2.1 摄像头V4L2驱动框架分析

时间 2020-05-09

标签 2.1 摄像头 v4l2 驱动框架分析繁體版

原文原文链接

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；node

1、V4L2架构linux

1. 字符类驱动数组

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

对于通常的字符类驱动程序，其编写步骤通常分为：app

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：卸载框架

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。以下图所示。ide

--> 上层为核心层（内核已经作好的），在fbmem.c中，主要的做用为：函数

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

--> 硬件相关层（用户须要作的），供核心层的file_operations调用，主要完成：spa

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

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，若是支持，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

因为V4L2驱动程序是一种分层架构，用户只须要完成硬件相关驱动程序便可。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函数的调用结构以下：

vivi_init

-->vivi_create_instance

-->v4l2_device_register // 不是主要, 只是用于初始化一些东西，好比自旋锁、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获得video_device

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

　　　if (vdev->fops->open) //若是有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获得video_device
                                        switch (cmd) { ..... // 根据APP传入的cmd来得到、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);

3、怎么写v4l2驱动？

1. 分配、设置、注册：v4l2_device --》 v4l2_device_register()（辅助做用，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能够经过ioctl来设置（得到）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,每一个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
    这些函数就是建立各个属性，而且放入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, //建立一个属性设置其值，而且放入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;　　　　.........  }