dt-bindings: power: supply: Add Richtek RT9471 battery charger

Add bindings for the Richtek RT9471 I2C controlled battery charger.
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Co-developed-by: Alina Yu <alina_yu@richtek.com>
Signed-off-by: Alina Yu <alina_yu@richtek.com>
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Documentation/devicetree/bindings/power/supply/richtek,rt9471.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/power/supply/richtek,rt9471.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Richtek RT9471 3A Single Cell Switching Battery charger
+
+maintainers:
+  - Alina Yu <alina_yu@richtek.com>
+  - ChiYuan Huang <cy_huang@richtek.com>
+
+description: |
+  RT9471 is a switch-mode single cell Li-Ion/Li-Polymer battery charger for
+  portable applications. It supports USB BC1.2 port detection, current and
+  voltage regulations in both charging and boost mode.
+
+  Datasheet is available at
+  https://www.richtek.com/assets/product_file/RT9471=RT9471D/DS9471D-02.pdf
+
+properties:
+  compatible:
+    const: richtek,rt9471
+
+  reg:
+    maxItems: 1
+
+  charge-enable-gpios:
+    description: GPIO used to turn on and off charging.
+    maxItems: 1
+
+  wakeup-source: true
+
+  interrupts:
+    maxItems: 1
+
+  usb-otg-vbus-regulator:
+    type: object
+    $ref: /schemas/regulator/regulator.yaml#
+    unevaluatedProperties: false
+
+required:
+  - compatible
+  - reg
+  - wakeup-source
+  - interrupts
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    #include <dt-bindings/gpio/gpio.h>
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      charger@53 {
+        compatible = "richtek,rt9471";
+        reg = <0x53>;
+        charge-enable-gpios = <&gpio26 1 GPIO_ACTIVE_LOW>;
+        wakeup-source;
+        interrupts-extended = <&gpio_intc 32 IRQ_TYPE_EDGE_FALLING>;
+
+        usb-otg-vbus-regulator {
+          regulator-name = "usb-otg-vbus";
+          regulator-min-microvolt = <4850000>;
+          regulator-max-microvolt = <5300000>;
+          regulator-min-microamp = <500000>;
+          regulator-max-microamp = <1200000>;
+        };
+      };
+    };