spi: cadence: add dt-bindings documentation for Cadence XSPI controller

Add DT binding for Cadence's XSPI controller driver.
Signed-off-by: Konrad Kociolek <konrad@cadence.com>
Signed-off-by: Jayshri Pawar <jpawar@cadence.com>
Signed-off-by: Parshuram Thombare <pthombar@cadence.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1632038705-23805-1-git-send-email-pthombar@cadence.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/cdns,xspi.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+# Copyright 2020-21 Cadence
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/spi/cdns,xspi.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Cadence XSPI Controller
+
+maintainers:
+  - Parshuram Thombare <pthombar@cadence.com>
+
+description: |
+  The XSPI controller allows SPI protocol communication in
+  single, dual, quad or octal wire transmission modes for
+  read/write access to slaves such as SPI-NOR flash.
+
+allOf:
+  - $ref: "spi-controller.yaml#"
+
+properties:
+  compatible:
+    const: cdns,xspi-nor
+
+  reg:
+    items:
+      - description: address and length of the controller register set
+      - description: address and length of the Slave DMA data port
+      - description: address and length of the auxiliary registers
+
+  reg-names:
+    items:
+      - const: io
+      - const: sdma
+      - const: aux
+
+  interrupts:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - interrupts
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    bus {
+        #address-cells = <2>;
+        #size-cells = <2>;
+
+        xspi: spi@a0010000 {
+            #address-cells = <1>;
+            #size-cells = <0>;
+            compatible = "cdns,xspi-nor";
+            reg = <0x0 0xa0010000 0x0 0x1040>,
+                  <0x0 0xb0000000 0x0 0x1000>,
+                  <0x0 0xa0020000 0x0 0x100>;
+            reg-names = "io", "sdma", "aux";
+            interrupts = <0 90 IRQ_TYPE_LEVEL_HIGH>;
+            interrupt-parent = <&gic>;
+
+            flash@0 {
+                compatible = "jedec,spi-nor";
+                spi-max-frequency = <75000000>;
+                reg = <0>;
+            };
+
+            flash@1 {
+                compatible = "jedec,spi-nor";
+                spi-max-frequency = <75000000>;
+                reg = <1>;
+            };
+        };
+    };