spi: dt-bindings: add binding doc for spi-mtk-snfi

Add device-tree binding documentation for Mediatek SPI-NAND Flash
Interface.
Signed-off-by: NChuanhong Guo <gch981213@gmail.com>
Reviewed-by: NKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220424032527.673605-5-gch981213@gmail.comSigned-off-by: NMark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/mediatek,spi-mtk-snfi.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/spi/mediatek,spi-mtk-snfi.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: SPI-NAND flash controller for MediaTek ARM SoCs
+
+maintainers:
+  - Chuanhong Guo <gch981213@gmail.com>
+
+description: |
+  The Mediatek SPI-NAND flash controller is an extended version of
+  the Mediatek NAND flash controller. It can perform standard SPI
+  instructions with one continuous write and one read for up-to 0xa0
+  bytes. It also supports typical SPI-NAND page cache operations
+  in single, dual or quad IO mode with pipelined ECC encoding/decoding
+  using the accompanying ECC engine. There should be only one spi
+  slave device following generic spi bindings.
+
+allOf:
+  - $ref: /schemas/spi/spi-controller.yaml#
+
+properties:
+  compatible:
+    enum:
+      - mediatek,mt7622-snand
+      - mediatek,mt7629-snand
+
+  reg:
+    items:
+      - description: core registers
+
+  interrupts:
+    items:
+      - description: NFI interrupt
+
+  clocks:
+    items:
+      - description: clock used for the controller
+      - description: clock used for the SPI bus
+
+  clock-names:
+    items:
+      - const: nfi_clk
+      - const: pad_clk
+
+  nand-ecc-engine:
+    description: device-tree node of the accompanying ECC engine.
+    $ref: /schemas/types.yaml#/definitions/phandle
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - clocks
+  - clock-names
+  - nand-ecc-engine
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    #include <dt-bindings/clock/mt7622-clk.h>
+    soc {
+      #address-cells = <2>;
+      #size-cells = <2>;
+      snfi: spi@1100d000 {
+        compatible = "mediatek,mt7622-snand";
+        reg = <0 0x1100d000 0 0x1000>;
+        interrupts = <GIC_SPI 96 IRQ_TYPE_LEVEL_LOW>;
+        clocks = <&pericfg CLK_PERI_NFI_PD>, <&pericfg CLK_PERI_SNFI_PD>;
+        clock-names = "nfi_clk", "pad_clk";
+        nand-ecc-engine = <&bch>;
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        flash@0 {
+          compatible = "spi-nand";
+          reg = <0>;
+          spi-tx-bus-width = <4>;
+          spi-rx-bus-width = <4>;
+          nand-ecc-engine = <&snfi>;
+        };
+      };
+    };