dt-bindings: fpga: document Lattice sysCONFIG FPGA manager

Add Device Tree Binding doc for configuring Lattice ECP5 FPGA over
Slave SPI sysCONFIG interface.

Signed-off-by: Ivan Bornyakov <i.bornyakov@metrotek.ru>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Xu Yilun <yilun.xu@intel.com>
Link: https://lore.kernel.org/r/20221025053947.2737-3-i.bornyakov@metrotek.ru
Signed-off-by: Xu Yilun <yilun.xu@intel.com>

Documentation/devicetree/bindings/fpga/lattice,sysconfig.yaml

@@ -0,0 +1,81 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/fpga/lattice,sysconfig.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Lattice Slave SPI sysCONFIG FPGA manager
+
+maintainers:
+  - Ivan Bornyakov <i.bornyakov@metrotek.ru>
+
+description: |
+  Lattice sysCONFIG port, which is used for FPGA configuration, among others,
+  have Slave Serial Peripheral Interface. Only full reconfiguration is
+  supported.
+
+  Programming of ECP5 is done by writing uncompressed bitstream image in .bit
+  format into FPGA's SRAM configuration memory.
+
+properties:
+  compatible:
+    enum:
+      - lattice,sysconfig-ecp5
+
+  reg:
+    maxItems: 1
+
+  program-gpios:
+    description:
+      A GPIO line connected to PROGRAMN (active low) pin of the device.
+      Initiates configuration sequence.
+    maxItems: 1
+
+  init-gpios:
+    description:
+      A GPIO line connected to INITN (active low) pin of the device.
+      Indicates that the FPGA is ready to be configured.
+    maxItems: 1
+
+  done-gpios:
+    description:
+      A GPIO line connected to DONE (active high) pin of the device.
+      Indicates that the configuration sequence is complete.
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+
+allOf:
+  - $ref: /schemas/spi/spi-peripheral-props.yaml
+
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: lattice,sysconfig-ecp5
+    then:
+      properties:
+        spi-max-frequency:
+          maximum: 60000000
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        fpga-mgr@0 {
+            compatible = "lattice,sysconfig-ecp5";
+            reg = <0>;
+            spi-max-frequency = <20000000>;
+            program-gpios = <&gpio3 4 GPIO_ACTIVE_LOW>;
+            init-gpios = <&gpio3 3 GPIO_ACTIVE_LOW>;
+            done-gpios = <&gpio3 2 GPIO_ACTIVE_HIGH>;
+        };
+    };