dt-bindings: misc: lwn,bk4-spi: Add binding

Add a lwn,bk4-spi.yaml binding for Liebherr's BK4 external SPI controller.

Currently, the compatible string used for this device is "lwn,bk4",
which is the same as the board compatible string documented at fsl.yaml.

This causes several dt-schema warnings:

make dtbs_check DT_SCHEMA_FILES=fsl.yaml
...

['lwn,bk4'] is too short
'lwn,bk4' is not one of ['tq,imx8dxp-tqma8xdp-mba8xx']
'lwn,bk4' is not one of ['tq,imx8qxp-tqma8xqp-mba8xx']
'lwn,bk4' is not one of ['armadeus,imx1-apf9328', 'fsl,imx1ads']
...

Use a more specific "lwn,bk4-spi" compatible string for this
device.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Link: https://patch.msgid.link/20241023120015.1049008-1-festevam@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/misc/lwn,bk4-spi.yaml

@@ -0,0 +1,54 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/misc/lwn,bk4-spi.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Liebherr's BK4 external SPI controller
+
+maintainers:
+  - Lukasz Majewski <lukma@denx.de>
+
+description: |
+  Liebherr's BK4 external SPI controller is a device which handles data
+  acquisition from compatible industrial peripherals.
+  The SPI is used for data and management purposes in both master and
+  slave modes.
+
+allOf:
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+
+properties:
+  compatible:
+    const: lwn,bk4-spi
+
+  reg:
+    maxItems: 1
+
+  spi-max-frequency:
+    maximum: 30000000
+
+  fsl,spi-cs-sck-delay: true
+
+  fsl,spi-sck-cs-delay: true
+
+required:
+  - compatible
+  - spi-max-frequency
+
+additionalProperties: false
+
+examples:
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        spidev@0 {
+            compatible = "lwn,bk4-spi";
+            reg = <0>;
+            spi-max-frequency = <30000000>;
+            fsl,spi-cs-sck-delay = <200>;
+            fsl,spi-sck-cs-delay = <400>;
+        };
+    };

Documentation/devicetree/bindings/misc/lwn-bk4.txt

@@ -1,26 +0,0 @@
-* Liebherr's BK4 controller external SPI
-
-A device which handles data acquisition from compatible industrial
-peripherals.
-The SPI is used for data and management purposes in both master and
-slave modes.
-
-Required properties:
-
-- compatible : Should be "lwn,bk4"
-
-Required SPI properties:
-
-- reg : Should be address of the device chip select within
-  the controller.
-
-- spi-max-frequency : Maximum SPI clocking speed of device in Hz, should be
-  30MHz at most for the Liebherr's BK4 external bus.
-
-Example:
-
-spidev0: spi@0 {
-	compatible = "lwn,bk4";
-	spi-max-frequency = <30000000>;
-	reg = <0>;
-};