1. 方案背景
产品使用的RK3399核心板，电路板外围电路及模块功能自定义，项目需要增加gpio控制的功能。 由于在用户空间，通过系统命令的方式控制GPIO，拉高拉低的速度响应速度比较慢，而通过内核驱动的方式较快，所以需要开发个内核驱动来控制GPIO。
注意，本文使用的是gpio68号引脚，并非控制所有引脚。
2. 编译及驱动源码
1. kernel/drivers/char/Makefile 添加gpio68.o的编译
obj-y += gpio68.o
2. 新建 kernel/drivers/char/gpio68.c 源码文件。
gpio68.c 源码如下：
#include <linux/module.h> /* For module specific items */
#include <linux/moduleparam.h> /* For new moduleparam's */
#include <linux/types.h> /* For standard types (like size_t) */
#include <linux/errno.h> /* For the -ENODEV/... values */
#include <linux/kernel.h> /* For printk/panic/... */
#include <linux/fs.h> /* For file operations */
#include <linux/ioport.h> /* For io-port access */
#include <linux/platform_device.h> /* For platform_driver framework */
#include <linux/init.h> /* For __init/__exit/... */
#include <linux/uaccess.h> /* For copy_to_user/put_user/... */
#include <linux/io.h> /* For inb/outb/... */
#include <linux/gpio.h>
#include <linux/device.h>
#include <linux/cdev.h>
#include <linux/slab.h> /*kamlloc */
#include <asm-generic/ioctl.h>
//ioctl
#define CMD_FLAG 'i'
#define gpio_PWR_ON _IOR(CMD_FLAG,0x00000001,__u32)
#define gpio_PWR_OFF _IOR(CMD_FLAG,0x00000000,__u32)
#define gpio_lp 68
static int major =0;
static struct class *gpio_class;
struct cdev_gpio {
struct cdev cdev;
};
struct cdev_gpio *gpio_dev;
static long gpio_ioctl(struct file* filp, unsigned int cmd,unsigned long argv)
{
printk(KERN_INFO "entry kernel.... \n");
//printk(KERN_INFO "%d\n", gpio_PWR_ON);
//void __iomem *ldo_mmio_base = ioremap(0xe46002e4, 4);
switch(cmd)
{
case gpio_PWR_ON:
{
gpio_set_value(gpio_lp,1); //
printk(KERN_INFO "gpio on\n");
//iowrite32(0x1700, ldo_mmio_base)
break;
}
case gpio_PWR_OFF:
{
gpio_set_value(gpio_lp,0);
printk(KERN_INFO "gpio off \n");
//iowrite32(0x1500, ldo_mmio_base);
break;
}
default:
return -EINVAL;
}
return 0;
}
//open
static int gpio_open(struct inode* i_node,struct file* filp)
{
//printk(KERN_INFO "open init.... \n");
int err = gpio_request(gpio_lp,"gpio_pwr");
if(err<0)
{
printk(KERN_INFO "gpio request faile \n");
return err;
}
gpio_direction_output(gpio_lp,1);
return 0;
}
//close
static int gpio_close(struct inode* i_node,struct file* filp)
{
printk(KERN_INFO "close init \n");
gpio_free(gpio_lp);
return 0;
}
/* file operations */
struct file_operations fops={
.owner = THIS_MODULE,
.open = gpio_open,
.unlocked_ioctl = gpio_ioctl,
.release = gpio_close,
};
static int __init gpio_init(void)
{
//printk(KERN_INFO "init .... \n");
dev_t dev_no;
int result,err;
err = alloc_chrdev_region(&dev_no,0,1,"my_gpio"); //dynamic request device number
if(err<0)
{
printk(KERN_INFO "ERROR\n");
return err;
}
major = MAJOR(dev_no);
gpio_dev = kmalloc(sizeof(struct cdev_gpio),GFP_KERNEL);
if(!gpio_dev)
{
result = -ENOMEM;
goto fail_malloc;
}
memset(gpio_dev,0,sizeof(*gpio_dev));
cdev_init(&gpio_dev->cdev,&fops);
gpio_dev->cdev.owner = THIS_MODULE;
result = cdev_add(&gpio_dev->cdev,dev_no,1);
if(result <0)
{ printk(KERN_INFO "error\n");
goto fail_add;
}
gpio_class = class_create(THIS_MODULE,"mtgpio68"); //in sys/class create sysfs file
device_create(gpio_class,NULL,MKDEV(major,0),NULL,"gpio68"); //dynamic create device file /dev/mygpio
return 0;
fail_add:
kfree(gpio_dev);
fail_malloc:
unregister_chrdev_region(dev_no,1);
return result;
}
static void __exit gpio_exit(void)
{
dev_t dev_no=MKDEV(major,0);
unregister_chrdev_region(dev_no,1);
cdev_del(&gpio_dev->cdev);
kfree(gpio_dev);
device_destroy(gpio_class,dev_no);
class_destroy(gpio_class);
printk(KERN_INFO "exit........ \n");
}
module_init(gpio_init);
module_exit(gpio_exit);
MODULE_AUTHOR("");
MODULE_DESCRIPTION("control_gpio68");
MODULE_LICENSE("GPL");
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