boards: silabs: slstk3701a: Enable LPM013M126A Display

Enable the LPM013M126A display node under USART1 in the slstk3701a DTS.
Add pre_dt_board.cmake to suppress SPI bus bridge warnings, and update the
pinctrl configuration to properly configure the display control pins.

Signed-off-by: Elgin Perumbilly <[email protected]>

Author: Elgin-Perumbilly

boards/silabs/starter_kits/slstk3701a/pre_dt_board.cmake

@@ -0,0 +1,7 @@
+# Copyright (c) 2025 Silicon Signals Pvt. Ltd.
+# SPDX-License-Identifier: Apache-2.0
+
+# SPI functionality is provided via a USART peripheral; the node is named
+# usart@..., not spi@... To suppress the 'spi_bus_reg: Failed prerequisite
+# "spi_bus_bridge"' warning, the -Wno-spi_bus_bridge flag is applied.
+list(APPEND EXTRA_DTC_FLAGS "-Wno-spi_bus_bridge")

boards/silabs/starter_kits/slstk3701a/slstk3701a-pinctrl.dtsi

@@ -52,4 +52,15 @@
 				<GECKO_LOC(UART_RX, 4)>;
 		};
 	};
+
+	usart1_default: usart1_default {
+		group1 {
+			psels = <GECKO_PSEL(SPIM_SCK, C, 15)>,
+				<GECKO_PSEL(SPIM_MISO, A, 0)>,
+				<GECKO_PSEL(SPIM_MOSI, A, 14)>,
+				<GECKO_LOC(SPI_SCK, 3)>,
+				<GECKO_LOC(SPI_MISO, 0)>,
+				<GECKO_LOC(SPI_MOSI, 6)>;
+		};
+	};
 };

boards/silabs/starter_kits/slstk3701a/slstk3701a.dts

@@ -19,6 +19,7 @@
 		zephyr,flash = &flash0;
 		zephyr,shell-uart = &usart4;
 		zephyr,sram = &sram0;
+		zephyr,display = &lpm013m126;
 	};
 
 	/* These aliases are provided for compatibility with samples */
@@ -72,6 +73,27 @@
 	};
 };
 
+&usart1 {
+	compatible = "silabs,usart-spi";
+	#address-cells = <1>;
+	#size-cells = <0>;
+	cs-gpios = <&gpioc 14 GPIO_ACTIVE_HIGH>;
+	pinctrl-0 = <&usart1_default>;
+	pinctrl-names = "default";
+	status = "okay";
+
+	lpm013m126: lpm013m126@0 {
+		compatible = "jdi,lpm013m126";
+		reg = <0>;
+		height = <176>;
+		width = <176>;
+		spi-max-frequency = <2000000>;
+		disp-gpios = <&gpioa 9 GPIO_ACTIVE_HIGH>;
+		extcomin-gpios = <&gpioa 11 GPIO_ACTIVE_HIGH>;
+		extcomin-frequency = <60>;
+	};
+};
+
 &usart0 {
 	current-speed = <115200>;
 	pinctrl-0 = <&usart0_default>;