实验目的

点亮龙芯开发板上面的用户自定义LED灯，编写LED驱动以及测试用例验证实现效果，LED位于开发板左下方（靠近USB口）第二个

原理图

LED通过电阻上拉至电源P3V3，低电平时LED被点亮

设备树

打开arch/loongarch/boot/dts/loongson/loongson_2k0300_pai_99.dts，将72-150行的i2c1和i2c2两个节点注释掉，如下所示

将loongson_2k0300_pai_99设备树编译进内核，编译完后将内核scp到开发板的/boot目录下，然后重启开发板

驱动示例

LED驱动

LED对应的GPIO号为83

#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/ide.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/gpio.h>
#include <linux/cdev.h>
#include <linux/device.h>#define GPIOLED_CNT			1		  
#define GPIOLED_NAME		"led"	
#define OFF 				0		
#define ON 					1		
#define GPIO_LED 			83struct my_led_dev{dev_t dev_id;		struct cdev cdev;	struct class *class;	struct device *device;	int major;			int minor;			struct device_node	*nd; int led;		
};struct my_led_dev led_dev;	static int led_open(struct inode *inode, struct file *filp)
{filp->private_data = &led_dev; return 0;
}static ssize_t led_read(struct file *filp, char __user *buf, size_t cnt, loff_t *offt)
{return 0;
}static ssize_t led_write(struct file *filp, const char __user *buf, size_t cnt, loff_t *offt)
{int ret;unsigned char data[1];unsigned char ledstat;struct my_led_dev *dev = filp->private_data;ret = copy_from_user(data, buf, cnt);if(ret < 0) {printk("kernel write failed!\r\n");return -EFAULT;}ledstat = data[0];	if(ledstat == ON) {	gpio_set_value(dev->led, 0);	} else if(ledstat == OFF) {gpio_set_value(dev->led, 1);	}return 0;
}static int led_release(struct inode *inode, struct file *filp)
{return 0;
}static struct file_operations led_dev_fops = {.owner = THIS_MODULE,.open = led_open,.read = led_read,.write = led_write,.release = 	led_release,
};static int __init led_init(void)
{int ret = 0;led_dev.led = GPIO_LED;if(led_dev.led < 0) {printk("can't get led-gpio");return -EINVAL;}ret = gpio_request(led_dev.led, "LED-GPIO");if (ret) {printk(KERN_ERR "led_dev: Failed to request led-gpio\n");return ret;}ret = gpio_direction_output(led_dev.led, 1);if(ret < 0) {printk("can't set gpio!\r\n");}if (led_dev.major) {		led_dev.dev_id = MKDEV(led_dev.major, 0);ret = register_chrdev_region(led_dev.dev_id, GPIOLED_CNT, GPIOLED_NAME);if(ret < 0) {pr_err("cannot register %s char driver [ret=%d]\n", GPIOLED_NAME, GPIOLED_CNT);goto free_gpio;}} else {					ret = alloc_chrdev_region(&led_dev.dev_id, 0, GPIOLED_CNT, GPIOLED_NAME);if(ret < 0) {pr_err("%s Couldn't alloc_chrdev_region, ret=%d\r\n", GPIOLED_NAME, ret);goto free_gpio;}led_dev.major = MAJOR(led_dev.dev_id);	led_dev.minor = MINOR(led_dev.dev_id);	}led_dev.cdev.owner = THIS_MODULE;cdev_init(&led_dev.cdev, &led_dev_fops);cdev_add(&led_dev.cdev, led_dev.dev_id, GPIOLED_CNT);if(ret < 0)goto del_unregister;led_dev.class = class_create(THIS_MODULE, GPIOLED_NAME);if (IS_ERR(led_dev.class)) {goto del_cdev;}led_dev.device = device_create(led_dev.class, NULL, led_dev.dev_id, NULL, GPIOLED_NAME);if (IS_ERR(led_dev.device)) {goto destroy_class;}return 0;destroy_class:class_destroy(led_dev.class);
del_cdev:cdev_del(&led_dev.cdev);
del_unregister:unregister_chrdev_region(led_dev.dev_id, GPIOLED_CNT);
free_gpio:gpio_free(led_dev.led);return -EIO;
}static void __exit led_exit(void)
{cdev_del(&led_dev.cdev);unregister_chrdev_region(led_dev.dev_id, GPIOLED_CNT); device_destroy(led_dev.class, led_dev.dev_id);class_destroy(led_dev.class);gpio_free(led_dev.led); 
}module_init(led_init);
module_exit(led_exit);
MODULE_LICENSE("GPL");

Makefile

跟之前一篇文章的Makefile差不多，这里要改一下驱动名称

obj-m += led.o 
KDIR:=/home/asensing/loongson/linux-4.19
ARCH=loongarch 
CROSS_COMPILE=loongarch64-linux-gnu-
PWD?=$(shell pwd) 
all:make -C $(KDIR) M=$(PWD) modules 

build脚本

分别编译测试用例和驱动模块

export PATH=$PATH:/home/asensing/loongson/loongson-gnu-toolchain-8.3-x86_64-loongarch64-linux-gnu-rc1.3-1/bin
make -j8
loongarch64-linux-gnu-gcc test.c -o test
FILE=$PWD/$(basename $PWD).ko
scp $FILE test root@192.168.137.128:/home/root

测试用例

c代码

#include "stdio.h"
#include "unistd.h"
#include "sys/types.h"
#include "sys/stat.h"
#include "fcntl.h"
#include "stdlib.h"
#include "string.h"
#include "time.h"int main(int argc, char *argv[])
{int fd, ret;char *filename;unsigned char data[1];if(argc != 2){printf("Error Usage!\r\n");return -1;}filename = argv[1];fd = open(filename, O_RDWR);if(fd < 0){printf("file %s open failed!\r\n", argv[1]);return -1;}while(1) {data[0] = 1;ret = write(fd, data, sizeof(data));if(ret < 0){printf("LED Control Failed!\r\n");close(fd);return -1;}usleep(500000);data[0] = 0;ret = write(fd, data, sizeof(data));if(ret < 0){printf("LED Control Failed!\r\n");close(fd);return -1;}usleep(500000);}ret = close(fd);if(ret < 0){printf("file %s close failed!\r\n", argv[1]);return -1;}return 0;
}

① 通过执行上面的build脚本，生成led.ko和test文件

② 插入内核驱动模块led.ko

③ 检查/dev目录是否已经生成设备节点

④ 执行test用例

命令行

在led.ko没有插入的情况下，也可以用以下脚本循环点亮LED灯

while true; 
do echo 1 > /sys/class/gpio/gpio48/value; sleep 0.5; echo 0 > /sys/class/gpio/gpio48/value; sleep 0.5; 
done;

实验效果

可以看到板子左下角第二颗LED被循环点亮