v4l2,camera笔记

开始学习v4l2中camera的架构

    app调用v4l2框架，然后v4l2框架再调用具体的驱动

     如：在app:open----->v4l2:open------->driver:open

   v4l2提供的是一个通用的框架，然后驱动去实现具体的内容。

   问题：那么v4l2是怎么调用driver的呢？

           这个我们看看相关代码就很清楚了。

//drivers/media/video/v4l2-dev.c

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1. static int v4l2_open(struct inode *inode, struct file *filp)  
2. {  
3.     printk("<6>\nsong:**************v4l2_open************\n");  
4.     struct video_device *vdev;  
5.     int ret = 0;  
6.     /* Check if the video device is available */  
7.     mutex_lock(&videodev_lock);  
8.     //这里就是从我们的在驱动中注册的video_device->cdev得到video_device.  
9.     vdev = video_devdata(filp);  
10.    /* return ENODEV if the video device has been removed  
11.        already or if it is not registered anymore. */  
12.     if (vdev == NULL || !video_is_registered(vdev)) {  
13.         mutex_unlock(&videodev_lock);  
14.         return -ENODEV;  
15.     }  
16.     /* and increase the device refcount */  
17.     video_get(vdev);  
18.     mutex_unlock(&videodev_lock);  
19.         //调用在驱动注册的open方法  
20.     if (vdev->fops->open)  
21.         ret = vdev->fops->open(filp);  
22.   
23.     /* decrease the refcount in case of an error */  
24.     if (ret)  
25.         video_put(vdev);  
26.     return ret;  
27. }  

static int v4l2_open(struct inode *inode, struct file *filp){    printk("<6>\nsong:**************v4l2_open************\n");    struct video_device *vdev;    int ret = 0;    /* Check if the video device is available */    mutex_lock(&videodev_lock);    //这里就是从我们的在驱动中注册的video_device->cdev得到video_device.    vdev = video_devdata(filp);   /* return ENODEV if the video device has been removed       already or if it is not registered anymore. */    if (vdev == NULL || !video_is_registered(vdev)) {        mutex_unlock(&videodev_lock);        return -ENODEV;    }    /* and increase the device refcount */    video_get(vdev);    mutex_unlock(&videodev_lock);        //调用在驱动注册的open方法    if (vdev->fops->open)        ret = vdev->fops->open(filp);    /* decrease the refcount in case of an error */    if (ret)        video_put(vdev);    return ret;}

  其它操作和open操作是一样的。

下面来看具体的驱动代码：

1.首先dcam_init()

在初始化的时候要注册一个platform driver：

platform_driver_register(&dcam_driver) 

然后进行相关初始化：create_instance(i)

相关代码：

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1. int __init dcam_v4l2_init(void)  
2. {  
3.     int ret = 0, i;  
4.       
5.     if(platform_driver_register(&dcam_driver) != 0) {  
6.         printk("platform device register Failed \n");  
7.         return -1;  
8.     }  
9.        // 省略  
10.           
11.         ret = create_instance(i);      
12.          
13.   
14.         // 省略  
15.   
16. return ret;}  
17.   
18. static struct platform_driver dcam_driver = {  
19.     .probe    = dcam_probe,  
20.     .remove   = dcam_remove,  
21.     .driver   = {  
22.         .owner = THIS_MODULE,  
23.         .name = "XXXXX_dcam",  
24.     },  
25. };  
26.   
27. static int __init create_instance(int inst)  
28. {  
29.     struct dcam_dev *dev;  
30.     struct video_device *vfd;  
31.     int ret, i;  
32.   
33.     dev = kzalloc(sizeof(*dev), GFP_KERNEL);  
34.     if (!dev)  
35.         return -ENOMEM;  
36.   
37.     snprintf(dev->v4l2_dev.name, sizeof(dev->v4l2_dev.name),  
38.             "%s-%03d", DCAM_MODULE_NAME, inst);  
39.     ret = v4l2_device_register(NULL, &dev->v4l2_dev);  
40. //初始化v4l2_device  
41.     if (ret)  
42.         goto free_dev;  
43.   
44.     /* init video dma queues */  
45.     INIT_LIST_HEAD(&dev->vidq.active);  
46.     init_waitqueue_head(&dev->vidq.wq);  
47.   
48.     /* initialize locks */  
49.     spin_lock_init(&dev->slock);  
50.     mutex_init(&dev->mutex);  
51.   
52.     ret = -ENOMEM;  
53. //为video_device分配内存  
54.     vfd = video_device_alloc();  
55.     if (!vfd)  
56.         goto unreg_dev;  
57. //为vfd赋值  
58.     *vfd = dcam_template;  
59.     vfd->debug = debug;  
60. //注册video_device，主要作用是注册cdev，具体看实现，这个函数很重要  
61.     ret = video_register_device(vfd, VFL_TYPE_GRABBER, video_nr);  
62.     if (ret < 0)  
63.         goto rel_vdev;  
64.   
65.     video_set_drvdata(vfd, dev);  
66.   
67.     /* Set all controls to their default value. */  
68.     for (i = 0; i < ARRAY_SIZE(dcam_qctrl); i++)  
69.         dev->qctl_regs[i] = dcam_qctrl[i].default_value;  
70.   
71.     /* Now that everything is fine, let's add it to device list */  
72.     list_add_tail(&dev->dcam_devlist, &dcam_devlist);  
73.   
74.     snprintf(vfd->name, sizeof(vfd->name), "%s (%i)",  
75.             dcam_template.name, vfd->num);  
76.   
77.     if (video_nr >= 0)  
78.         video_nr++;  
79.   
80.     dev->vfd = vfd;  
81.     v4l2_info(&dev->v4l2_dev, "V4L2 device registered as /dev/video%d\n",  
82.             vfd->num);  
83.     return 0;  
84.   
85. rel_vdev:  
86.     video_device_release(vfd);  
87. unreg_dev:  
88.     v4l2_device_unregister(&dev->v4l2_dev);  
89. free_dev:  
90.     kfree(dev);  
91.     return ret;  
92. }  
93.   
94. static struct video_device dcam_template = {  
95.     .name        = "dcam",  
96.     .fops           = &dcam_fops,  
97.     .ioctl_ops     = &dcam_ioctl_ops,  
98.     .minor        = -1,  
99.     .release    = video_device_release,  
100.   
101.     .tvnorms              = V4L2_STD_525_60,  
102.     .current_norm         = V4L2_STD_NTSC_M,  
103. };  
104.   
105.   
106. //现在分析probe函数  
107. //主要作用是注册一个miscdevice  
108. int dcam_probe(struct platform_device *pdev)  
109. {  
110.     int ret;  
111.     printk(KERN_ALERT"dcam_probe called\n");  
112.   
113.     ret = misc_register(&dcam_v4l2_dev);//这个可以去查看相关的注册过程  
114.     if (ret) {  
115.         printk (KERN_ERR "cannot register miscdev on minor=%d (%d)\n",  
116.                 DCAM_MINOR, ret);  
117.         return ret;  
118.     }  
119.   
120.     lock = (struct mutex *)kmalloc(sizeof(struct mutex), GFP_KERNEL);  
121.     if (lock == NULL)  
122.         return -1;  
123.   
124.     mutex_init(lock);      
125.   
126.     printk(KERN_ALERT "dcam_probe Success.\n");  
127.   
128.     return 0;  
129. }  
130. static struct miscdevice dcam_v4l2_dev = {  
131.     .minor   = DCAM_MINOR,  
132.     .name   = "sc8800g_dcam",  
133.     .fops   = &dcam_fops,  
134. };  

int __init dcam_v4l2_init(void){    int ret = 0, i;        if(platform_driver_register(&dcam_driver) != 0) {        printk("platform device register Failed \n");        return -1;    }       // 省略                ret = create_instance(i);                   // 省略return ret;}static struct platform_driver dcam_driver = {    .probe    = dcam_probe,    .remove   = dcam_remove,    .driver   = {        .owner = THIS_MODULE,        .name = "XXXXX_dcam",    },};static int __init create_instance(int inst){    struct dcam_dev *dev;    struct video_device *vfd;    int ret, i;    dev = kzalloc(sizeof(*dev), GFP_KERNEL);    if (!dev)        return -ENOMEM;    snprintf(dev->v4l2_dev.name, sizeof(dev->v4l2_dev.name),            "%s-%03d", DCAM_MODULE_NAME, inst);    ret = v4l2_device_register(NULL, &dev->v4l2_dev);//初始化v4l2_device    if (ret)        goto free_dev;    /* init video dma queues */    INIT_LIST_HEAD(&dev->vidq.active);    init_waitqueue_head(&dev->vidq.wq);    /* initialize locks */    spin_lock_init(&dev->slock);    mutex_init(&dev->mutex);    ret = -ENOMEM;//为video_device分配内存    vfd = video_device_alloc();    if (!vfd)        goto unreg_dev;//为vfd赋值    *vfd = dcam_template;    vfd->debug = debug;//注册video_device，主要作用是注册cdev，具体看实现，这个函数很重要    ret = video_register_device(vfd, VFL_TYPE_GRABBER, video_nr);    if (ret < 0)        goto rel_vdev;    video_set_drvdata(vfd, dev);    /* Set all controls to their default value. */    for (i = 0; i < ARRAY_SIZE(dcam_qctrl); i++)        dev->qctl_regs[i] = dcam_qctrl[i].default_value;    /* Now that everything is fine, let's add it to device list */    list_add_tail(&dev->dcam_devlist, &dcam_devlist);    snprintf(vfd->name, sizeof(vfd->name), "%s (%i)",            dcam_template.name, vfd->num);    if (video_nr >= 0)        video_nr++;    dev->vfd = vfd;    v4l2_info(&dev->v4l2_dev, "V4L2 device registered as /dev/video%d\n",            vfd->num);    return 0;rel_vdev:    video_device_release(vfd);unreg_dev:    v4l2_device_unregister(&dev->v4l2_dev);free_dev:    kfree(dev);    return ret;}static struct video_device dcam_template = {    .name        = "dcam",    .fops           = &dcam_fops,    .ioctl_ops     = &dcam_ioctl_ops,    .minor        = -1,    .release    = video_device_release,    .tvnorms              = V4L2_STD_525_60,    .current_norm         = V4L2_STD_NTSC_M,};//现在分析probe函数//主要作用是注册一个miscdeviceint dcam_probe(struct platform_device *pdev){    int ret;    printk(KERN_ALERT"dcam_probe called\n");    ret = misc_register(&dcam_v4l2_dev);//这个可以去查看相关的注册过程    if (ret) {        printk (KERN_ERR "cannot register miscdev on minor=%d (%d)\n",                DCAM_MINOR, ret);        return ret;    }    lock = (struct mutex *)kmalloc(sizeof(struct mutex), GFP_KERNEL);    if (lock == NULL)        return -1;    mutex_init(lock);        printk(KERN_ALERT "dcam_probe Success.\n");    return 0;}static struct miscdevice dcam_v4l2_dev = {    .minor   = DCAM_MINOR,    .name   = "sc8800g_dcam",    .fops   = &dcam_fops,};

这样基本上一个设备就可以正常工作了。