USB摄像头驱动框架分析

1. 分配video_device:video_device_alloc
2. 设置
.fops
.ioctl_ops (里面需要设置11项)
如果要用内核提供的缓冲区操作函数，还需要构造一个videobuf_queue_ops
3. 注册: video_register_device

1.构造一个usb_driver
2.设置
probe:
2.1. 分配video_device:video_device_alloc
2.2. 设置
.fops
.ioctl_ops (里面需要设置11项)
如果要用内核提供的缓冲区操作函数，还需要构造一个videobuf_queue_ops
2.3. 注册: video_register_device
id_table: 表示支持哪些USB设备
3.注册： usb_register

uvcvideo-objs  := uvc_driver.o uvc_queue.o uvc_v4l2.o uvc_video.o uvc_ctrl.o \
uvc_status.o uvc_isight.o
obj-$(CONFIG_USB_VIDEO_CLASS) += uvcvideo.o

result = usb_register(&uvc_driver.driver);

struct uvc_driver uvc_driver = {
.driver = {
.name       = "uvcvideo",
.probe      = uvc_probe,//接上能识别的设备，调用uvc_probe
.disconnect = uvc_disconnect,
.suspend    = uvc_suspend,
.resume     = uvc_resume,
.reset_resume   = uvc_reset_resume,
.id_table   = uvc_ids,
.supports_autosuspend = 1,
},
};

uvc_probe
uvc_register_video//注册
vdev = video_device_alloc();//分配
vdev->fops = &uvc_fops;//设置
const struct v4l2_file_operations uvc_fops = {
.owner      = THIS_MODULE,
.open     = uvc_v4l2_open,
.release  = uvc_v4l2_release,
.ioctl        = uvc_v4l2_ioctl,
.read     = uvc_v4l2_read,
.mmap     = uvc_v4l2_mmap,
.poll     = uvc_v4l2_poll };
video_register_device//注册

CT:Camera Terminal          IT:Input  Terminal
SU:Select Unit                     PU:Process Unit
OT:Out Terminal

1.open:
uvc_v4l2_open

const struct v4l2_file_operations uvc_fops = {
.owner      = THIS_MODULE,
.open       = uvc_v4l2_open,
.release    = uvc_v4l2_release,
.ioctl      = uvc_v4l2_ioctl,
.read       = uvc_v4l2_read,
.mmap       = uvc_v4l2_mmap,
.poll       = uvc_v4l2_poll,
};

2. ioctl:
uvc_v4l2_ioctl
return video_usercopy(file, cmd, arg, uvc_v4l2_do_ioctl);
//将应用程度提供的参数拷贝到内核，然后调用uvc_v4l2_do_ioctl
uvc_v4l2_do_ioctl
/* Query capabilities */
VIDIOC_QUERYCAP//查询驱动功能
if (video->streaming->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)//*video->streaming->type 应该是在usb摄像头设备被枚举时分析描述符时设置的
cap->capabilities = V4L2_CAP_VIDEO_CAPTURE
| V4L2_CAP_STREAMING;
else
cap->capabilities = V4L2_CAP_VIDEO_OUTPUT
| V4L2_CAP_STREAMING;

3. VIDIOC_ENUM_FMT //获取当前驱动支持的视频格式
format = &video->streaming->format[fmt->index];// format数组应是在设备被枚举时设置的

4. VIDIOC_G_FMT //读取当前驱动的视频捕获格式
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;//当前的格式
struct uvc_frame *frame = video->streaming->cur_frame;//当前的帧

5. VIDIOC_TRY_FMT //验证当前驱动的显示格式
uvc_v4l2_try_format
/* Check if the hardware supports the requested format. */
/*检查硬件是否支持请求的格式*/
/* 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 */
/*找到最接近的图像大小。 图像尺寸之间的距离是大小以像素之间的非重叠区域为单位请求的大小和帧指定的大小。*/

6. VIDIOC_S_FMT  // 设置当前驱动的视频捕获格式，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 //申请缓冲区
unsigned int bufsize =
video->streaming->ctrl.dwMaxVideoFrameSize;//缓冲区大小
uvc_alloc_buffers
for (; nbuffers > 0; --nbuffers) {
mem = vmalloc_32(nbuffers * bufsize);//分配nbuffers个缓冲区
if (mem != NULL)
break;
}

8. VIDIOC_QUERYBUF //查询缓冲区

uvc_query_buffer
__uvc_query_buffer
memcpy(v4l2_buf, &buf->buf, sizeof *v4l2_buf);  // 复制参数

9. mmap //映射缓冲区
uvc_v4l2_mmap

10. VIDIOC_QBUF//把buffer放入缓存队列，当有数据时将buffer从队列中取出
uvc_queue_buffer
list_add_tail(&buf->stream, &queue->mainqueue);
list_add_tail(&buf->queue, &queue->irqqueue);

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 //把参数提交给硬件
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：Initialize isochronous/bulk URBs and allocate transfer buffers. */
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); ==> uvc_video_decode_isoc/uvc_video_encode_bulk => uvc_queue_next_buffer => wake_up(&buf->wait);)

usb_submit_urb

12. poll //查看buffer是否已有数据
uvc_v4l2_poll
uvc_queue_poll
poll_wait(file, &buf->wait, wait);  // 休眠等待有数据

13. VIDIOC_DQBUF //将数据从队列中取出
uvc_dequeue_buffer
list_del(&buf->stream);

14. VIDIOC_STREAMOFF //关闭传输
uvc_video_enable(video, 0);
usb_kill_urb(urb);
usb_free_urb(urb);

ioctl: VIDIOC_S_CTRL （uvc_v4l2.c）
uvc_ctrl_set  //设置
uvc_ctrl_commit  //提交
__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);

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);

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);