */
+              reg = <3>;
+              sensor-type = "temperature";
+            };
+        };
+    };