videodev-objs:=v4l2-dev.o v4l2-ioctl.o v4l2-device.o v4l2-fh.o \
v4l2-event.o v4l2-ctrls.o v4l2-subdev.o
这是生成videodev.ko必要的文件。网上有很多讲解v4l2驱动编写的文章。推荐网址:
这是主要说用户使用:
http://linuxtv.org/downloads/v4l-dvb-apis/
这是说驱动编写:
http://lwn.net/Articles/203924/
对应的中文翻译(用户的不是很全)
http://download.csdn.net/detail/xxxxxlllllxl/7076235
我的博客将从Makefile中涉及的文件对应的头文件去分析:先从v4l2_dev.h开始
/* * * V 4 L 2 D R I V E R H E L P E R A P I * * Moved from videodev2.h//从videodev2.h中移出来的 * * Some commonly needed functions for drivers (v4l2-common.o module) */ #ifndef _V4L2_DEV_H #define _V4L2_DEV_H #include <linux/poll.h> #include <linux/fs.h> #include <linux/device.h> #include <linux/cdev.h> #include <linux/mutex.h> #include <linux/videodev2.h> #include <media/media-entity.h> #define VIDEO_MAJOR 81 //下面不同的宏生成的设备名不一样 #define VFL_TYPE_GRABBER 0 //"video" #define VFL_TYPE_VBI 1 //"vbi" #define VFL_TYPE_RADIO 2 //"radio" #define VFL_TYPE_SUBDEV 3 //"v4l-subdev" #define VFL_TYPE_MAX 4 struct v4l2_ioctl_callbacks; struct video_device; struct v4l2_device; struct v4l2_ctrl_handler; /* Flag to mark the video_device struct as registered. Drivers can clear this flag if they want to block all future device access. It is cleared by video_unregister_device. */ #define V4L2_FL_REGISTERED (0)//标记设备是否被注册 /* file->private_data points to struct v4l2_fh */ #define V4L2_FL_USES_V4L2_FH (1) //使用文件操作 /* Use the prio field of v4l2_fh for core priority checking */ #define V4L2_FL_USE_FH_PRIO (2) //文件操作中使用优先级检查 /* Priority helper functions */ //优先级帮助功能 struct v4l2_prio_state { atomic_t prios[4]; }; /* enum v4l2_priority { V4L2_PRIORITY_UNSET = 0, //不初始化 V4L2_PRIORITY_BACKGROUND = 1, //背景 V4L2_PRIORITY_INTERACTIVE = 2, //互动 V4L2_PRIORITY_RECORD = 3, //记录 V4L2_PRIORITY_DEFAULT = V4L2_PRIORITY_INTERACTIVE, }; */ //优先级是为了Multiple Opens操作,当可以支持设备同事被多个线程打开时 //需要用这优先级去区分那个操作更重要,用那个优先级,那个优先级几上面 //的prios[4]就加一,不用就减一。 void v4l2_prio_init(struct v4l2_prio_state *global); //初始化,就是global清零 int v4l2_prio_change(struct v4l2_prio_state *global, enum v4l2_priority *local, enum v4l2_priority new); //改变优先级,对应prios改变,local会等于new void v4l2_prio_open(struct v4l2_prio_state *global, enum v4l2_priority *local);//打开,对应的prios[*local]加一 void v4l2_prio_close(struct v4l2_prio_state *global, enum v4l2_priority local);//关闭,对应的prios[local]减一 enum v4l2_priority v4l2_prio_max(struct v4l2_prio_state *global);//当前已打开的最大优先级。 int v4l2_prio_check(struct v4l2_prio_state *global, enum v4l2_priority local);//检查local显示优先级是否是当前打开的最大的优先级 struct v4l2_file_operations { struct module *owner; ssize_t (*read) (struct file *, char __user *, size_t, loff_t *); ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *); unsigned int (*poll) (struct file *, struct poll_table_struct *); long (*ioctl) (struct file *, unsigned int, unsigned long); long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long); unsigned long (*get_unmapped_area) (struct file *, unsigned long, unsigned long, unsigned long, unsigned long); int (*mmap) (struct file *, struct vm_area_struct *); int (*open) (struct file *); int (*release) (struct file *); }; /* 对应上面的ops我要说几点: 1. get_unmapped_area,这个最终赋给file_operations对应的函数。 这是系统sys_mmap2使用的函数,会判断虚拟内存空间中是否有足 够的空间的工作。 2. read/write读流 使用read和write方法,每一帧都要通过I/O 操作,在用户和内核 空间之间拷贝数据。设备cap要或上V4L2_CAP_READWRITE 3. ioctl和unlocked_ioctl 这两个都通过file_operations中的unlocked_ioctl调用,v4l2的 unlocked_ioctl会优先调用,ioctl可以认为是序列化的ioctl,会 上锁等待上一个ioctl完成,如果在驱动睡眠下会很糟糕。 4. ioctl读流 在设备cap上要或上V4L2_CAP_STREAMING,让用户与内核空间之间 交换缓冲区指针,这些缓冲区将被映射到用户地址空间,使帧的零 拷贝成为可能。 “用户与内核空间之间交换缓冲区指针”我们要理解的是缓冲区是 在用户空间还是内核空间。对于内核空间我们通过mmap()方法映射。 对于用户空间就不需要mmap(),此方法比较难用。 */ /* * Newer version of video_device, handled by videodev2.c * This version moves redundant code from video device code to * the common handler */ struct video_device { #if defined(CONFIG_MEDIA_CONTROLLER) struct media_entity entity; #endif /* device ops */ const struct v4l2_file_operations *fops; /* sysfs */ struct device dev; /* v4l device */ //这个dev主要是为了sysfs用的 struct cdev *cdev; /* character device */ //这个cdev就是我们生成对应的video字符设备 /* Set either parent or v4l2_dev if your driver uses v4l2_device */ struct device *parent; /* device parent */ struct v4l2_device *v4l2_dev; /* v4l2_device parent */ /* Control handler associated with this device node. May be NULL. */ struct v4l2_ctrl_handler *ctrl_handler;//这是多video设备控制用的,等说到v4l2_ctrls.h再细说 /* Priority state. If NULL, then v4l2_dev->prio will be used. */ struct v4l2_prio_state *prio;//上面说的优先级 /* device info */ char name[32]; //设备名,这个设备名是在/sysfs下显示用的 int vfl_type; //对应上面的VFL_* /* ‘minor‘ is set to -1 if the registration failed */ int minor; u16 num;//记录注册的video设备节点号 /* use bitops to set/clear/test flags */ unsigned long flags;//主要对应上面的V4L2_FL_* /* attribute to differentiate multiple indices on one physical device */ int index;//通过get_index()获取一个可用设备索引。 /* V4L2 file handles *///文件操作。v4l2_fh.h再说 spinlock_t fh_lock; /* Lock for all v4l2_fhs */ struct list_head fh_list; /* List of struct v4l2_fh */ int debug; /* Activates debug level*///V4L2_DEBUG_*,不同的赋值,打印出的信息数量不一样 /* Video standard vars */ //视频标准规范,对应V4L2_STD_*,如我们熟悉的PAL、NTSC。 v4l2_std_id tvnorms; /* Supported tv norms */ //支持的标准 v4l2_std_id current_norm; /* Current tvnorm */ //当前使用的标准 /* callbacks */ void (*release)(struct video_device *vdev);//这个必须有,很多驱动使用video_device_release。 /* ioctl callbacks */ //v4l2-ioctl.h我们再慢慢说它 const struct v4l2_ioctl_ops *ioctl_ops; /* serialization lock */ struct mutex *lock; }; #define media_entity_to_video_device(__e) container_of(__e, struct video_device, entity) /* dev to video-device */ #define to_video_device(cd) container_of(cd, struct video_device, dev) //这个注册主要说一下warn_if_nr_in_use,就是如果你指定一个nr,但是驱动会使用另一个代替时会打印警告 int __must_check __video_register_device(struct video_device *vdev, int type, int nr, int warn_if_nr_in_use, struct module *owner); /* Register video devices. Note that if video_register_device fails, the release() callback of the video_device structure is *not* called, so the caller is responsible for freeing any data. Usually that means that you call video_device_release() on failure. */ static inline int __must_check video_register_device(struct video_device *vdev, int type, int nr) { return __video_register_device(vdev, type, nr, 1, vdev->fops->owner); } /* Same as video_register_device, but no warning is issued if the desired device node number was already in use. */ static inline int __must_check video_register_device_no_warn( struct video_device *vdev, int type, int nr) { return __video_register_device(vdev, type, nr, 0, vdev->fops->owner); } /* Unregister video devices. Will do nothing if vdev == NULL or video_is_registered() returns false. */ void video_unregister_device(struct video_device *vdev); /* helper functions to alloc/release struct video_device, the latter can also be used for video_device->release(). */ struct video_device * __must_check video_device_alloc(void); //分配video_device结构体 /* this release function frees the vdev pointer */ void video_device_release(struct video_device *vdev); //释放 /* this release function does nothing, use when the video_device is a static global struct. Note that having a static video_device is a dubious construction at best. */ void video_device_release_empty(struct video_device *vdev);//空函数 /* helper functions to access driver private data. */ static inline void *video_get_drvdata(struct video_device *vdev) //获取私有数据 { return dev_get_drvdata(&vdev->dev); } static inline void video_set_drvdata(struct video_device *vdev, void *data)//设置私有数据 { dev_set_drvdata(&vdev->dev, data); } struct video_device *video_devdata(struct file *file);//根据file得到对应的video_device /* Combine video_get_drvdata and video_devdata as this is used very often. */ static inline void *video_drvdata(struct file *file) //结合上面看 { return video_get_drvdata(video_devdata(file)); } static inline const char *video_device_node_name(struct video_device *vdev) { return dev_name(&vdev->dev); } static inline int video_is_registered(struct video_device *vdev)//是否已注册 { return test_bit(V4L2_FL_REGISTERED, &vdev->flags); } #endif /* _V4L2_DEV_H */