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按照实例一，实现了从应用程序空间向内核空间传递数据，这一例实现从内核读取按键值到应用空间，然后把刚刚保存在应用空间按键值写到内核空间，内核空间按键值来操作对应的LED

驱动源码：keys_leds.c

驱动源码Makefile

测试源码: keys_leds_test.c

keys_leds.c:

/***************************************************************

*	filename:	keys_leds.c
*	description:	无按键按下，熄灭全部LED，按键按下，点亮相应LED，松开熄灭相应LED
*	author:		xyc
*	create time:	2014/6/2
*	version:1
*	modify info:
******************************************************/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <asm/irq.h>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h>
#include <asm-arm/io.h>
#include <asm-arm/uaccess.h>

static int KEYS_LEDS_MAJOR;
static struct class *keys_leds;
static struct class_device *keys_leds_dev;
static volatile unsigned long *gpfcon=NULL;
static volatile unsigned long *gpfdat=NULL;

static int keys_leds_open(struct inode *inode, struct file *file)
{
	/*配置按键为输入，LED为输出*/

	*gpfcon &= ~(0x3<<(4*2)) & (~(0x3<<(0*2))) & (~(0x3<<(5*2)) ) & (~(0x3<<(2*2)));
	*gpfcon |= 0x1<<(4*2) |(0x0<<(0*2)) | (0x1<<(5*2) )|(0x0<<(2*2));
	*gpfdat |=1<<4|1<<5;	
	return 0;
}

static ssize_t keys_leds_read(struct file *file, char __user *userbuf, size_t count, loff_t *off)
{
	char val =0;//初始化为0不要忘
	/*记录按下的键*/
	if( !(*gpfdat &a