Add dt-bindings for Aspeed UART routing controller.

Signed-off-by: Oskar Senft <redacted>
Signed-off-by: Chia-Wei Wang <redacted>
---
 .../devicetree/bindings/mfd/aspeed-lpc.yaml   |  4 ++
 .../bindings/soc/aspeed/uart-routing.yaml     | 70 +++++++++++++++++++
 2 files changed, 74 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/soc/aspeed/uart-routing.yaml

diff --git a/Documentation/devicetree/bindings/mfd/aspeed-lpc.yaml b/Documentation/devicetree/bindings/mfd/aspeed-lpc.yaml
index 54f080df5e2f..697331d840a0 100644
--- a/Documentation/devicetree/bindings/mfd/aspeed-lpc.yaml
+++ b/Documentation/devicetree/bindings/mfd/aspeed-lpc.yaml

@@ -142,6 +142,10 @@ patternProperties:
       - 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

diff --git a/Documentation/devicetree/bindings/soc/aspeed/uart-routing.yaml b/Documentation/devicetree/bindings/soc/aspeed/uart-routing.yaml
new file mode 100644
index 000000000000..534b2a9340ce
--- /dev/null
+++ b/Documentation/devicetree/bindings/soc/aspeed/uart-routing.yaml

@@ -0,0 +1,70 @@
+# 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 <osk@google.com>
+  - Chia-Wei Wang <chiawei_wang@aspeedtech.com>
+
+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.
+
+  Two types of files, uart* and io*, are presented in sysfs. The uart*
+  configures the input signal of a UART controller whereas io* configures
+  that of a physical serial port.
+
+  When read, each file shows the list of available options with currently
+  selected option marked by brackets "[]". The list of available options
+  depends on the selected file.
+
+  e.g.
+  cat /sys/bus/platform/drivers/aspeed-uart-routing/*.uart_routing/uart1
+  [io1] io2 io3 io4 uart2 uart3 uart4 io6
+
+  In this case, UART1 gets its input from IO1 (physical serial port 1).