Linux设备树
Linux设备树详解及实例
1. 设备树概述
设备树（Device Tree）是一种描述硬件配置的数据结构，用于将硬件信息从内核代码中分离出来。
1.1 设备树基本概念
- 源文件：
.dts- 设备树源文件，.dtsi- 包含文件 - 编译文件：
.dtb- 设备树二进制文件 - 节点：描述设备或总线的基本单位
- 属性：描述设备的特性、地址、中断等
1.2 设备树优势
- 硬件信息与内核代码分离
- 支持同一内核镜像在不同硬件平台运行
- 简化BSP（板级支持包）开发
2. 设备树语法基础
2.1 基本结构
// 示例：简单的设备树
/dts-v1/;
/ {
// 根节点
compatible = "vendor,board-name", "vendor,board-family";
model = "Vendor Board Version 1.0";
#address-cells = <1>; // 子节点地址用1个32位数字表示
#size-cells = <1>; // 子节点大小用1个32位数字表示
// CPU节点
cpus {
#address-cells = <1>;
#size-cells = <0>;
cpu@0 {
compatible = "arm,cortex-a53";
device_type = "cpu";
reg = <0x0>;
clock-frequency = <1200000000>;
};
};
// 内存节点
memory@80000000 {
device_type = "memory";
reg = <0x80000000 0x40000000>; // 起始地址0x80000000，大小1GB
};
// 保留内存
reserved-memory {
#address-cells = <1>;
#size-cells = <1>;
ranges;
linux,cma {
compatible = "shared-dma-pool";
reusable;
size = <0x10000000>; // 256MB
alignment = <0x2000>;
linux,cma-default;
};
};
};
2.2 常用属性详解
/ {
// 兼容性属性 - 最重要的属性
compatible = "vendor,board", "vendor,soc", "arm,board";
// 模型描述
model = "Vendor Development Board";
// 地址和大小单元定义
#address-cells = <1>; // 地址用1个cell表示
#size-cells = <1>; // 大小用1个cell表示
// 中断控制器属性
interrupt-parent = <&intc>; // 指向中断控制器
// 选择总线
chosen {
bootargs = "console=ttyS0,115200 root=/dev/mmcblk0p2 rootwait";
stdout-path = &uart0;
};
// 别名
aliases {
serial0 = &uart0;
ethernet0 = ð0;
mmc0 = &sdhci0;
};
};
3. 常用设备节点实例
3.1 UART串口设备
/ {
soc {
#address-cells = <1>;
#size-cells = <1>;
compatible = "simple-bus";
ranges;
uart0: serial@10000000 {
compatible = "vendor,uart", "ns16550a";
reg = <0x10000000 0x1000>;
interrupts = <0 10 4>; // SPI 10, 电平触发
clocks = <&clk_uart>;
clock-frequency = <115200>;
status = "okay";
// FIFO设置
fifo-size = <16>;
auto-flow-control;
};
uart1: serial@10001000 {
compatible = "vendor,uart";
reg = <0x10001000 0x1000>;
interrupts = <0 11 4>;
clocks = <&clk_uart>;
status = "disabled"; // 默认禁用
};
};
};
3.2 I2C控制器及设备
/ {
soc {
i2c0: i2c@20000000 {
compatible = "vendor,i2c";
#address-cells = <1>;
#size-cells = <0>;
reg = <0x20000000 0x1000>;
interrupts = <0 20 4>;
clocks = <&clk_i2c>;
clock-frequency = <100000>; // 标准模式100kHz
status = "okay";
// I2C设备：EEPROM
eeprom@50 {
compatible = "atmel,24c02";
reg = <0x50>;
pagesize = <16>;
};
// I2C设备：温度传感器
temp_sensor: lm75@48 {
compatible = "national,lm75";
reg = <0x48>;
};
// I2C设备：RTC
rtc: ds1339@68 {
compatible = "dallas,ds1339";
reg = <0x68>;
};
};
i2c1: i2c@20001000 {
compatible = "vendor,i2c";
#address-cells = <1>;
#size-cells = <0>;
reg = <0x20001000 0x1000>;
interrupts = <0 21 4>;
clocks = <&clk_i2c>;
clock-frequency = <400000>; // 快速模式400kHz
status = "okay";
// I2C设备：音频编解码器
codec: wm8960@1a {
compatible = "wlf,wm8960";
reg = <0x1a>;
#sound-dai-cells = <0>;
};
};
};
};
3.3 SPI控制器及设备
/ {
soc {
spi0: spi@30000000 {
compatible = "vendor,spi";
#address-cells = <1>;
#size-cells = <0>;
reg = <0x30000000 0x1000>;
interrupts = <0 30 4>;
clocks = <&clk_spi>;
num-cs = <2>; // 2个片选信号
status = "okay";
// SPI Flash设备
flash@0 {
compatible = "jedec,spi-nor";
reg = <0>; // CS0
spi-max-frequency = <50000000>;
#address-cells = <1>;
#size-cells = <1>;
partition@0 {
label = "bootloader";
reg = <0x00000000 0x00100000>;
};
partition@100000 {
label = "kernel";
reg = <0x00100000 0x00500000>;
};
partition@600000 {
label = "rootfs";
reg = <0x00600000 0x01a00000>;
};
};
// SPI ADC设备
adc@1 {
compatible = "ti,adc128s052";
reg = <1>; // CS1
spi-max-frequency = <1000000>;
vref-supply = <&vref_reg>;
};
};
};
};
3.4 GPIO控制器
/ {
soc {
gpio0: gpio@40000000 {
compatible = "vendor,gpio";
reg = <0x40000000 0x1000>;
interrupts = <0 40 4>;
#gpio-cells = <2>;
gpio-controller;
#interrupt-cells = <2>;
interrupt-controller;
ngpios = <32>;
status = "okay";
};
gpio1: gpio@40001000 {
compatible = "vendor,gpio";
reg = <0x40001000 0x1000>;
interrupts = <0 41 4>;
#gpio-cells = <2>;
gpio-controller;
#interrupt-cells = <2>;
interrupt-controller;
ngpios = <16>;
status = "okay";
};
};
};
3.5 以太网控制器
/ {
soc {
eth0: ethernet@50000000 {
compatible = "vendor,eth";
reg = <0x50000000 0x1000>;
interrupts = <0 50 4>;
clocks = <&clk_eth>;
phy-mode = "rgmii";
phy-handle = <&phy0>;
status = "okay";
mdio {
#address-cells = <1>;
#size-cells = <0>;
phy0: ethernet-phy@0 {
reg = <0>;
reset-gpios = <&gpio0 15 GPIO_ACTIVE_LOW>;
reset-assert-us = <10000>;
reset-deassert-us = <10000>;
};
};
};
};
};
4. 时钟和电源管理
4.1 时钟控制器
/ {
clocks {
#address-cells = <1>;
#size-cells = <1>;
ranges;
osc24m: osc24m {
compatible = "fixed-clock";
#clock-cells = <0>;
clock-frequency = <24000000>;
clock-output-names = "osc24m";
};
clk_pll: pll@10010000 {
compatible = "vendor,pll";
reg = <0x10010000 0x1000>;
#clock-cells = <1>;
clocks = <&osc24m>;
clock-output-names = "pll_cpu", "pll_ddr", "pll_periph";
};
clk_uart: uart_clk {
compatible = "fixed-factor-clock";
#clock-cells = <0>;
clocks = <&clk_pll 2>;
clock-div = <4>;
clock-mult = <1>;
clock-output-names = "uart_clk";
};
};
};
4.2 电源管理
/ {
regulators {
compatible = "simple-bus";
#address-cells = <1>;
#size-cells = <0>;
reg_3v3: regulator@0 {
compatible = "regulator-fixed";
reg = <0>;
regulator-name = "3V3";
regulator-min-microvolt = <3300000>;
regulator-max-microvolt = <3300000>;
regulator-always-on;
};
reg_1v8: regulator@1 {
compatible = "regulator-fixed";
reg = <1>;
regulator-name = "1V8";
regulator-min-microvolt = <1800000>;
regulator-max-microvolt = <1800000>;
gpio = <&gpio0 12 GPIO_ACTIVE_HIGH>;
enable-active-high;
};
vref_reg: regulator@2 {
compatible = "regulator-fixed";
reg = <2>;
regulator-name = "vref";
regulator-min-microvolt = <2500000>;
regulator-max-microvolt = <2500000>;
};
};
};
5. 引脚控制（Pinctrl）
5.1 引脚复用配置
/ {
soc {
pinctrl: pinctrl@60000000 {
compatible = "vendor,pinctrl";
reg = <0x60000000 0x1000>;
// UART0引脚配置
uart0_pins: uart0-pins {
pins = "PA0", "PA1";
function = "uart0";
bias-disable;
};
// I2C0引脚配置
i2c0_pins: i2c0-pins {
pins = "PA2", "PA3";
function = "i2c0";
bias-pull-up;
};
// SPI0引脚配置
spi0_pins: spi0-pins {
pins = "PA4", "PA5", "PA6", "PA7";
function = "spi0";
bias-disable;
};
// 以太网引脚配置
eth_pins: eth-pins {
pins = "PB0", "PB1", "PB2", "PB3",
"PB4", "PB5", "PB6", "PB7",
"PB8", "PB9", "PB10", "PB11";
function = "eth";
drive-strength = <40>;
bias-disable;
};
// LED引脚配置
led_pins: led-pins {
pins = "PC0", "PC1", "PC2";
function = "gpio";
bias-pull-up;
output-high;
};
};
// 在设备节点中引用pinctrl
uart0: serial@10000000 {
compatible = "vendor,uart";
reg = <0x10000000 0x1000>;
interrupts = <0 10 4>;
clocks = <&clk_uart>;
pinctrl-names = "default";
pinctrl-0 = <&uart0_pins>;
status = "okay";
};
i2c0: i2c@20000000 {
compatible = "vendor,i2c";
reg = <0x20000000 0x1000>;
interrupts = <0 20 4>;
clocks = <&clk_i2c>;
pinctrl-names = "default";
pinctrl-0 = <&i2c0_pins>;
status = "okay";
};
};
};
6. 完整开发板实例
6.1 完整的开发板设备树
// vendor-board-v1.dts
/dts-v1/;
#include "vendor-soc.dtsi" // 包含SoC通用定义
/ {
model = "Vendor Development Board V1.0";
compatible = "vendor,board-v1", "vendor,soc";
// 内存配置
memory@80000000 {
device_type = "memory";
reg = <0x80000000 0x40000000>; // 1GB RAM
};
// 保留内存
reserved-memory {
#address-cells = <1>;
#size-cells = <1>;
ranges;
// CMA区域
linux,cma {
compatible = "shared-dma-pool";
reusable;
size = <0x10000000>; // 256MB
alignment = <0x2000>;
linux,cma-default;
};
// DSP专用内存
dsp_reserved: dsp@88000000 {
reg = <0x88000000 0x08000000>; // 128MB
no-map;
};
};
// 启动参数
chosen {
bootargs = "console=ttyS0,115200 earlycon root=/dev/mmcblk0p2 rootwait";
stdout-path = "serial0:115200n8";
};
// 别名
aliases {
serial0 = &uart0;
serial1 = &uart1;
ethernet0 = ð0;
mmc0 = &sdhci0;
spi0 = &spi0;
i2c0 = &i2c0;
i2c1 = &i2c1;
};
// LED定义
leds {
compatible = "gpio-leds";
led-0 {
label = "heartbeat";
gpios = <&gpio0 0 GPIO_ACTIVE_HIGH>;
linux,default-trigger = "heartbeat";
default-state = "off";
};
led-1 {
label = "mmc0";
gpios = <&gpio0 1 GPIO_ACTIVE_HIGH>;
linux,default-trigger = "mmc0";
default-state = "off";
};
led-2 {
label = "cpu";
gpios = <&gpio0 2 GPIO_ACTIVE_HIGH>;
linux,default-trigger = "cpu0";
default-state = "off";
};
};
// 按键定义
gpio-keys {
compatible = "gpio-keys";
button-0 {
label = "User Button 0";
gpios = <&gpio0 3 GPIO_ACTIVE_LOW>;
linux,code = <KEY_PROG1>;
};
button-1 {
label = "User Button 1";
gpios = <&gpio0 4 GPIO_ACTIVE_LOW>;
linux,code = <KEY_PROG2>;
};
};
// 背光控制
backlight: backlight {
compatible = "pwm-backlight";
pwms = <&pwm 0 50000 0>; // PWM通道0，50kHz
brightness-levels = <0 4 8 16 32 64 128 255>;
default-brightness-level = <6>;
enable-gpios = <&gpio0 5 GPIO_ACTIVE_HIGH>;
};
// 音频编解码器
sound {
compatible = "simple-audio-card";
simple-audio-card,name = "Vendor-Board-Sound";
simple-audio-card,format = "i2s";
simple-audio-card,mclk-fs = <256>;
simple-audio-card,cpu {
sound-dai = <&i2s0>;
};
simple-audio-card,codec {
sound-dai = <&codec>;
};
};
};
// 启用/禁用具体设备
&uart0 {
pinctrl-names = "default";
pinctrl-0 = <&uart0_pins>;
status = "okay";
};
&uart1 {
status = "disabled"; // 默认禁用UART1
};
&i2c0 {
pinctrl-names = "default";
pinctrl-0 = <&i2c0_pins>;
status = "okay";
// 扩展板上的设备
expansion_eeprom: eeprom@50 {
compatible = "atmel,24c02";
reg = <0x50>;
pagesize = <16>;
};
};
&i2c1 {
pinctrl-names = "default";
pinctrl-0 = <&i2c1_pins>;
status = "okay";
// 音频编解码器
codec: wm8960@1a {
compatible = "wlf,wm8960";
reg = <0x1a>;
#sound-dai-cells = <0>;
};
};
&spi0 {
pinctrl-names = "default";
pinctrl-0 = <&spi0_pins>;
status = "okay";
flash@0 {
compatible = "winbond,w25q128", "jedec,spi-nor";
reg = <0>;
spi-max-frequency = <50000000>;
#address-cells = <1>;
#size-cells = <1>;
partition@0 {
label = "bootloader";
reg = <0x000000 0x100000>;
};
partition@100000 {
label = "kernel";
reg = <0x100000 0x500000>;
};
partition@600000 {
label = "rootfs";
reg = <0x600000 0xa00000>;
};
};
};
ð0 {
pinctrl-names = "default";
pinctrl-0 = <ð_pins>;
phy-mode = "rgmii";
status = "okay";
fixed-link {
speed = <1000>;
full-duplex;
};
};
&sdhci0 {
pinctrl-names = "default";
pinctrl-0 = <&sdhci0_pins>;
bus-width = <4>;
cd-gpios = <&gpio0 6 GPIO_ACTIVE_LOW>;
wp-gpios = <&gpio0 7 GPIO_ACTIVE_HIGH>;
status = "okay";
};
&usb0 {
dr_mode = "host";
status = "okay";
};
&pwm {
pinctrl-names = "default";
pinctrl-0 = <&pwm0_pins>;
status = "okay";
};
7. 设备树驱动实例
7.1 解析设备树的驱动程序
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/of.h>
#include <linux/of_device.h>
#include <linux/gpio/consumer.h>
#include <linux/regulator/consumer.h>
struct my_device_data {
struct device *dev;
void __iomem *regs;
struct gpio_desc *reset_gpio;
struct regulator *vcc_supply;
int irq;
u32 clock_frequency;
const char *device_name;
};
static const struct of_device_id my_device_of_match[] = {
{ .compatible = "vendor,my-device" },
{ .compatible = "vendor,my-device-v2" },
{},
};
MODULE_DEVICE_TABLE(of, my_device_of_match);
static int my_device_parse_dt(struct platform_device *pdev,
struct my_device_data *data)
{
struct device_node *np = pdev->dev.of_node;
int ret;
if (!np) {
dev_err(&pdev->dev, "No device tree node found\n");
return -EINVAL;
}
// 获取设备名称
ret = of_property_read_string(np, "device-name", &data->device_name);
if (ret) {
data->device_name = "default";
}
// 获取时钟频率
ret = of_property_read_u32(np, "clock-frequency", &data->clock_frequency);
if (ret) {
data->clock_frequency = 1000000; // 默认1MHz
}
// 获取GPIO
data->reset_gpio = devm_gpiod_get_optional(&pdev->dev, "reset",
GPIOD_OUT_HIGH);
if (IS_ERR(data->reset_gpio)) {
return PTR_ERR(data->reset_gpio);
}
// 获取电源
data->vcc_supply = devm_regulator_get_optional(&pdev->dev, "vcc");
if (IS_ERR(data->vcc_supply)) {
if (PTR_ERR(data->vcc_supply) == -EPROBE_DEFER)
return -EPROBE_DEFER;
data->vcc_supply = NULL;
}
// 获取中断
data->irq = platform_get_irq(pdev, 0);
if (data->irq < 0) {
dev_info(&pdev->dev, "No IRQ specified\n");
}
return 0;
}
static int my_device_probe(struct platform_device *pdev)
{
struct my_device_data *data;
int ret;
data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
if (!data)
return -ENOMEM;
data->dev = &pdev->dev;
// 解析设备树
ret = my_device_parse_dt(pdev, data);
if (ret)
return ret;
// 映射寄存器
data->regs = devm_platform_ioremap_resource(pdev, 0);
if (IS_ERR(data->regs))
return PTR_ERR(data->regs);
// 使能电源
if (data->vcc_supply) {
ret = regulator_enable(data->vcc_supply);
if (ret) {
dev_err(&pdev->dev, "Failed to enable regulator\n");
return ret;
}
}
// 硬件复位
if (data->reset_gpio) {
gpiod_set_value_cansleep(data->reset_gpio, 0);
msleep(10);
gpiod_set_value_cansleep(data->reset_gpio, 1);
msleep(100);
}
platform_set_drvdata(pdev, data);
dev_info(&pdev->dev, "Device %s probed, clock: %u Hz\n",
data->device_name, data->clock_frequency);
return 0;
}
static int my_device_remove(struct platform_device *pdev)
{
struct my_device_data *data = platform_get_drvdata(pdev);
if (data->vcc_supply)
regulator_disable(data->vcc_supply);
return 0;
}
static struct platform_driver my_device_driver = {
.probe = my_device_probe,
.remove = my_device_remove,
.driver = {
.name = "my-device",
.of_match_table = my_device_of_match,
},
};
module_platform_driver(my_device_driver);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("Device Tree aware device driver");
8. 设备树编译和调试
8.1 编译设备树
# Makefile示例
DTC = dtc
DTS = vendor-board-v1.dts
DTB = vendor-board-v1.dtb
all: $(DTB)
$(DTB): $(DTS)
$(DTC) -I dts -O dtb -o $(DTB) $(DTS)
clean:
rm -f $(DTB)
# 内核中的编译
obj-y += vendor-board-v1.dtb
8.2 设备树调试命令
# 查看设备树
cat /proc/device-tree/model
ls /proc/device-tree/
# 使用dtc工具反编译
dtc -I fs /proc/device-tree
# 查看特定设备
find /proc/device-tree -name "*uart*"
# 内核启动参数添加设备树调试
bootargs="console=ttyS0,115200 earlycon devicetree=debug"
设备树是现代Linux嵌入式系统的核心组成部分，通过合理设计设备树结构，可以创建高度可移植和可维护的硬件描述。掌握设备树语法和驱动程序的设备树解析是嵌入式Linux开发的重要技能。
本文是原创文章，采用 CC BY-NC-ND 4.0 协议，完整转载请注明来自 恒星不见
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