dt-bindings: gpio: Binding for Realtek Otto GPIO

Add a binding description for Realtek's GPIO controller found on several
of their MIPS-based SoCs (codenamed Otto), such as the RTL838x and
RTL839x series of switch SoCs.

A fallback binding 'realtek,otto-gpio' is provided for cases where the
actual port ordering is not known yet, and enabling the interrupt
controller may result in uncaught interrupts.
Signed-off-by: Sander Vanheule <sander@svanheule.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Documentation/devicetree/bindings/gpio/realtek,otto-gpio.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/gpio/realtek,otto-gpio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Realtek Otto GPIO controller
+
+maintainers:
+  - Sander Vanheule <sander@svanheule.net>
+  - Bert Vermeulen <bert@biot.com>
+
+description: |
+  Realtek's GPIO controller on their MIPS switch SoCs (Otto platform) consists
+  of two banks of 32 GPIOs. These GPIOs can generate edge-triggered interrupts.
+  Each bank's interrupts are cascased into one interrupt line on the parent
+  interrupt controller, if provided.
+  This binding allows defining a single bank in the devicetree. The interrupt
+  controller is not supported on the fallback compatible name, which only
+  allows for GPIO port use.
+
+properties:
+  $nodename:
+    pattern: "^gpio@[0-9a-f]+$"
+
+  compatible:
+    items:
+      - enum:
+          - realtek,rtl8380-gpio
+          - realtek,rtl8390-gpio
+      - const: realtek,otto-gpio
+
+  reg:
+    maxItems: 1
+
+  "#gpio-cells":
+    const: 2
+
+  gpio-controller: true
+
+  ngpios:
+    minimum: 1
+    maximum: 32
+
+  interrupt-controller: true
+
+  "#interrupt-cells":
+    const: 2
+
+  interrupts:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - "#gpio-cells"
+  - gpio-controller
+
+additionalProperties: false
+
+dependencies:
+  interrupt-controller: [ interrupts ]
+
+examples:
+  - |
+      gpio@3500 {
+        compatible = "realtek,rtl8380-gpio", "realtek,otto-gpio";
+        reg = <0x3500 0x1c>;
+        gpio-controller;
+        #gpio-cells = <2>;
+        ngpios = <24>;
+        interrupt-controller;
+        #interrupt-cells = <2>;
+        interrupt-parent = <&rtlintc>;
+        interrupts = <23>;
+      };
+
+...