基于platform简单驱动，probe函数中实现file_operations

在Linux之中，约定如果设备不属于任何的总线，则可以把它注册为虚拟的platform设备。

下面就简单来学习一下一个简单的platform设备是怎么创建出来的。

一般注册platform驱动的步骤是：

1，platform_device_create注册一个设备

2，platform_driver_create注册一个驱动。

static struct platform_driver chrdev_platform_driver = {
    .probe  =   chrdev_probe,
    .remove =   chrdev_remove,
    .driver =   {
        .name   =   CHRDEV_NAME,
        .owner  =   THIS_MODULE,
    },
};

static struct platform_device chrdev_platform_device = {
    .name   =   CHRDEV_NAME,
    .id     =   0,
    .dev    =   {
    }
};

platform_device和platform_driver的名字必须一致

然后在chrdev_probe中完成注册一个字符设备。一般注册字符设备的流程如下：

1，alloc_chrdev_region分配一个未使用的设备号

2，cdev_init和cdev_add使用（1）分配到的设备号添加一个字符设备

如果到这里就结束了，我们就需要使用分配到的设备号手动去建立/dev下面的设备节点，，，

在这里可以使用class_create和device_create让udev deamon自动为我们创建设备节点

3，class_create(THIS_MODULE, "chrdev");

4，device_create(chrdev_class, NULL, chrdev_devno, NULL, "chrdev");

当使用insmod把模块加载到系统之后，www.linuxidc.com 就会在/dev下面自动创建名为"chrdev"的设备节点，模块名字应该尽量跟注册驱动的名字一致，不然可能会遇到不可测的问题。

源文件：chrdev.c

#include
#include
#include
#include
#include

/*
 * Yao.GUET
 * http://blog.csdn.net/Yao_GUET
 * a simple platform character driver
 */

MODULE_LICENSE("Dual BSD/GPL");

static int chrdev_open(struct inode *inode, struct file *file) {
    printk(KERN_ALERT "chrdev open!\n");
    return 0;
}

static int chrdev_release(struct inode *inode, struct file *file) {
    printk(KERN_ALERT "chrdev release!\n");
    return 0;
}

static int chrdev_ioctl(struct inode *inode, struct file *file,
    unsigned int cmd, unsigned long arg) {
    printk(KERN_ALERT "chrdev release!\n");
    return 0;
}

// Kernel interface
static struct file_operations chrdev_fops = {
    .owner      =   THIS_MODULE,
    .ioctl      =   chrdev_ioctl,
    .open       =   chrdev_open,
    .release    =   chrdev_release,
};


#define CHRDEV_NAME "chrdev"
// driver interface
static struct class *chrdev_class = NULL;
static struct device *chrdev_device = NULL;
static dev_t chrdev_devno;
static struct cdev chrdev_cdev;

static int chrdev_probe(struct platform_device *dev) {
    int ret = 0, err = 0;

    printk(KERN_ALERT "chrdev probe!\n");

    // alloc character device number
    ret = alloc_chrdev_region(&chrdev_devno, 0, 1, CHRDEV_NAME);
    if (ret) {
        printk(KERN_ALERT " alloc_chrdev_region failed!\n");
        goto PROBE_ERR;
    }
    printk(KERN_ALERT " major:%d minor:%d\n", MAJOR(chrdev_devno), MINOR(chrdev_devno));

    cdev_init(&chrdev_cdev, &chrdev_fops);
    chrdev_cdev.owner = THIS_MODULE;
    // add a character device
    err = cdev_add(&chrdev_cdev, chrdev_devno, 1);
    if (err) {
        printk(KERN_ALERT " cdev_add failed!\n");
        goto PROBE_ERR;
    }

    // create the device class
    chrdev_class = class_create(THIS_MODULE, CHRDEV_NAME);
    if (IS_ERR(chrdev_class)) {
        printk(KERN_ALERT " class_create failed!\n");
        goto PROBE_ERR;
    }

    // create the device node in /dev
    chrdev_device = device_create(chrdev_class, NULL, chrdev_devno,
        NULL, CHRDEV_NAME);
    if (NULL == chrdev_device) {
        printk(KERN_ALERT " device_create failed!\n");
        goto PROBE_ERR;
    }

    printk(KERN_ALERT " chrdev probe ok!\n");
    return 0;

PROBE_ERR:
    if (err)
        cdev_del(&chrdev_cdev);
    if (ret)
        unregister_chrdev_region(chrdev_devno, 1);
    return -1;
}

static int chrdev_remove (struct platform_device *dev) {
    printk(KERN_ALERT " chrdev remove!\n");

    cdev_del(&chrdev_cdev);
    unregister_chrdev_region(chrdev_devno, 1);

    device_destroy(chrdev_class, chrdev_devno);
    class_destroy(chrdev_class);
    return 0;
}

// platform_device and platform_driver must has a same name!
// or it will not work normally
static struct platform_driver chrdev_platform_driver = {
    .probe  =   chrdev_probe,
    .remove =   chrdev_remove,
    .driver =   {
        .name   =   CHRDEV_NAME,
        .owner  =   THIS_MODULE,
    },
};

static struct platform_device chrdev_platform_device = {
    .name   =   CHRDEV_NAME,
    .id     =   0,
    .dev    =   {
    }
};


static __init int chrdev_init(void) {
    int ret = 0;
    printk(KERN_ALERT "chrdev init!\n");

    ret = platform_device_register(&chrdev_platform_device);
    if (ret) {
        printk(KERN_ALERT " platform_device_register failed!\n");
        return ret;
    }

    ret = platform_driver_register(&chrdev_platform_driver);
    if (ret) {
        printk(KERN_ALERT " platform_driver_register failed!\n");
        return ret;
    }
    printk(KERN_ALERT " chrdev_init ok!\n");
    return ret;
}

static __exit void chrdev_exit(void) {
    printk(KERN_ALERT "chrdev exit!\n");
    platform_driver_unregister(&chrdev_platform_driver);
}

module_init(chrdev_init);
module_exit(chrdev_exit);