dt-bindings: mmc: document mmc-slot

Document the mmc-slot, which is a subnode of a multi-slot
MMC controller, each slot is represented as a full MMC controller,
the top node handling all the shared resources and slot mux.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Message-ID: <20241128-topic-amlogic-arm32-upstream-bindings-fixes-convert-meson-mx-sdio-v4-4-11d9f9200a59@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Author: superna9999

Documentation/devicetree/bindings/mmc/mmc-slot.yaml

@@ -0,0 +1,49 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mmc/mmc-slot.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MMC slot properties
+
+maintainers:
+  - Ulf Hansson <ulf.hansson@linaro.org>
+
+description:
+  These properties defines slot properties for MMC controlers that
+  have multiple slots or ports provided by the same controller and
+  sharing the same resources.
+
+$ref: mmc-controller-common.yaml#
+
+properties:
+  $nodename:
+    pattern: "^slot(@.*)?$"
+
+  compatible:
+    const: mmc-slot
+
+  reg:
+    description:
+      the slot (or "port") ID
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    mmc {
+      #address-cells = <1>;
+      #size-cells = <0>;
+      slot@0 {
+        compatible = "mmc-slot";
+        reg = <0>;
+        bus-width = <4>;
+      };
+    };
+
+...