dt-bindings: aspeed: Add UART routing controller

Add dt-bindings for Aspeed UART routing controller.

Signed-off-by: Oskar Senft <[e-mail]>
Signed-off-by: Chia-Wei Wang <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/devicetree/bindings/mfd/aspeed-lpc.yaml

···
       - interrupts
       - snoop-ports
 
+  "^uart-routing@[0-9a-f]+$":
+    $ref: /schemas/soc/aspeed/uart-routing.yaml#
+    description: The UART routing control under LPC register space
+
 required:
   - compatible
   - reg

Documentation/devicetree/bindings/soc/aspeed/uart-routing.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+# # Copyright (c) 2018 Google LLC
+# # Copyright (c) 2021 Aspeed Technology Inc.
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/soc/aspeed/uart-routing.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Aspeed UART Routing Controller
+
+maintainers:
+  - Oskar Senft <[e-mail]>
+  - Chia-Wei Wang <[e-mail]>
+
+description:
+  The Aspeed UART routing control allow to dynamically route the inputs for
+  the built-in UARTS and physical serial I/O ports.
+
+  This allows, for example, to connect the output of UART to another UART.
+  This can be used to enable Host <-> BMC communication via UARTs, e.g. to
+  allow access to the Host's serial console.
+
+  This driver is for the BMC side. The sysfs files allow the BMC userspace
+  which owns the system configuration policy, to configure how UARTs and
+  physical serial I/O ports are routed.
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - aspeed,ast2400-uart-routing
+          - aspeed,ast2500-uart-routing
+          - aspeed,ast2600-uart-routing
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    lpc: lpc@1e789000 {
+        compatible = "aspeed,ast2600-lpc-v2", "simple-mfd", "syscon";
+        reg = <0x1e789000 0x1000>;
+
+        #address-cells = <1>;
+        #size-cells = <1>;
+        ranges = <0x0 0x1e789000 0x1000>;
+
+        uart_routing: uart-routing@98 {
+            compatible = "aspeed,ast2600-uart-routing";
+            reg = <0x98 0x8>;
+        };
+    };