riscv: dts: sophgo: Add Milk-V Duo 256M board support

The Milk-V Duo 256M is a small form factor development board based on
the Sophgo SG2002 SoC.

This patch adds basic device tree support for the board, including:
- UART console
- SD/MMC controller
- USB host
- Onboard blue status LED (connected to PWR_GPIO[2] / porte 2)

Tested on actual Milk-V Duo 256M hardware, verified boot to shell and
heartbeat LED functionality.

Signed-off-by: Chen-Yu Yeh <chenyou910331@gmail.com>
Link: https://patch.msgid.link/20260725175346.139173-4-chenyou910331@gmail.com
Signed-off-by: Inochi Amaoto <inochiama@gmail.com>
Signed-off-by: Chen Wang <chen.wang@linux.dev>

2 files changed, 122 insertions, 0 deletions

diff --git a/arch/riscv/boot/dts/sophgo/Makefile b/arch/riscv/boot/dts/sophgo/Makefile
index 58cc6b70d8de..d5c80d4ff005 100644
--- a/arch/riscv/boot/dts/sophgo/Makefile
+++ b/arch/riscv/boot/dts/sophgo/Makefile
@@ -3,6 +3,7 @@ dtb-$(CONFIG_ARCH_SOPHGO) += cv1800b-milkv-duo.dtb
 dtb-$(CONFIG_ARCH_SOPHGO) += cv1812h-huashan-pi.dtb
 dtb-$(CONFIG_ARCH_SOPHGO) += sg2000-milkv-duo-s.dtb
 dtb-$(CONFIG_ARCH_SOPHGO) += sg2002-licheerv-nano-b.dtb
+dtb-$(CONFIG_ARCH_SOPHGO) += sg2002-milkv-duo256m.dtb
 dtb-$(CONFIG_ARCH_SOPHGO) += sg2042-milkv-pioneer.dtb
 dtb-$(CONFIG_ARCH_SOPHGO) += sg2042-evb-v1.dtb
 dtb-$(CONFIG_ARCH_SOPHGO) += sg2042-evb-v2.dtb
diff --git a/arch/riscv/boot/dts/sophgo/sg2002-milkv-duo256m.dts b/arch/riscv/boot/dts/sophgo/sg2002-milkv-duo256m.dts
new file mode 100644
index 000000000000..a2797c0bd767
--- /dev/null
+++ b/arch/riscv/boot/dts/sophgo/sg2002-milkv-duo256m.dts
@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: (GPL-2.0 OR MIT)
+/*
+ * Copyright (C) 2023 Jisheng Zhang <jszhang@kernel.org>
+ * Copyright (C) 2026 Chen-Yu Yeh <chenyou910331@gmail.com>
+ */
+
+/dts-v1/;
+
+#include "sg2002.dtsi"
+#include <dt-bindings/gpio/gpio.h>
+#include <dt-bindings/leds/common.h>
+
+/ {
+	model = "Milk-V Duo 256M";
+	compatible = "milkv,duo256m", "sophgo,sg2002";
+
+	aliases {
+		serial0 = &uart0;
+		serial1 = &uart1;
+		serial2 = &uart2;
+		serial3 = &uart3;
+		serial4 = &uart4;
+	};
+
+	chosen {
+		stdout-path = "serial0:115200n8";
+	};
+
+	leds {
+		compatible = "gpio-leds";
+
+		led-0 {
+			gpios = <&porte 2 GPIO_ACTIVE_HIGH>;
+			color = <LED_COLOR_ID_BLUE>;
+			function = LED_FUNCTION_STATUS;
+			linux,default-trigger = "heartbeat";
+		};
+	};
+
+	reserved-memory {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		ranges;
+
+		coprocessor_rtos: region@8fe00000 {
+			reg = <0x8fe00000 0x200000>;
+			no-map;
+		};
+	};
+};
+
+&osc {
+	clock-frequency = <25000000>;
+};
+
+&pinctrl {
+	uart0_cfg: uart0-cfg {
+		uart0-pins {
+			pinmux = <PINMUX(PIN_UART0_TX, 0)>,
+				 <PINMUX(PIN_UART0_RX, 0)>;
+			bias-pull-up;
+			drive-strength-microamp = <10800>;
+			power-source = <3300>;
+		};
+	};
+
+	sdhci0_cfg: sdhci0-cfg {
+		sdhci0-clk-pins {
+			pinmux = <PINMUX(PIN_SD0_CLK, 0)>;
+			bias-pull-up;
+			drive-strength-microamp = <16100>;
+			power-source = <3300>;
+		};
+
+		sdhci0-cmd-pins {
+			pinmux = <PINMUX(PIN_SD0_CMD, 0)>;
+			bias-pull-up;
+			drive-strength-microamp = <10800>;
+			power-source = <3300>;
+		};
+
+		sdhci0-data-pins {
+			pinmux = <PINMUX(PIN_SD0_D0, 0)>,
+				 <PINMUX(PIN_SD0_D1, 0)>,
+				 <PINMUX(PIN_SD0_D2, 0)>,
+				 <PINMUX(PIN_SD0_D3, 0)>;
+			bias-pull-up;
+			drive-strength-microamp = <10800>;
+			power-source = <3300>;
+		};
+
+		sdhci0-cd-pins {
+			pinmux = <PINMUX(PIN_SD0_CD, 0)>;
+			bias-pull-up;
+			drive-strength-microamp = <10800>;
+			power-source = <3300>;
+		};
+	};
+};
+
+&sdhci0 {
+	pinctrl-0 = <&sdhci0_cfg>;
+	pinctrl-names = "default";
+	status = "okay";
+	bus-width = <4>;
+	no-1-8-v;
+	no-mmc;
+	no-sdio;
+	disable-wp;
+};
+
+&uart0 {
+	pinctrl-0 = <&uart0_cfg>;
+	pinctrl-names = "default";
+	status = "okay";
+};
+
+&usb {
+	dr_mode = "host";
+	status = "okay";
+};