2.1 摄像头V4L2驱动框架分析

点点圈 提交于 2020-12-07 05:43:01

学习目标:学习V4L2(V4L2:vidio for linux version 2)摄像头驱动框架,分析vivi.c(虚拟视频硬件相关)驱动源码程序,总结V4L2硬件相关的驱动的步骤;

 一、V4L2架构

1. 字符类驱动

V4L2(V4L2:vidio for linux version 2)摄像头驱动属于字符类驱动,

对于一般的字符类驱动程序,其编写步骤一般分为:

1)构造一个file_operations: 编写open=drv_open .read=drv_read
2)注册设备,告诉内核:register_chrdev(主设备号,名字,&file_operations)
3)入口函数:调用register_chrdev
4)出口函数:卸载

对于复杂的字符类驱动程序,其程序是一种分层结构。例如LCD驱动程序。如下图所示。

--> 上层为核心层(内核已经做好的),在fbmem.c中 ,主要的作用为:

1)构造file_operations(open read write 函数);2)注册;3)入口、出口。

--> 硬件相关层(用户需要做的),供核心层的file_operations调用,主要完成:

1) 分配一个fb_info 结构体;2) 设置fb_info 结构体等;3) 注册;4) 硬件相关的操作。 

2. V4L2驱动架构

由以上字符类设备驱动架构可知,摄像头驱动也是分层结构的。

其中,ucv_driver.c中,定义了uvc_driver结构体,根据ucv_ids查找匹配的设备,如果支持,则会进入probe函数

 1 struct uvc_driver uvc_driver = {
 2     .driver = {
 3         .name        = "uvcvideo",
 4         .probe        = uvc_probe,
 5         .disconnect    = uvc_disconnect,
 6         .suspend    = uvc_suspend,
 7         .resume        = uvc_resume,
 8         .reset_resume    = uvc_reset_resume,
 9         .id_table    = uvc_ids,
10         .supports_autosuspend = 1,
11     },
12 };

二. vivi.c虚拟视频驱动程序架构

由于V4L2驱动程序是一种分层架构,用户只需要完成硬件相关驱动程序即可。这里主要以vivi虚拟视频驱动程序为例分析源码的调用过程和框架。

1.  进入入口的vivi_init(void)函数:

  1 static int __init vivi_create_instance(int inst)
  2 {
  3     struct vivi_dev *dev;
  4     struct video_device *vfd; //video_device结构体定义
  5     struct v4l2_ctrl_handler *hdl;
  6     struct vb2_queue *q;
  7     int ret;
  8 
  9     dev = kzalloc(sizeof(*dev), GFP_KERNEL);
 10     if (!dev)
 11         return -ENOMEM;
 12 
 13     snprintf(dev->v4l2_dev.name, sizeof(dev->v4l2_dev.name),
 14             "%s-%03d", VIVI_MODULE_NAME, inst);
 15     ret = v4l2_device_register(NULL, &dev->v4l2_dev);
 16     if (ret)
 17         goto free_dev;
 18    //摄像头相关属性设置
 19     dev->fmt = &formats[0];
 20     dev->width = 640;
 21     dev->height = 480;
 22     hdl = &dev->ctrl_handler;
 23     v4l2_ctrl_handler_init(hdl, 11);
 24     dev->volume = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
 25             V4L2_CID_AUDIO_VOLUME, 0, 255, 1, 200);
 26     dev->brightness = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
 27             V4L2_CID_BRIGHTNESS, 0, 255, 1, 127);
 28     dev->contrast = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
 29             V4L2_CID_CONTRAST, 0, 255, 1, 16);
 30     dev->saturation = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
 31             V4L2_CID_SATURATION, 0, 255, 1, 127);
 32     dev->hue = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
 33             V4L2_CID_HUE, -128, 127, 1, 0);
 34     dev->autogain = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
 35             V4L2_CID_AUTOGAIN, 0, 1, 1, 1);
 36     dev->gain = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
 37             V4L2_CID_GAIN, 0, 255, 1, 100);
55 /* initialize queue */ 56 q = &dev->vb_vidq; 57 memset(q, 0, sizeof(dev->vb_vidq)); 58 q->type = V4L2_BUF_TYPE_VIDEO_CAPTURE; 59 q->io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ; 60 q->drv_priv = dev; 61 q->buf_struct_size = sizeof(struct vivi_buffer); 62 q->ops = &vivi_video_qops; 63 q->mem_ops = &vb2_vmalloc_memops; 64 65 vb2_queue_init(q); 66 67 mutex_init(&dev->mutex); 68 69 /* init video dma queues */ 70 INIT_LIST_HEAD(&dev->vidq.active); 71 init_waitqueue_head(&dev->vidq.wq); 72 73 ret = -ENOMEM;
     //分配video_device结构体
74 vfd = video_device_alloc(); 75 if (!vfd) 76 goto unreg_dev; 77  //设置 78 *vfd = vivi_template;
  /******************************************************************
    其中,以赋值的方式进行设置vfd,进入vivi_template:
      static struct video_device vivi_template = {
       .name  = "vivi",
       .fops          = &vivi_fops,
       .ioctl_ops    = &vivi_ioctl_ops,
       .release     = video_device_release,
       .tvnorms              = V4L2_STD_525_60,
       .current_norm         = V4L2_STD_NTSC_M,
      };
  *******************************************************************//
 79     vfd->debug = debug;
 80     vfd->v4l2_dev = &dev->v4l2_dev;
 81     set_bit(V4L2_FL_USE_FH_PRIO, &vfd->flags);
 82 
 83     /*
 84      * Provide a mutex to v4l2 core. It will be used to protect
 85      * all fops and v4l2 ioctls.
 86      */
 87     vfd->lock = &dev->mutex;
 88     //注册
 89     ret = video_register_device(vfd, VFL_TYPE_GRABBER, video_nr);
93 video_set_drvdata(vfd, dev); 94 95 /* Now that everything is fine, let's add it to device list */ 96 list_add_tail(&dev->vivi_devlist, &vivi_devlist); 97 101 dev->vfd = vfd; 102 v4l2_info(&dev->v4l2_dev, "V4L2 device registered as %s\n", 103 video_device_node_name(vfd)); 104 return 0;
107 video_device_release(vfd);110 v4l2_device_unregister(&dev->v4l2_dev);114 }

 vivi_init函数的调用结构如下:

vivi_init

   -->vivi_create_instance

        -->v4l2_device_register   // 不是主要, 只是用于初始化一些东西,比如自旋锁、引用计数

              vfd = video_device_alloc(); //分配video_device结构体

             1.  *vfd = vivi_template; // 设置

              .fops           = &vivi_fops,
              .ioctl_ops    = &vivi_ioctl_ops,
              .release      = video_device_release,

     2.  vfd->v4l2_dev = &dev->v4l2_dev;

     3.  设置"ctrl属性"(用于APP的ioctl):
               v4l2_ctrl_handler_init(hdl, 11);
               dev->volume = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
                V4L2_CID_AUDIO_VOLUME, 0, 255, 1, 200);
               dev->brightness = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
                V4L2_CID_BRIGHTNESS, 0, 255, 1, 127);
               dev->contrast = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
                V4L2_CID_CONTRAST, 0, 255, 1, 16);      

    4. video_register_device(vfd, VFL_TYPE_GRABBER, video_nr);  //注册

       --> __video_register_device(vdev, type, nr, 1, vdev->fops->owner);

         -->vdev->cdev = cdev_alloc();  (v4l2.dev.c程序中)

           vdev->cdev->ops = &v4l2_fops;

           cdev_add(vdev->cdev, MKDEV(VIDEO_MAJOR, vdev->minor), 1);

2. vivi.c的open,read,write,ioctl过程

1 static const struct v4l2_file_operations vivi_fops = {
2     .owner        = THIS_MODULE,
3     .open           = v4l2_fh_open,
4     .release        = vivi_close,
5     .read           = vivi_read,
6     .poll         = vivi_poll,
7     .unlocked_ioctl = video_ioctl2, /* V4L2 ioctl handler */
8     .mmap           = vivi_mmap,
9 };

1)open

app:     open("/dev/video0",....)向下层调用
-------------------------------------------------------------------
drv:     v4l2_fops.v4l2_open
           vdev = video_devdata(filp);  // 根据次设备号从数组中得到video_device

       return video_device[iminor(file->f_path.dentry->d_inode)];

   if (vdev->fops->open)     //如果有open函数
      if (video_is_registered(vdev))
        ret = vdev->fops->open(filp);//调用open 函数
          调用vivi.c 里的v4l2_fh_open函数

2)read

app:     read("/dev/video0",....)向下层调用
-------------------------------------------------------------------

drv:    v4l2_fops.v4l2_read
            struct video_device *vdev = video_devdata(filp);
            if (video_is_registered(vdev))
      ret = vdev->fops->read(filp, buf, sz, off);

       调用vivi.c 里的vivi_read

3)ioctl
app:   ioctl 
----------------------------------------------------
drv:   v4l2_fops.unlocked_ioctl => v4l2_ioctl
                struct video_device *vdev = video_devdata(filp);
             if (video_is_registered(vdev))
       ret = vdev->fops->unlocked_ioctl(filp, cmd, arg);
                       调用vivi.c 里的video_ioctl2
                                video_usercopy(file, cmd, arg, __video_do_ioctl); //从用户空间把用户的命令cmd复制进来,调用__video_do_ioctl
                                    __video_do_ioctl
                                        struct video_device *vfd = video_devdata(file); // 根据次设备号从数组中得到video_device
                                        switch (cmd) { .....     // 根据APP传入的cmd来获得、设置"某些属性"
 
--->>(例程分析:2.3节)
v4l2_ctrl_handler的使用过程:
      .......
     case VIDIOC_QUERYCTRL:
     {
      struct v4l2_queryctrl *p = arg;
      if (vfh && vfh->ctrl_handler)
          ret = v4l2_queryctrl(vfh->ctrl_handler, p);
      else if (vfd->ctrl_handler)  // 在video_register_device设置 vivi_create_instance-->hdl = &dev->ctrl_handler;    v4l2_ctrl_handler_init(hdl, 11);
         ret = v4l2_queryctrl(vfd->ctrl_handler, p);  // 根据ID在ctrl_handler里找到v4l2_ctrl,返回它的值
-------->>
 1 hdl = &dev->ctrl_handler;
 2     v4l2_ctrl_handler_init(hdl, 11);
 3     dev->volume = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
 4             V4L2_CID_AUDIO_VOLUME, 0, 255, 1, 200);
 5     dev->brightness = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
 6             V4L2_CID_BRIGHTNESS, 0, 255, 1, 127);
 7     dev->contrast = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
 8             V4L2_CID_CONTRAST, 0, 255, 1, 16);
 9     dev->saturation = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
10             V4L2_CID_SATURATION, 0, 255, 1, 127);
11     dev->hue = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
12             V4L2_CID_HUE, -128, 127, 1, 0);
13     dev->autogain = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
14             V4L2_CID_AUTOGAIN, 0, 1, 1, 1);
15     dev->gain = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
16             V4L2_CID_GAIN, 0, 255, 1, 100);

三、怎么写v4l2驱动?

1. 分配、设置、注册:v4l2_device --》 v4l2_device_register()(辅助作用,提供自旋锁、引用计数等功能)

2. 分配一个video_device:video_device_alloc()

3. 设置

1)vfd->v4l2_dev  

2)  .fops             设置vfd的fops 里的open、read、write 被上层调用
  .ioctl_ops      设置属性被上层调用    

3)注册:video_register_device()

4. 接下来,应用层App可以通过ioctl来设置(获得)亮度等某些属性,在驱动程序里,谁来接收、存储、设置到硬件(提供这些信息)?

在驱动程序中抽象出来一个结构体v4l2_ctrl,每个Ctrl对应其中的一项(音量、亮度等等);

 v4l2_ctrl_handler来管理他们,在vivi.c的vivi_create_instance函数中:

  1.初始化
    v4l2_ctrl_handler_init
  2.设置
    v4l2_ctrl_new_std
    v4l2_ctrl_new_custom
    这些函数就是创建各个属性,并且放入v4l2_ctrl_handler的链表
  3.跟vdev关联
    dev->v4l2_dev.ctrl_handler = hdl;

 1 static int __init vivi_create_instance(int inst)
 2 {
 3     struct vivi_dev *dev;
 4     struct video_device *vfd;
 5     struct v4l2_ctrl_handler *hdl; //定义v4l2_ctrl_handler结构体
 6     struct vb2_queue *q;
 7     int ret;
 8 
 9     dev = kzalloc(sizeof(*dev), GFP_KERNEL);
10     if (!dev)
11         return -ENOMEM;
12 
13     snprintf(dev->v4l2_dev.name, sizeof(dev->v4l2_dev.name),
14             "%s-%03d", VIVI_MODULE_NAME, inst);
15     ret = v4l2_device_register(NULL, &dev->v4l2_dev);
16     if (ret)
17         goto free_dev;
18 
19     dev->fmt = &formats[0];  
20     dev->width = 640;
21     dev->height = 480;
22     hdl = &dev->ctrl_handler;
23     v4l2_ctrl_handler_init(hdl, 11); //初始化
24     dev->volume = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops, //创建一个属性设置其值,并且放入v4l2_ctrl_handler的链表
25             V4L2_CID_AUDIO_VOLUME, 0, 255, 1, 200);
26     dev->brightness = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
27             V4L2_CID_BRIGHTNESS, 0, 255, 1, 127);
28     dev->contrast = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
29             V4L2_CID_CONTRAST, 0, 255, 1, 16);
30     dev->saturation = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
31             V4L2_CID_SATURATION, 0, 255, 1, 127);
32     dev->hue = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
33             V4L2_CID_HUE, -128, 127, 1, 0);
34     dev->autogain = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
35             V4L2_CID_AUTOGAIN, 0, 1, 1, 1);
36     dev->gain = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
37             V4L2_CID_GAIN, 0, 255, 1, 100);
38     dev->button = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_button, NULL);
39     dev->int32 = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_int32, NULL);
40     dev->int64 = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_int64, NULL);
41     dev->boolean = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_boolean, NULL);
42     dev->menu = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_menu, NULL);

45 dev->v4l2_dev.ctrl_handler = hdl;
    .........
}

 

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