Add bindings for the NI 16550 UART.

Signed-off-by: Brenda Streiff <brenda.streiff@ni.com>
Cc: Gratian Crisan <gratian.crisan@ni.com>
Cc: Jason Smith <jason.smith@ni.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
---
 .../bindings/serial/ni,ni16550.yaml           | 51 +++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/serial/ni,ni16550.yaml

diff --git a/Documentation/devicetree/bindings/serial/ni,ni16550.yaml b/Documentation/devicetree/bindings/serial/ni,ni16550.yaml
new file mode 100644
index 000000000000..72ab125dd892
--- /dev/null
+++ b/Documentation/devicetree/bindings/serial/ni,ni16550.yaml
@@ -0,0 +1,51 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/serial/ni,ni16550.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: NI 16550 asynchronous serial interface (UART)
+
+maintainers:
+  - Brenda Streiff <brenda.streiff@ni.com>
+
+allOf:
+  - $ref: serial.yaml#
+
+properties:
+  compatible:
+    const: ni,ni16550
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  ni,serial-port-mode:
+    description: Indicates whether this is an RS-232 or RS-485 serial port.
+    $ref: /schemas/types.yaml#/definitions/string
+    enum: [ RS-232, RS-485 ]
+    default: RS-485
+
+required:
+  - compatible
+  - reg
+  - interrupts
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    serial@80000000 {
+      compatible = "ni,ni16550";
+      reg = <0x80000000 0x8>;
+      interrupts = <0 30 IRQ_TYPE_LEVEL_HIGH>;
+      clocks = <&clk_uart>;
+      ni,serial-port-mode = "RS-232";
+    };
+...
-- 
2.30.2

On Mon, Oct 23, 2023 at 04:04:56PM -0500, Brenda Streiff wrote:
> Add bindings for the NI 16550 UART.
> 
> Signed-off-by: Brenda Streiff <brenda.streiff@ni.com>
> Cc: Gratian Crisan <gratian.crisan@ni.com>
> Cc: Jason Smith <jason.smith@ni.com>
> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> ---
>  .../bindings/serial/ni,ni16550.yaml           | 51 +++++++++++++++++++
>  1 file changed, 51 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/serial/ni,ni16550.yaml
> 
> diff --git a/Documentation/devicetree/bindings/serial/ni,ni16550.yaml b/Documentation/devicetree/bindings/serial/ni,ni16550.yaml
> new file mode 100644
> index 000000000000..72ab125dd892
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/serial/ni,ni16550.yaml
> @@ -0,0 +1,51 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/serial/ni,ni16550.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: NI 16550 asynchronous serial interface (UART)

Is this significantly different than all the other 8250 compatible UARTs 
in 8250.yaml?

> +
> +maintainers:
> +  - Brenda Streiff <brenda.streiff@ni.com>
> +
> +allOf:
> +  - $ref: serial.yaml#
> +
> +properties:
> +  compatible:
> +    const: ni,ni16550
> +
> +  reg:
> +    maxItems: 1
> +
> +  interrupts:
> +    maxItems: 1
> +
> +  clocks:
> +    maxItems: 1
> +
> +  ni,serial-port-mode:
> +    description: Indicates whether this is an RS-232 or RS-485 serial port.
> +    $ref: /schemas/types.yaml#/definitions/string
> +    enum: [ RS-232, RS-485 ]
> +    default: RS-485

We already have 'linux,rs485-enabled-at-boot-time' which seems similar 
purpose. It also tells me this is not a fixed in hardware setting. If 
that property doesn't work for you, come up with something common and 
explain why. Or explain why this is completely unique to this UART.

Rob