内核源代码位置：
linux-3.6.38/drivers/tty/serial/samsung.c
+1550
#if defined(RS485_PORT3) || defined(RS485_PORT2)
static struct proc_dir_entry *gpn12_inode = NULL;
static char msg[10];
static int write_gpn12(struct file *file, const char __user *buffer, unsigned long count, void *data)
{
int status = 0;
if (copy_from_user((void *)msg, (const void __user *)buffer, count))
return -EFAULT;
status = simple_strtoul(msg, NULL, 0);
gpio_direction_output(S3C64XX_GPN(12), status);
return count;
}
#endif