UVC（1）-v4l2框架分析
此节是韦东山第三期学习资料
当插入一个网上买的UVC时，内核UVC驱动会打印出下面的Log信息出来
对应的UVC驱动位于：/drivers/media/usb/uvc
当插入的UVC与uvc_ids匹配了，就会调用uvc_probe函数枚举设备
struct uvc_driver uvc_driver = { .driver = { .name = "uvcvideo", .probe = uvc_probe, .disconnect = uvc_disconnect, .suspend = uvc_suspend, .resume = uvc_resume, .reset_resume = uvc_reset_resume, .id_table = uvc_ids, .supports_autosuspend = 1, }, };
在uvc_probe函数中，
uvc_probe ->v4l2_device_register ->uvc_register_chains ->uvc_register_terms ->uuv_register_video ->video_register_device // 注册video_device，video_device使用cdev方式注册，cdev_ops = v4l2_fops
虚拟视频驱动vivid.c分析：
1、分配video_device
2、设置video_device结构体
3、注册video_device结构体
代码位置：linux/drivers/platform/vivid
vivid-core.c
static const struct v4l2_file_operations vivid_fops = { .owner = THIS_MODULE, .open = v4l2_fh_open, .release = vivid_fop_release, .read = vb2_fop_read, .write = vb2_fop_write, .poll = vb2_fop_poll, .unlocked_ioctl = video_ioctl2, .mmap = vb2_fop_mmap, }; static const struct v4l2_file_operations vivid_radio_fops = { .owner = THIS_MODULE, .open = v4l2_fh_open, .release = vivid_fop_release, .read = vivid_radio_read, .write = vivid_radio_write, .poll = vivid_radio_poll, .unlocked_ioctl = video_ioctl2, }; static const struct v4l2_ioctl_ops vivid_ioctl_ops = { .vidioc_querycap = vidioc_querycap, .vidioc_enum_fmt_vid_cap = vidioc_enum_fmt_vid, .vidioc_g_fmt_vid_cap = vidioc_g_fmt_vid_cap, .vidioc_try_fmt_vid_cap = vidioc_try_fmt_vid_cap, .vidioc_s_fmt_vid_cap = vidioc_s_fmt_vid_cap, .vidioc_enum_fmt_vid_cap_mplane = vidioc_enum_fmt_vid_mplane, .vidioc_g_fmt_vid_cap_mplane = vidioc_g_fmt_vid_cap_mplane, .vidioc_try_fmt_vid_cap_mplane = vidioc_try_fmt_vid_cap_mplane, .vidioc_s_fmt_vid_cap_mplane = vidioc_s_fmt_vid_cap_mplane, .vidioc_enum_fmt_vid_out = vidioc_enum_fmt_vid, .vidioc_g_fmt_vid_out = vidioc_g_fmt_vid_out, .vidioc_try_fmt_vid_out = vidioc_try_fmt_vid_out, .vidioc_s_fmt_vid_out = vidioc_s_fmt_vid_out, .vidioc_enum_fmt_vid_out_mplane = vidioc_enum_fmt_vid_mplane, .vidioc_g_fmt_vid_out_mplane = vidioc_g_fmt_vid_out_mplane, .vidioc_try_fmt_vid_out_mplane = vidioc_try_fmt_vid_out_mplane, .vidioc_s_fmt_vid_out_mplane = vidioc_s_fmt_vid_out_mplane, .vidioc_g_selection = vidioc_g_selection, .vidioc_s_selection = vidioc_s_selection, .vidioc_cropcap = vidioc_cropcap, .vidioc_g_fmt_vbi_cap = vidioc_g_fmt_vbi_cap, .vidioc_try_fmt_vbi_cap = vidioc_g_fmt_vbi_cap, .vidioc_s_fmt_vbi_cap = vidioc_s_fmt_vbi_cap, .vidioc_g_fmt_sliced_vbi_cap = vidioc_g_fmt_sliced_vbi_cap, .vidioc_try_fmt_sliced_vbi_cap = vidioc_try_fmt_sliced_vbi_cap, .vidioc_s_fmt_sliced_vbi_cap = vidioc_s_fmt_sliced_vbi_cap, .vidioc_g_sliced_vbi_cap = vidioc_g_sliced_vbi_cap, .vidioc_g_fmt_vbi_out = vidioc_g_fmt_vbi_out, .vidioc_try_fmt_vbi_out = vidioc_g_fmt_vbi_out, .vidioc_s_fmt_vbi_out = vidioc_s_fmt_vbi_out, .vidioc_g_fmt_sliced_vbi_out = vidioc_g_fmt_sliced_vbi_out, .vidioc_try_fmt_sliced_vbi_out = vidioc_try_fmt_sliced_vbi_out, .vidioc_s_fmt_sliced_vbi_out = vidioc_s_fmt_sliced_vbi_out, .vidioc_enum_fmt_sdr_cap = vidioc_enum_fmt_sdr_cap, .vidioc_g_fmt_sdr_cap = vidioc_g_fmt_sdr_cap, .vidioc_try_fmt_sdr_cap = vidioc_g_fmt_sdr_cap, .vidioc_s_fmt_sdr_cap = vidioc_g_fmt_sdr_cap, .vidioc_overlay = vidioc_overlay, .vidioc_enum_framesizes = vidioc_enum_framesizes, .vidioc_enum_frameintervals = vidioc_enum_frameintervals, .vidioc_g_parm = vidioc_g_parm, .vidioc_s_parm = vidioc_s_parm, .vidioc_enum_fmt_vid_overlay = vidioc_enum_fmt_vid_overlay, .vidioc_g_fmt_vid_overlay = vidioc_g_fmt_vid_overlay, .vidioc_try_fmt_vid_overlay = vidioc_try_fmt_vid_overlay, .vidioc_s_fmt_vid_overlay = vidioc_s_fmt_vid_overlay, .vidioc_g_fmt_vid_out_overlay = vidioc_g_fmt_vid_out_overlay, .vidioc_try_fmt_vid_out_overlay = vidioc_try_fmt_vid_out_overlay, .vidioc_s_fmt_vid_out_overlay = vidioc_s_fmt_vid_out_overlay, .vidioc_g_fbuf = vidioc_g_fbuf, .vidioc_s_fbuf = vidioc_s_fbuf, .vidioc_reqbufs = vb2_ioctl_reqbufs, .vidioc_create_bufs = vb2_ioctl_create_bufs, .vidioc_prepare_buf = vb2_ioctl_prepare_buf, .vidioc_querybuf = vb2_ioctl_querybuf, .vidioc_qbuf = vb2_ioctl_qbuf, .vidioc_dqbuf = vb2_ioctl_dqbuf, .vidioc_expbuf = vb2_ioctl_expbuf, .vidioc_streamon = vb2_ioctl_streamon, .vidioc_streamoff = vb2_ioctl_streamoff, .vidioc_enum_input = vidioc_enum_input, .vidioc_g_input = vidioc_g_input, .vidioc_s_input = vidioc_s_input, .vidioc_s_audio = vidioc_s_audio, .vidioc_g_audio = vidioc_g_audio, .vidioc_enumaudio = vidioc_enumaudio, .vidioc_s_frequency = vidioc_s_frequency, .vidioc_g_frequency = vidioc_g_frequency, .vidioc_s_tuner = vidioc_s_tuner, .vidioc_g_tuner = vidioc_g_tuner, .vidioc_s_modulator = vidioc_s_modulator, .vidioc_g_modulator = vidioc_g_modulator, .vidioc_s_hw_freq_seek = vidioc_s_hw_freq_seek, .vidioc_enum_freq_bands = vidioc_enum_freq_bands, .vidioc_enum_output = vidioc_enum_output, .vidioc_g_output = vidioc_g_output, .vidioc_s_output = vidioc_s_output, .vidioc_s_audout = vidioc_s_audout, .vidioc_g_audout = vidioc_g_audout, .vidioc_enumaudout = vidioc_enumaudout, .vidioc_querystd = vidioc_querystd, .vidioc_g_std = vidioc_g_std, .vidioc_s_std = vidioc_s_std, .vidioc_s_dv_timings = vidioc_s_dv_timings, .vidioc_g_dv_timings = vidioc_g_dv_timings, .vidioc_query_dv_timings = vidioc_query_dv_timings, .vidioc_enum_dv_timings = vidioc_enum_dv_timings, .vidioc_dv_timings_cap = vidioc_dv_timings_cap, .vidioc_g_edid = vidioc_g_edid, .vidioc_s_edid = vidioc_s_edid, .vidioc_log_status = v4l2_ctrl_log_status, .vidioc_subscribe_event = vidioc_subscribe_event, .vidioc_unsubscribe_event = v4l2_event_unsubscribe, };
vivid_init ->vivid_probe ->vivid_create_instance ->设置ctrl（用于app的ioctl）：事先添加属性 例如dev->brightness = v4l2_ctrl_new_std(hdl_user_vid, &vivid_user_vid_ctrl_ops, V4L2_CID_BRIGHTNESS, 0, 255, 1, 128); ->v4l2_device_register // 不是主要，主要初始化一些东西，比如自旋锁，引用计数 ->video_register_device(vfd, VFL_TYPE_GRABBER, vid_cap_nr[inst]); // 根据不同的功能，实现不同的节点注册 ->__video_register_device vdev->cdev = cdev_alloc(); vdev->cdev->ops = &v4l2_fops; cdev_add 分析vivid的open、read、write、ioctl过程： app: open("/dev/video0",...) -------------------------------------------------------------------------------- drv: v4l2_open vdev = video_devdata(filp); // 根据次设备号从数组中得到video_device ret = vdev->fops->open(filp); // 也就是vivid_fops->v4l2_fh_open函数 app: ioctl -------------------------------------------------------------------------------- drv: v4l2_fops.unlocked_ioctl v4l2-ioctl struct video_device vdev = video_devdata(filp); ret = vdev->fops->unlocked_ioctl(filp, cmd, arg); video_ioctl2 video_usercopy(file, cmd, arg, __video_do_ioctl); __video_do_ioctl struct video_device *vfd = video_devdata(file); 根据app传入的cmn来获取设置某些属性
如何填写v4l2驱动：
1、分配设置注册v4l2_device：v4l2_device_register，得到v4l2_device（辅助作用，提供自旋锁引用计数）
2、分配设置注册一个video_device结构体，video_register_device，video_device.v4l2_device指向第一步分配的v4l2_device
3、video_device.v4l2_file_operations会被上层应用调用到的open/read/ioctl所调用
4、video_device.v4l2_ioctl_ops会被上层应用调用到的ioctl所间接调用
5、app可以通过ioctl来设置亮度等等信息，驱动程序使用v4l2_ctrl属性来表示接收存储设置到硬件
属性：v4l2_ctrl
管理：v4l2_ctrl_handler
初始化一个v4l2_ctrl_hander：v4l2_ctrl_handler_init
添加v4l2_ctrl属性项：v4l2_ctrl_new_std和v4l2_ctrl_new_custom，创建个个v4l2_ctrl，放入v4l2_ctrl_handler管理的链表
6、v4l2_dev.ctrl_handler和video_dev->v4l2_dev相关联
v4l2_vtrl_handler的使用过程： IOCTL_INFO_FNC(VIDIOC_QUERYCTRL, v4l_queryctrl, v4l_print_queryctrl, INFO_FL_CTRL | INFO_FL _CLEAR(v4l2_queryctrl, id)), -> static int v4l_queryctrl(const struct v4l2_ioctl_ops *ops, struct file *file, void *fh, void *arg) { struct video_device *vfd = video_devdata(file); struct v4l2_queryctrl *p = arg; struct v4l2_fh *vfh = test_bit(V4L2_FL_USES_V4L2_FH, &vfd->flags) ? fh : NULL; if (vfh && vfh->ctrl_handler) return v4l2_queryctrl(vfh->ctrl_handler, p); if (vfd->ctrl_handler) return v4l2_queryctrl(vfd->ctrl_handler, p); if (ops->vidioc_queryctrl) return ops->vidioc_queryctrl(file, fh, p); return -ENOTTY; }
