一、led字符设备驱动实验

驱动模块=内核模块(.ko)+驱动接口(file_operations)

在内核模块入口函数里获得gpio相关寄存器并初始化
构造file_operations接口，并注册到内核
创建设备文件，绑定自定义file_operations接口
应用程序echo通过写设备文件控制硬件led

二、驱动模块初始化

文件夹：/home/geralt/linux_driver/part_3/chrdev.c

#include <linux/module.h>
#include <linux/init.h>
#include <linux/kernel.h>

#include <linux/fs.h>
#include <linux/uaccess.h>
#include <asm/io.h>

#define DEV_MAJOR		0		/* 动态申请主设备号 */
#define DEV_NAME		"red_led" 	/*led设备名字 */

/* GPIO虚拟地址指针 */
static void __iomem *IMX6U_CCM_CCGR1;
static void __iomem *SW_MUX_GPIO1_IO04;
static void __iomem *SW_PAD_GPIO1_IO04;
static void __iomem *GPIO1_DR;
static void __iomem *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 -EFAULT;
}

static ssize_t led_write(struct file *filp, const char __user *buf, size_t cnt, loff_t *offt)
{

	unsigned char databuf[10];

	if(cnt >10)
		cnt =10;
		
    /*从用户空间拷贝数据到内核空间*/
    if(copy_from_user(databuf, buf, cnt)){
		return -EIO;
	}
    	
	if(!memcmp(databuf,"on",2)) {	
		iowrite32(0 << 4, GPIO1_DR);	
	} else if(!memcmp(databuf,"off",3)) {
		iowrite32(1 << 4, GPIO1_DR);
	}
	/*写成功后，返回写入的字数*/
	return cnt;
}

static int led_release(struct inode *inode, struct file *filp)
{
	return 0;
}

/* 自定义led的file_operations 接口*/
static struct file_operations led_fops = {
	.owner = THIS_MODULE,
	.open = led_open,
	.read = led_read,
	.write = led_write,
	.release = 	led_release,
};

int major = 0;
static int __init led_init(void)
{
	
	/* GPIO相关寄存器映射 */
  	IMX6U_CCM_CCGR1 = ioremap(0x20c406c, 4);
	SW_MUX_GPIO1_IO04 = ioremap(0x20e006c, 4);
  	SW_PAD_GPIO1_IO04 = ioremap(0x20e02f8, 4);
	GPIO1_GDIR = ioremap(0x0209c004, 4);
	GPIO1_DR = ioremap(0x0209c000, 4);


	/* 使能GPIO1时钟 */
	iowrite32(0xffffffff, IMX6U_CCM_CCGR1);

	/* 设置GPIO1_IO04复用为普通GPIO*/
	iowrite32(5, SW_MUX_GPIO1_IO04);
	
    /*设置GPIO属性*/
	iowrite32(0x10B0, SW_PAD_GPIO1_IO04);

	/* 设置GPIO1_IO04为输出功能 */
	iowrite32(1 << 4, GPIO1_GDIR);

	/* LED输出高电平 */
	iowrite32(1<< 4, GPIO1_DR);

	/* 注册字符设备驱动 */
	major = register_chrdev(DEV_MAJOR, DEV_NAME, &led_fops);
    printk(KERN_ALERT "led major:%d\n",major);

	return 0;
}

static void __exit led_exit(void)
{
	/* 取消映射 */
	iounmap(IMX6U_CCM_CCGR1);
	iounmap(SW_MUX_GPIO1_IO04);
	iounmap(SW_PAD_GPIO1_IO04);
	iounmap(GPIO1_DR);
	iounmap(GPIO1_GDIR);

	/* 注销字符设备驱动 */
	unregister_chrdev(major, DEV_NAME);
}


module_init(led_init);
module_exit(led_exit);

MODULE_LICENSE("GPL2");
MODULE_AUTHOR("embedfire ");
MODULE_DESCRIPTION("led_module");
MODULE_ALIAS("led_module");

地址映射

GPIO寄存器物理地址和虚拟地址映射

文件夹：ebf-buster-linux/arch/arm/include/asm/io.h()

void __iomem *ioremap(resource_size_t res_cookie, size_t size)

参数

res_cookie:物理地址
size:映射长度

返回值

void *类型的指针：指向被映射的虚拟地址
__iomem:主要用于编译器检查地址在内核空间的有效性

三、虚拟地址读写

readl()/ writel() //过时

void iowrite32(u32 b, void __iomem *addr) //写入一个双字（32bit）

unsigned int ioread32(void __iomem *addr) //读取一个双字（32bit）

内核会检查cpu大小端，调整字节序，以提高驱动的可移植性

四、自定义led的file_operation接口

static struct file_operations led_fops = {

.owner = THIS_MODULE,

.open = led_open,

.read = led_read,

.write = led_write,

.release = led_release,

};

owner：设置驱动接口关联的内核模块，防止驱动程序运行时内核模块被卸载
release：文件引用数为0时调用

五、拷贝数据

文件夹：include/linux/uaccess.h

copy_from_user(void *to, const void __user *from, unsigned long n)

参数：

*to：将数据拷贝到内核的地址
*from：需要拷贝数据的用户空间地址
n：拷贝数据的长度（字节）

返回值

失败：没有被拷贝的字节数
成功：0

六、register_chrdev函数

文件夹：ebf-buster-linux/include/linux/fs.h

作用：注册到内核

static inline int register_chrdev(unsigned int major, const char *name,

const struct file_operations *fops)

{

return __register_chrdev(major, 0, 256, name, fops);

}

七、 __register_chrdev函数

源码文件夹：kernel/ebf-buster-linux/fs/char_dev.c

int __register_chrdev(unsigned int major, unsigned int baseminor,unsigned int count, const char *name,const struct file_operations *fops)

{

struct char_device_struct *cd;

struct cdev *cdev;

int err = -ENOMEM;

cd = __register_chrdev_region(major, baseminor, count, name);

...

cdev = cdev_alloc();

...

cdev->owner = fops->owner;

cdev->ops = fops;

...

err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);

...

}