你的第一个Linux设备树驱动程序

进行嵌入式开发的主流方法是使用设备树文件添加设备信息，驱动通过获取设备信息对设备进行操作。下面将演示如何写一个设备树插件文件和驱动代码。在驱动加载的时候读取设备信息，并打印出来。

实验环境

raspberry pi3b

Linux raspberrypi 6.1.21-v8+ #1642 SMP PREEMPT Mon Apr  3 17:24:16 BST 2023 aarch64 GNU/Linux

设备树文件

// testoverlay.dts

/dts-v1/;
/plugin/;
/ {
    compatible = "raspberrypi,3-model-bbrcm,bcm2837";
    fragment@0 {
        target-path = "/";
        __overlay__ {
            my_device {
                compatible = "brightlight,mydev";
                status = "okay";
                label = "test";
                my_value = <12>;
            };
        };
    };
};

• 查看系统设备树信息：cat /proc/device-tree/compatible

raspberrypi,3-model-bbrcm,bcm2837

• 编译：dtc -@ -I dts -O dtb -o testoverlay.dtbo testoverlay.dts

• 安装：sudo dtoverlay testoverlay.dtbo

• 移除：sudo dtoverlay -r testoverlay

• 查看：ls /proc/device-tree/my_device/

compatible  label  my_value  name  status

驱动代码

// simple.c

#include <linux/init.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/of_device.h>
#include <linux/platform_device.h>
#include <linux/property.h>

// 驱动会通过compatible值与设备树节点进行匹配
static struct of_device_id my_driver_ids[] = {
    {
        .compatible = "brightlight,mydev",
    },
    {},
};
MODULE_DEVICE_TABLE(of, my_driver_ids);

static int _dt_probe(struct platform_device *pdev) {
    struct device *dev = &pdev->dev;
    const char *label = NULL;
    int my_value = 0, ret = 0;

    pr_info("simple_dt_probe\n");

    if (!device_property_present(dev, "label")) {
        pr_err("device_property_present 'lable' failed\n");
        return -1;
    }

    if (!device_property_present(dev, "my_value")) {
        pr_err("device_property_present 'my_value' failed\n");
        return -1;
    }

    ret = device_property_read_string(dev, "label", &label);
    if (ret) {
        pr_err("device_property_read_string 'label' failed\n");
        return -1;
    }
    pr_info("lable = %s", label);

    ret = device_property_read_u32(dev, "my_value", &my_value);
    if (ret) {
        pr_err("device_property_read_u32 'my_value' failed\n");
        return -1;
    }
    pr_info("my_value = %d", my_value);

    return 0;
}

static int _dt_remove(struct platform_device *pdev) {
    pr_info("simple_dt_remove\n");

    return 0;
}

// 与设备树节点匹配成功会调用probe函数
static struct platform_driver my_dirver = {
    .probe = _dt_probe,
    .remove = _dt_remove,
    .driver =
        {
            .name = "my_device_driver",
            .of_match_table = my_driver_ids,
        },
};

static int __init simple_init(void) {
    pr_info("simple_init\n");

    if (platform_driver_register(&my_dirver)) {
        pr_err("platform_driver_register error");
        return -1;
    }

    return 0;
}

static void __exit simple_exit(void) {
    pr_info("simple_exit\n");
    platform_driver_unregister(&my_dirver);
}

module_init(simple_init);
module_exit(simple_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("heng30");
MODULE_VERSION("v0.0.1");
MODULE_DESCRIPTION("A simple kernel module");

Makefile编译脚本

#!/bin/sh

top-dir = $(shell pwd)
kernel-version = $(shell uname -r)
kernel-dir ?= /lib/modules/$(kernel-version)/build

obj-m += simple.o

all:
        make -C $(kernel-dir) modules M=$(top-dir)

clean:
        rm -f *.o *.ko *.mod *.mod.c *.order *.symvers
        make -C $(kernel-dir) clean m=$(top-dir)

测试

• 安装驱动：insmod simple_cdev.ko

• 移除驱动：rmmod simple_cdev.ko

• 查看结果：dmesg

[ 9644.677569] simple_init
[ 9644.681462] simple_dt_probe
[ 9644.690272] lable = test
[ 9644.691608] my_value = 12
[ 9686.640179] simple_exit
[ 9686.641797] simple_dt_remove

参考

• 如何使用qemu启动raspi3b进行嵌入式开发？