Camera V4L2 架构分析
来源:互联网 发布:角度弧度转换器软件 编辑:程序博客网 时间:2024/05/21 07:57
转自:点击打开链接
V4L2相关代码位于linux-3.4/drivers/media/video目录中。
v4l2-dev.c文件提供设备节点实现与用户层数据交流,设备节点在/dev/目录下以video0、video1等名字出现。注册字符设备的语句如下:
-
- vdev->cdev = cdev_alloc();
- if (vdev->cdev == NULL) {
- ret = -ENOMEM;
- goto cleanup;
- }
- vdev->cdev->ops = &v4l2_fops;
- vdev->cdev->owner = owner;
- ret = cdev_add(vdev->cdev, MKDEV(VIDEO_MAJOR, vdev->minor), 1);
- if (ret < 0) {
- printk(KERN_ERR "%s: cdev_add failed\n", __func__);
- kfree(vdev->cdev);
- vdev->cdev = NULL;
- goto cleanup;
- }
-
-
- vdev->dev.class = &video_class;
- vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor);
- if (vdev->parent)
- vdev->dev.parent = vdev->parent;
- dev_set_name(&vdev->dev, "%s%d", name_base, vdev->num);
- ret = device_register(&vdev->dev);
只要调用函数video_register_device即可把一个video_device注册到V4L2架构中;但这只是一个总纲领,Camera驱动主要是实现V4L2的一个子系统的功能,子系统用一个v4l2_subdev结构体来描述,只有实现好了系统要求的相关函数操作,最后一步才是注册到V4L2中。子系统实现的方式每个平台都有差别,这里分析的是全志A23平台的代码。
在sunxi-vfe/vfe.c文件中,以platform形式注册了前后摄像头的平台资源。匹配过程忽略,最终vfe_probe函数会被调用。在probe中,看到有函数v4l2_i2c_new_subdev_board:
-
- if (info->addr == 0 && probe_addrs)
- client = i2c_new_probed_device(adapter, info, probe_addrs,
- NULL);
- else
- client = i2c_new_device(adapter, info);
- ...............................
-
-
- if (v4l2_device_register_subdev(v4l2_dev, sd))
- sd = NULL;
这里的client获得在之前写的I2C驱动的文章已经分析过,可见驱动的知识都是环环相扣的;根据I2C驱动文章的分析可知获取client过程中,device_register(&client->dev)会被调用,而根据device和device_driver的模型关系可知,device所在的bus总线会进行匹配,device处于i2c总线下,根据I2C match函数的匹配,名字相同的device_driver将被匹配中;我们假设i2c_client的name为"ov5460"吧,这样ov5460.c中看看:- static struct i2c_driver sensor_driver = {
- .driver = {
- .owner = THIS_MODULE,
- .name = SENSOR_NAME,
- },
- .probe = sensor_probe,
- .remove = sensor_remove,
- .id_table = sensor_id,
- };
毫无疑问,sensor_probe函数会被调用了:- static int sensor_probe(struct i2c_client *client,
- const struct i2c_device_id *id)
- {
- struct v4l2_subdev *sd;
- struct sensor_info *info;
-
-
- info = kzalloc(sizeof(struct sensor_info), GFP_KERNEL);
- if (info == NULL)
- return -ENOMEM;
- sd = &info->sd;
- glb_sd = sd;
- v4l2_i2c_subdev_init(sd, client, &sensor_ops);
-
- info->fmt = &sensor_formats[0];
- info->af_first_flag = 1;
- info->init_first_flag = 1;
- info->auto_focus = 0;
-
- return 0;
- }
这里就看到了前面提到的v4l2_subdev结构体,v4l2_i2c_subdev_init函数会进入v4l2-subdev.c进行一系列初始化操作,并且用i2c_set_clientdata(client, sd);保存子系统指针,以便后续取出。这里sensor_ops结构体即为子系统支持的类型:- static const struct v4l2_subdev_ops sensor_ops = {
- .core = &sensor_core_ops,
- .video = &sensor_video_ops,
- };
Camera当然是是video的了,core是核心,应该是不可少的操作吧。其实v4l2_subdev所支持的类型很多,其全部类型定义如下:- struct v4l2_subdev_ops {
- const struct v4l2_subdev_core_ops *core;
- const struct v4l2_subdev_tuner_ops *tuner;
- const struct v4l2_subdev_audio_ops *audio;
- const struct v4l2_subdev_video_ops *video;
- const struct v4l2_subdev_vbi_ops *vbi;
- const struct v4l2_subdev_ir_ops *ir;
- const struct v4l2_subdev_sensor_ops *sensor;
- const struct v4l2_subdev_pad_ops *pad;
- };
tuner应该属于电视一类的吧,还有ir,红外;audio,音频等。看看video要实现的操作:- struct v4l2_subdev_video_ops {
- int (*s_routing)(struct v4l2_subdev *sd, u32 input, u32 output, u32 config);
- int (*s_crystal_freq)(struct v4l2_subdev *sd, u32 freq, u32 flags);
- int (*s_std_output)(struct v4l2_subdev *sd, v4l2_std_id std);
- int (*g_std_output)(struct v4l2_subdev *sd, v4l2_std_id *std);
- int (*querystd)(struct v4l2_subdev *sd, v4l2_std_id *std);
- int (*g_tvnorms_output)(struct v4l2_subdev *sd, v4l2_std_id *std);
- int (*g_input_status)(struct v4l2_subdev *sd, u32 *status);
- int (*s_stream)(struct v4l2_subdev *sd, int enable);
- int (*cropcap)(struct v4l2_subdev *sd, struct v4l2_cropcap *cc);
- int (*g_crop)(struct v4l2_subdev *sd, struct v4l2_crop *crop);
- int (*s_crop)(struct v4l2_subdev *sd, struct v4l2_crop *crop);
- int (*g_parm)(struct v4l2_subdev *sd, struct v4l2_streamparm *param);
- int (*s_parm)(struct v4l2_subdev *sd, struct v4l2_streamparm *param);
- int (*g_frame_interval)(struct v4l2_subdev *sd,
- struct v4l2_subdev_frame_interval *interval);
- int (*s_frame_interval)(struct v4l2_subdev *sd,
- struct v4l2_subdev_frame_interval *interval);
- int (*enum_framesizes)(struct v4l2_subdev *sd, struct v4l2_frmsizeenum *fsize);
- int (*enum_frameintervals)(struct v4l2_subdev *sd, struct v4l2_frmivalenum *fival);
- int (*enum_dv_presets) (struct v4l2_subdev *sd,
- struct v4l2_dv_enum_preset *preset);
- int (*s_dv_preset)(struct v4l2_subdev *sd,
- struct v4l2_dv_preset *preset);
- int (*g_dv_preset)(struct v4l2_subdev *sd,
- struct v4l2_dv_preset *preset);
- int (*query_dv_preset)(struct v4l2_subdev *sd,
- struct v4l2_dv_preset *preset);
- int (*s_dv_timings)(struct v4l2_subdev *sd,
- struct v4l2_dv_timings *timings);
- int (*g_dv_timings)(struct v4l2_subdev *sd,
- struct v4l2_dv_timings *timings);
- int (*enum_mbus_fmt)(struct v4l2_subdev *sd, unsigned int index,
- enum v4l2_mbus_pixelcode *code);
- int (*enum_mbus_fsizes)(struct v4l2_subdev *sd,
- struct v4l2_frmsizeenum *fsize);
- int (*g_mbus_fmt)(struct v4l2_subdev *sd,
- struct v4l2_mbus_framefmt *fmt);
- int (*try_mbus_fmt)(struct v4l2_subdev *sd,
- struct v4l2_mbus_framefmt *fmt);
- int (*s_mbus_fmt)(struct v4l2_subdev *sd,
- struct v4l2_mbus_framefmt *fmt);
- int (*g_mbus_config)(struct v4l2_subdev *sd,
- struct v4l2_mbus_config *cfg);
- int (*s_mbus_config)(struct v4l2_subdev *sd,
- const struct v4l2_mbus_config *cfg);
- };
太多了,这就是一个具体摄像头主要实现的操作,而ov5640只是支持其中一部分操作而已:- static const struct v4l2_subdev_core_ops sensor_core_ops = {
- .g_chip_ident = sensor_g_chip_ident,
- .g_ctrl = sensor_g_ctrl,
- .s_ctrl = sensor_s_ctrl,
- .queryctrl = sensor_queryctrl,
- .reset = sensor_reset,
- .init = sensor_init,
- .s_power = sensor_power,
- .ioctl = sensor_ioctl,
- };
- static const struct v4l2_subdev_video_ops sensor_video_ops = {
- .enum_mbus_fmt = sensor_enum_fmt,
- .enum_framesizes = sensor_enum_size,
- .try_mbus_fmt = sensor_try_fmt,
- .s_mbus_fmt = sensor_s_fmt,
- .s_parm = sensor_s_parm,
- .g_parm = sensor_g_parm,
- .g_mbus_config = sensor_g_mbus_config,
- };
这样回到v4l2_i2c_new_subdev_board函数中,调用v4l2_device_register_subdev把sd注册到了子系统中去。
回到vfe.c的probe函数中。常用到的操作是v4l2_subdev_call,其实这是一个宏:
- #define v4l2_subdev_call(sd, o, f, args...) \
- (!(sd) ? -ENODEV : (((sd)->ops->o && (sd)->ops->o->f) ? \
- (sd)->ops->o->f((sd) , ##args) : -ENOIOCTLCMD))
好处在于检查子系统是否支持某个操作,比如上述ov5640的,只支持sensor_core_ops和sensor_video_ops所定义的操作。其他的返回error。最后:
- vfd = video_device_alloc();
- *vfd = vfe_template;
- ret = video_register_device(vfd, VFL_TYPE_GRABBER, dev->id);
分配video_device空间并赋值,赋值内容如下:
- static struct video_device vfe_template = {
- .name = "vfe",
- .fops = &vfe_fops,
- .ioctl_ops = &vfe_ioctl_ops,
- .release = video_device_release,
- };
最后注册到了V4L2系统中。
如果从上层ioctl调用开始分析,vdev->fops->ioctl(filp, cmd, arg);调用的就是这里的vfe_fops:
- static const struct v4l2_file_operations vfe_fops = {
- .owner = THIS_MODULE,
- .open = vfe_open,
- .release = vfe_close,
- .read = vfe_read,
- .poll = vfe_poll,
- .ioctl = video_ioctl2,
-
- .mmap = vfe_mmap,
- };
video_ioctl2是要调用v4l2-ioctl.c通用的ioctl来处理,它会检查用户空间参数时候合法等操作。在该文件中调用__video_do_ioctl函数,包含了所有V4L2支持的ioctl操作命令,函数很长,代码就不贴出来了;在该ioctl中最终才调用vfe_ioctl_ops的操作:- static const struct v4l2_ioctl_ops vfe_ioctl_ops = {
- .vidioc_querycap = vidioc_querycap,
- .vidioc_enum_fmt_vid_cap = vidioc_enum_fmt_vid_cap,
- .vidioc_enum_framesizes = vidioc_enum_framesizes,
- .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_reqbufs = vidioc_reqbufs,
- .vidioc_querybuf = vidioc_querybuf,
- .vidioc_qbuf = vidioc_qbuf,
- .vidioc_dqbuf = vidioc_dqbuf,
- .vidioc_enum_input = vidioc_enum_input,
- .vidioc_g_input = vidioc_g_input,
- .vidioc_s_input = vidioc_s_input,
- .vidioc_streamon = vidioc_streamon,
- .vidioc_streamoff = vidioc_streamoff,
- .vidioc_queryctrl = vidioc_queryctrl,
- .vidioc_g_ctrl = vidioc_g_ctrl,
- .vidioc_s_ctrl = vidioc_s_ctrl,
- .vidioc_g_parm = vidioc_g_parm,
- .vidioc_s_parm = vidioc_s_parm,
- #ifdef CONFIG_VIDEO_V4L1_COMPAT
- .vidiocgmbuf = vidiocgmbuf,
- #endif
- };
而在这些通用的函数操作用,最终用v4l2_subdev_call来调用具体的Camera操作如ov5640