linux led 驱动

前言

今天是儿童节，挣个奖牌给小孩玩玩。

在 linux 驱动大家庭中，LED 驱动算是个儿童，今天就写写他吧。正好之前写过他的婴儿时期《i.MX6ULL 裸机点亮 LED》，记得那时候他还穿着开裆裤呢，裸鸡嘛。

ioremap()

裸机程序也好、linux 驱动程序也好，最终都是要操作真实设备的，那就要操作物理地址（设备寄存器）。之前写裸机程序，由于没有开启 MMU，CPU 操作的地址就是物理地址。现在写 linux 驱动程序不一样了，内核（包括驱动）操作的都是虚拟地址而无法直接操作物理地址。要想操作物理地址，就要上一个大杀器：ioremap()，可以参考我之前的一篇文章《ioremap()》，这里就不多介绍了。

代码

led.c

#include <asm/io.h>
#include <asm/mach/map.h>
#include <asm/uaccess.h>
#include <linux/delay.h>
#include <linux/errno.h>
#include <linux/gpio.h>
#include <linux/ide.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/types.h>#define LED_MAJOR 200  /* 主设备号 */
#define LED_NAME "led" /* 字符设备名称： cat /proc/devices 显示的字符设备名称 */#define LEDOFF 0	   /* 关灯 */
#define LEDON 1		   /* 开灯 *//* 寄存器物理地址 */
#define CCM_CCR_BASE 0x020C4000	 // Clock Controller Module(CCM)
#define CCM_CCGR1 (CCM_CCR_BASE + 0x6C)
#define GPIO1_BASE 0x0209C000
#define GPIO1_DR (GPIO1_BASE + 0x0)
#define GPIO1_GDIR (GPIO1_BASE + 0x4)
#define SW_MUX_CTL_BASE 0x020E0000	// software mux control registers
#define SW_MUX_CTL_PAD_GPIO1_IO03 (SW_MUX_CTL_BASE + 0x68)
#define SW_PAD_CTL_PAD_GPIO1_IO03 (SW_MUX_CTL_BASE + 0x2F4)/* 映射后的寄存器虚拟地址指针 */
static void __iomem *V_CCM_CCGR1;
static void __iomem *V_SW_MUX_GPIO1_IO03;
static void __iomem *V_SW_PAD_GPIO1_IO03;
static void __iomem *V_GPIO1_DR;
static void __iomem *V_GPIO1_GDIR;static int led_open(struct inode *inode, struct file *filp)
{return 0;
}static ssize_t led_read(struct file *filp, char __user *buf, size_t cnt, loff_t *offt)
{return 0;
}void led_switch(u8 sta)
{u32 val;if (sta == LEDON) {val = readl(V_GPIO1_DR);val &= ~(1 << 3);writel(val, V_GPIO1_DR);} else if (sta == LEDOFF) {val = readl(V_GPIO1_DR);val |= (1 << 3);writel(val, V_GPIO1_DR);}
}/** @description		: 向设备写数据* @param - filp 	: 设备文件，表示打开的文件描述符* @param - buf 	: 要写给设备写入的数据* @param - cnt 	: 要写入的数据长度* @param - offt 	: 相对于文件首地址的偏移* @return 			: 写入的字节数，如果为负值，表示写入失败*/
static ssize_t led_write(struct file *filp, const char __user *buf, size_t cnt, loff_t *offt)
{int retvalue;unsigned char databuf[1];unsigned char ledstat;retvalue = copy_from_user(databuf, buf, cnt);if (retvalue < 0) {printk("kernel write failed!\n");return -EFAULT;}ledstat = databuf[0]; /* 获取状态值 */if (ledstat == LEDON) {led_switch(LEDON);	/* 打开LED灯 */} else if (ledstat == LEDOFF) {led_switch(LEDOFF); /* 关闭LED灯 */}return 0;
}static int led_release(struct inode *inode, struct file *filp)
{return 0;
}/* 设备操作函数 */
static struct file_operations led_fops = {.owner = THIS_MODULE,.open = led_open,.read = led_read,.write = led_write,.release = led_release,
};static int __init led_init(void)
{int retvalue = 0;u32 val = 0;/* 1. 寄存器地址映射 */V_CCM_CCGR1 = ioremap(CCM_CCGR1, 4);V_SW_MUX_GPIO1_IO03 = ioremap(SW_MUX_CTL_PAD_GPIO1_IO03, 4);V_SW_PAD_GPIO1_IO03 = ioremap(SW_PAD_CTL_PAD_GPIO1_IO03, 4);V_GPIO1_DR = ioremap(GPIO1_BASE, 4);V_GPIO1_GDIR = ioremap(GPIO1_GDIR, 4);/* 2. 使能GPIO1时钟 */val = readl(V_CCM_CCGR1);val |= (3 << 26);writel(val, V_CCM_CCGR1);/* 3. 设置GPIO1_IO03的复用功能，将其复用为 GPIO1_IO03，最后设置IO属性 */writel(5, V_SW_MUX_GPIO1_IO03);/* 4. 设置GPIO1_IO03为输出功能 */val = readl(V_GPIO1_GDIR);val |= (1 << 3);writel(val, V_GPIO1_GDIR);/* 5. 配置引脚属性，驱动能力、速度、上下拉 */writel(0x10B0, V_SW_PAD_GPIO1_IO03);/* 6. 默认关闭 LED */val = readl(V_GPIO1_DR);val |= (1 << 3);writel(val, V_GPIO1_DR);/* 7. 注册字符设备驱动 */retvalue = register_chrdev(LED_MAJOR, LED_NAME, &led_fops);if (retvalue < 0) {printk("register chrdev failed!\n");return -EIO;}return 0;
}static void __exit led_exit(void)
{/* 取消映射 */iounmap(V_CCM_CCGR1);iounmap(V_SW_MUX_GPIO1_IO03);iounmap(V_SW_PAD_GPIO1_IO03);iounmap(V_GPIO1_DR);iounmap(V_GPIO1_GDIR);/* 注销字符设备驱动 */unregister_chrdev(LED_MAJOR, LED_NAME);
}module_init(led_init);
module_exit(led_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("liyongjun");

led_app.c

#include "fcntl.h"
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "sys/stat.h"
#include "sys/types.h"
#include "unistd.h"#define LEDOFF 0
#define LEDON 1int main(int argc, char *argv[])
{int fd, retvalue;char *filename;unsigned char databuf[1];if (argc != 3) {printf("Usage: %s devfile 0/1\n", argv[0]);return -1;}filename = argv[1];/* 打开设备文件驱动 */fd = open(filename, O_RDWR);if (fd < 0) {printf("file %s open failed!\n", argv[1]);return -1;}/* 要执行的操作：打开或关闭 */databuf[0] = atoi(argv[2]);/* 向 /dev/led 文件写入数据 */retvalue = write(fd, databuf, sizeof(databuf));if (retvalue < 0) {printf("LED Control Failed!\n");close(fd);return -1;}/* 关闭文件 */retvalue = close(fd);if (retvalue < 0) {printf("file %s close failed!\n", argv[1]);return -1;}return 0;
}

Makefile

KERNELDIR := ../../../linux/linux-imx-rel_imx_4.1.15_2.1.0_ga_alientek/
CURRENT_PATH := $(shell pwd)obj-m := led.obuild: kernel_moduleskernel_modules:$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) modulesclean:$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) cleanrm led_appCROSS_COMPILE = ../../../tool/gcc-linaro-4.9.4-2017.01-x86_64_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-gccapp:$(CROSS_COMPILE) led_app.c -o led_appinstall:cp led.ko led_app ../../../rootfs/home/root/

验证

step1：安装驱动程序

insmod led.ko

# cat /proc/devices
Character devices:
1 mem
4 /dev/vc/0
4 tty
5 /dev/tty
5 /dev/console
5 /dev/ptmx
7 vcs
10 misc
13 input
81 video4linux
89 i2c
90 mtd
116 alsa
128 ptm
136 pts
180 usb
189 usb_device
200 led
207 ttymxc

step2：创建字符设备文件

# mknod /dev/led c 200 0
#
# ls -lh /dev/led
crw-r--r-- 1 root root 200, 0 May 31 14:06 /dev/led

step3：执行测试程序

# ./led_app /dev/led 1
# ./led_app /dev/led 0

看到 led 亮、灭