Device Tree 실전 — DTS·DTB·Overlay·Phandle 추적

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sample.dts    ← human readable source
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  │
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  │ dtc -I dts -O dtb -o sample.dtb sample.dts
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  ↓
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sample.dtb    ← binary blob, bootloader가 kernel에 전달
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  │
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  ↓
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sample.dtbo   ← overlay (run-time merge)

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/dts-v1/;
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/ {
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    model = "MyBoard v1";
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    compatible = "myco,myboard";
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    #address-cells = <1>;
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    #size-cells = <1>;
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    cpus {
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        #address-cells = <1>;
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        #size-cells = <0>;
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        cpu@0 {
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            device_type = "cpu";
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            compatible = "arm,cortex-a72";
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            reg = <0>;
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        };
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    };
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    memory@80000000 {
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        device_type = "memory";
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        reg = <0x80000000 0x80000000>;   // 2 GB at 0x80000000
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    };
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    soc {
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        compatible = "simple-bus";
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        #address-cells = <1>;
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        #size-cells = <1>;
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        ranges;
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        uart0: serial@10000000 {
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            compatible = "ns16550a";
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            reg = <0x10000000 0x100>;
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            interrupts = <23>;
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            clock-frequency = <24000000>;
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            current-speed = <115200>;
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            status = "okay";
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        };
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    };
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};

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#address-cells = <2>;
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#size-cells = <2>;
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memory@0 {
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    reg = <0x0 0x80000000 0x0 0x40000000>;   // address (2 cells) + size (2 cells)
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    /* = 0x0000_0000_8000_0000 길이 0x0000_0000_4000_0000 = 1 GB */
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};

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gpio0: gpio@40020000 {
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    compatible = "snps,dw-apb-gpio";
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    reg = <0x40020000 0x1000>;
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    #gpio-cells = <2>;
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};
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leds {
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    compatible = "gpio-leds";
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    led0 {
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        label = "status";
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        gpios = <&gpio0 12 GPIO_ACTIVE_HIGH>;
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    };
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};

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intc: interrupt-controller@8000000 {
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    compatible = "arm,gic-v3";
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    interrupt-controller;
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    #interrupt-cells = <3>;
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    reg = <0x8000000 0x10000>,
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          <0x8010000 0x100000>;
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};
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uart0: serial@10000000 {
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    interrupts = <GIC_SPI 33 IRQ_TYPE_LEVEL_HIGH>;
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    interrupt-parent = <&intc>;
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};

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pinctrl: pinctrl@40020000 {
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    uart0_pins: uart0-pinmux {
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        pins = "PA9", "PA10";
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        function = "uart";
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        bias-disable;
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    };
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};
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uart0: serial@10000000 {
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    pinctrl-names = "default";
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    pinctrl-0 = <&uart0_pins>;
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};

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&i2c1 {
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    status = "okay";
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    clock-frequency = <400000>;
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    eeprom@50 {
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        compatible = "atmel,24c256";
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        reg = <0x50>;
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        pagesize = <64>;
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    };
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    rtc@68 {
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        compatible = "dallas,ds3231";
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        reg = <0x68>;
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    };
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};
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&spi1 {
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    status = "okay";
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    flash@0 {
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        compatible = "winbond,w25q128";
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        reg = <0>;
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        spi-max-frequency = <50000000>;
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    };
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};

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&uart2 { status = "disabled"; };
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&i2c3 { status = "okay"; };

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compatible = "ti,am335x-uart", "ns16550a";

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static const struct of_device_id my_uart_of_match[] = {
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    { .compatible = "ti,am335x-uart" },
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    { },
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};
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MODULE_DEVICE_TABLE(of, my_uart_of_match);

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static int my_probe(struct platform_device *pdev) {
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    struct device_node *np = pdev->dev.of_node;
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    u32 freq;
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    const char *label;
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    of_property_read_u32(np, "clock-frequency", &freq);
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    of_property_read_string(np, "label", &label);
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    /* MMIO mapping */
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    void __iomem *base = devm_platform_ioremap_resource(pdev, 0);
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    if (IS_ERR(base)) return PTR_ERR(base);
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    /* IRQ */
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    int irq = platform_get_irq(pdev, 0);
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    if (irq < 0) return irq;
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    /* GPIO */
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    struct gpio_desc *gpio = devm_gpiod_get(&pdev->dev, "reset", GPIOD_OUT_LOW);
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    return 0;
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}

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/dts-v1/;
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/plugin/;
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&i2c1 {
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    #address-cells = <1>;
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    #size-cells = <0>;
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    status = "okay";
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    new_sensor: sensor@68 {
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        compatible = "bosch,bmp280";
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        reg = <0x68>;
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    };
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};

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soc {
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    #address-cells = <1>;   // 자식 reg의 address cell 수
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    uart@10000000 {
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        reg = <0x10000000 0x100>;   // 1 address cell + 1 size cell
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    };
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};

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gpio_controller@40020000 {   // ← label 없음
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    /* ... */
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};
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leds {
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    gpios = <&gpio_controller 12 0>;   // ← undefined reference
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};

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gpio_controller: gpio_controller@40020000 { ... };

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&i2c1 {
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    status = "disabled";
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    sensor@50 { ... };   // ← parent disabled, driver probe 안 됨
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};