dt-bindings: bus: document the stm32 debug bus

Document the stm32 debug bus. The debug bus is responsible for
checking the debug sub-system accessibility before probing any related
drivers.

Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://lore.kernel.org/r/20260226-debug_bus-v6-3-5d794697798d@foss.st.com
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

Documentation/devicetree/bindings/bus/st,stm32mp131-dbg-bus.yaml

@@ -0,0 +1,76 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/bus/st,stm32mp131-dbg-bus.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: STM32 Coresight bus
+
+maintainers:
+  - Gatien Chevallier <gatien.chevallier@foss.st.com>
+
+description:
+  The STM32 debug bus is in charge of checking the debug configuration
+  of the platform before probing the peripheral drivers that rely on the debug
+  domain.
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - st,stm32mp131-dbg-bus
+          - st,stm32mp151-dbg-bus
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 1
+
+  ranges:
+    minItems: 1
+    maxItems: 2
+
+  "#access-controller-cells":
+    const: 1
+    description:
+      Contains the debug profile necessary to access the peripheral.
+
+patternProperties:
+  "@[0-9a-f]+$":
+    description: Debug related peripherals
+    type: object
+
+    additionalProperties: true
+
+    required:
+      - access-controllers
+
+required:
+  - "#access-controller-cells"
+  - "#address-cells"
+  - "#size-cells"
+  - compatible
+  - ranges
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/stm32mp1-clks.h>
+
+    dbg_bus: bus@50080000 {
+      compatible = "st,stm32mp131-dbg-bus";
+      #address-cells = <1>;
+      #size-cells = <1>;
+      #access-controller-cells = <1>;
+      ranges = <0x50080000 0x50080000 0x3f80000>;
+
+      cti@50094000 {
+        compatible = "arm,coresight-cti", "arm,primecell";
+        reg = <0x50094000 0x1000>;
+        clocks = <&rcc CK_DBG>;
+        clock-names = "apb_pclk";
+        access-controllers = <&dbg_bus 0>;
+      };
+    };