LCD背光驱动在2440上的实例开发

一、实现步骤

1. 硬件原理图分析。由原理图得知LCD的背光是由2440的GPG4口控制的

2. 编写背光驱动。文件名为my2440_backlight.c

 

#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/input.h>
#include <linux/init.h>
#include <linux/serio.h>
#include <linux/delay.h>
#include <linux/clk.h>
#include <linux/miscdevice.h>

#include <asm/io.h>
#include <asm/irq.h>
#include <asm/uaccess.h>
#include <mach/regs-clock.h>
#include <plat/regs-timer.h>
#include <mach/regs-gpio.h>
#include <linux/cdev.h>

#define DEVICE_NAME "backlight" //设备名称
#define DEVICE_MINOR 5 //次设备号，这里我们将设备注册为misc设备，这种设备的主设备号都为10

static int my2440_backlight_ioctl(struct inode *inode,

                                  struct file *file,

                                  unsigned int cmd,

                                  unsigned long arg)
{
    switch(cmd)
    {
        case 0:

            //当接收的命令为0时，就将GPG4引脚设为低电平，关闭背光
            s3c2410_gpio_setpin(S3C2410_GPG4, 0); 
            printk(DEVICE_NAME " turn off!\n");
            return 0;
        case 1:

            //当接收的命令为1时，就将GPG4引脚设为高电平，开启背光
            s3c2410_gpio_setpin(S3C2410_GPG4, 1); 
            printk(DEVICE_NAME " turn on!\n");
            return 0;
        default:
            return -EINVAL;
    }
}

static struct file_operations dev_fops =
{
    .owner = THIS_MODULE,
    .ioctl = my2440_backlight_ioctl, //这里只使用控制IO口的方式来控制背光
};

static struct miscdevice misc =
{
    .minor = DEVICE_MINOR,
    .name = DEVICE_NAME,
    .fops = &dev_fops,
};

static int __init dev_init(void)
{
    int ret;

    ret = misc_register(&misc); //注册成misc设备

    if(ret < 0)
    {
        printk("Register misc device fiald!");
        return ret;
    }


    //将GPG4口配置成输出口
    s3c2410_gpio_cfgpin(S3C2410_GPG4, S3C2410_GPG4_OUTP); 

    return ret;
}

static void __exit dev_exit(void)
{
    misc_deregister(&misc); //注销该misc设备
}

module_init(dev_init);
module_exit(dev_exit);

MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("apple");
MODULE_DESCRIPTION("Backlight control for my2440");

3. 将驱动添加到内核中，这里我们将采用静态加载的方法。

   将my2440_backlight.c复制到内核drivers/video/backlight/目录下

#cp -f my2440_backlight.c linux-2.6.30.4/drivers/video/backlight/

   修改backlight/目录下的Kconfig文件，添加背光选项

#gedit linux-2.6.30.4/drivers/video/backlight/Kconfig

config MY2440_LCD_BACKLIGHT
    tristate "My2440 LCD Backlight Controls"
    depends on BACKLIGHT_LCD_SUPPORT
    default y

   修改backlight/目录下的Makefile文件，在最后一行添加

#gedit linux-2.6.30.4/drivers/video/backlight/Makefile

obj-$(CONFIG_MY2440_LCD_BACKLIGHT) += my2440_backlight.o

4. 配置内核选项，选中上面添加的配置项

Device Drivers --->
    Graphics support --->
        [*] Backlight & LCD device support --->
            --- Backlight & LCD device support
            <*> My2440 LCD Backlight Controls (NEW)
            < > Lowlevel LCD controls
            < > Lowlevel Backlight controls

5. 重新编译内核并下载到开发板上，在开发板/dev/目录下建立设备的节点。设备名为backlight，主设备号为10，次设备号为5，在驱动源码里有注释

#mknod /dev/backlight c 10 5

6. 编写应用程序测试背光驱动，文件名为backlight_test.c

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/ioctl.h>

int main(int argc, char **argv)
{
    int turn;
    int fd;
    
    //检测命令后面带的参数
    if(argc == 1 || argc > 2)
    {
        printf("Usage: backlight on|off!\n");
        exit(1);
    }
    
    //打开背光设备
    fd = open("/dev/backlight", O_RDWR);
    
    if(fd < 0)
    {
        printf("Open Backlight Device Faild!\n");
        exit(1);
    }
    
    //判断输入的参数
    if(strcmp(argv[1], "on") == 0)
    {
        turn = 1;
    }
    else if(strcmp(argv[1], "off") == 0)
    {
        turn = 0;
    }
    else
    {
        printf("Usage: backlight on|off!\n");
        exit(1);
    }
    
    //进行IO控制
    ioctl(fd, turn);

    //关闭背光设备
    close(fd);

    return 0;
}

7. 交叉编译应用程序，并下载到开发板的/usr/sbin/目录下

#arm-linux-gcc -o backlight_test backlight_test.c

8. 运行效果。执行应用程序时内核都会打印出背光状态信息，同时观察LCD的背光也得到了控制