USB摄像头驱动框架分析（五）

1. open:
        uvc_v4l2_open //主要是一些状态的设置
        
应用程序调用ioctl时，就会进入uvc_v4l2_ioctl
 .ioctl = uvc_v4l2_ioctl,
    //把应用程序提供的参数拷贝到内核态，然后调用uvc_v4l2_do_ioctl
    video_usercopy(file, cmd, arg, uvc_v4l2_do_ioctl)
        uvc_v4l2_do_ioctl
            case VIDIOC_QUERYCAP:
                ... //一系列ioctl
            case VIDIOC_G_INPUT:

2. VIDIOC_QUERYCAP    // video->streaming->type 在设备被枚举时分析描述符时初始化
        if (video->streaming->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
            cap->capabilities = V4L2_CAP_VIDEO_CAPTURE
                      | V4L2_CAP_STREAMING;
        else
            cap->capabilities = V4L2_CAP_VIDEO_OUTPUT
                      | V4L2_CAP_STREAMING;
                      
3. VIDIOC_ENUM_FMT // format数组应是在设备被枚举时设置的
        format = &video->streaming->format[fmt->index];
        
4. VIDIOC_G_FMT
        uvc_v4l2_get_format  // USB摄像头支持多种格式fromat, 每种格式下有多种frame(比如分辨率)
                struct uvc_format *format = video->streaming->cur_format;
                struct uvc_frame *frame = video->streaming->cur_frame;
5. VIDIOC_TRY_FMT
        uvc_v4l2_try_format
            /* Check if the hardware supports the requested format. */

            /* Find the closest image size. The distance between image sizes is
             * the size in pixels of the non-overlapping regions between the
             * requested size and the frame-specified size.
             */
6. VIDIOC_S_FMT  // 只是把参数保存起来，还没有发给USB摄像头
        uvc_v4l2_set_format
            uvc_v4l2_try_format
            video->streaming->cur_format = format;
            video->streaming->cur_frame = frame;
7. VIDIOC_REQBUFS
        uvc_alloc_buffers
               for (; nbuffers > 0; --nbuffers) {
                mem = vmalloc_32(nbuffers * bufsize);
                if (mem != NULL)
                    break;
            }
8. VIDIOC_QUERYBUF
        uvc_query_buffer
            __uvc_query_buffer
                memcpy(v4l2_buf, &buf->buf, sizeof *v4l2_buf);  // 复制参数
9. mmap
        uvc_v4l2_mmap
            
10. VIDIOC_QBUF
        uvc_queue_buffer
            list_add_tail(&buf->stream, &queue->mainqueue);
            list_add_tail(&buf->queue, &queue->irqqueue);
            
/*应用程序把buf放入队列后，会调用STREAMON做一些初始化，启动传输，*/
11. VIDIOC_STREAMON
        uvc_video_enable(video, 1)  // 把所设置的参数发给硬件,然后启动摄像头
            /* Commit the streaming parameters. */
            uvc_commit_video
                uvc_set_video_ctrl  /* 设置格式fromat, frame */
                        ret = __uvc_query_ctrl(video->dev /* 哪一个USB设备 */, SET_CUR, 0,
                            video->streaming->intfnum  /* 哪一个接口: VS */,
                            probe ? VS_PROBE_CONTROL : VS_COMMIT_CONTROL, data, size,
                            uvc_timeout_param);
                    
            /* 启动：初始化实时的USB请求块，并分配传输buf. */
            uvc_init_video(video, GFP_KERNEL);
                    uvc_init_video_isoc / uvc_init_video_bulk
                        urb->complete = uvc_video_complete; 
                        /*收到数据后此函数被调用,它又调用video->decode(urb, video, buf); 
                         *最终会调用到=> wake_up(&buf->wait);终止休眠等待*/
                    usb_submit_urb  //初始完后提交urb结构体（USB Request Block） 
                    
/* 调用poll查询数据是否准备就绪，没有的话进入休眠等待 */                     
12. poll
        uvc_v4l2_poll            
            uvc_queue_poll
                poll_wait(file, &buf->wait, wait);  // 休眠等待有数据

/* poll返回之后就表明有可用数据，就从队列中取出buf */
13. VIDIOC_DQBUF
        uvc_dequeue_buffer
            list_del(&buf->stream);

14. VIDIOC_STREAMOFF            
        uvc_video_enable(video, 0);
            usb_kill_urb(urb);
            usb_free_urb(urb);
        
分析设置亮度过程：
ioctl: VIDIOC_S_CTRL
            uvc_ctrl_set
            uvc_ctrl_commit
                __uvc_ctrl_commit(video, 0);
                    uvc_ctrl_commit_entity(video->dev, entity, rollback);
                            ret = uvc_query_ctrl(dev  /* 哪一个USB设备 */, SET_CUR, 
                                    ctrl->entity->id  /* 哪一个unit/terminal */,
                                     dev->intfnum  /* 哪一个接口: VC interface */, 
                                     ctrl->info->selector,
                                     uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT),
                                     ctrl->info->size)