dt-bindings: mmc: sdhci-of-aspeed: Document Aspeed SD controller

The ASPEED SD/SDIO/MMC controller exposes two slots implementing the
SDIO Host Specification v2.00, with 1 or 4 bit data buses, or an 8 bit
data bus if only a single slot is enabled.
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/aspeed,sdhci.yaml

+# SPDX-License-Identifier: GPL-2.0-or-later
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mmc/aspeed,sdhci.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ASPEED SD/SDIO/MMC Controller
+
+maintainers:
+  - Andrew Jeffery <andrew@aj.id.au>
+  - Ryan Chen <ryanchen.aspeed@gmail.com>
+
+description: |+
+  The ASPEED SD/SDIO/eMMC controller exposes two slots implementing the SDIO
+  Host Specification v2.00, with 1 or 4 bit data buses, or an 8 bit data bus if
+  only a single slot is enabled.
+
+  The two slots are supported by a common configuration area. As the SDHCIs for
+  the slots are dependent on the common configuration area, they are described
+  as child nodes.
+
+properties:
+  compatible:
+    enum:
+      - aspeed,ast2400-sd-controller
+      - aspeed,ast2500-sd-controller
+      - aspeed,ast2600-sd-controller
+  reg:
+    maxItems: 1
+    description: Common configuration registers
+  "#address-cells":
+    const: 1
+  "#size-cells":
+    const: 1
+  ranges: true
+  clocks:
+    maxItems: 1
+    description: The SD/SDIO controller clock gate
+
+patternProperties:
+  "^sdhci@[0-9a-f]+$":
+    type: object
+    allOf:
+        - $ref: mmc-controller.yaml
+    properties:
+      compatible:
+        enum:
+          - aspeed,ast2400-sdhci
+          - aspeed,ast2500-sdhci
+          - aspeed,ast2600-sdhci
+      reg:
+        maxItems: 1
+        description: The SDHCI registers
+      clocks:
+        maxItems: 1
+        description: The SD bus clock
+      interrupts:
+        maxItems: 1
+        description: The SD interrupt shared between both slots
+      sdhci,auto-cmd12:
+        type: boolean
+        description: Specifies that controller should use auto CMD12
+    required:
+      - compatible
+      - reg
+      - clocks
+      - interrupts
+
+additionalProperties: false
+
+required:
+  - compatible
+  - reg
+  - "#address-cells"
+  - "#size-cells"
+  - ranges
+  - clocks
+
+examples:
+  - |
+    #include <dt-bindings/clock/aspeed-clock.h>
+    sdc@1e740000 {
+            compatible = "aspeed,ast2500-sd-controller";
+            reg = <0x1e740000 0x100>;
+            #address-cells = <1>;
+            #size-cells = <1>;
+            ranges = <0 0x1e740000 0x10000>;
+            clocks = <&syscon ASPEED_CLK_GATE_SDCLK>;
+
+            sdhci0: sdhci@100 {
+                    compatible = "aspeed,ast2500-sdhci";
+                    reg = <0x100 0x100>;
+                    interrupts = <26>;
+                    sdhci,auto-cmd12;
+                    clocks = <&syscon ASPEED_CLK_SDIO>;
+            };
+
+            sdhci1: sdhci@200 {
+                    compatible = "aspeed,ast2500-sdhci";
+                    reg = <0x200 0x100>;
+                    interrupts = <26>;
+                    sdhci,auto-cmd12;
+                    clocks = <&syscon ASPEED_CLK_SDIO>;
+            };
+    };