V4L2应用程序框架-二【转】

本文转载自：http://blog.csdn.net/tommy_wxie/article/details/11371439

V4L2驱动框架

主设备号： 81

次设备号：
    0-63
    64-67
    192-223
    224-255

/dev/videoX

应用层
————————————
char驱动
————————————
V4L2
————————————
具体的驱动
————————————
硬件

应用层的操作都需要有底层V4L2驱动的支持。内核中有一些非常完善的例子。比如：linux-2.6.26内核目录drivers/media/video/vivi.c中的驱动代码实例。

1、V4L2驱动注册、注销函数
static int __init videodev_init(void)        //注册256个视频设备
{
        dev_t dev = MKDEV(VIDEO_MAJOR, 0);
        int ret;

printk(KERN_INFO "Linux video capture interface: v2.00\n");
        ret = register_chrdev_region(dev, VIDEO_NUM_DEVICES, VIDEO_NAME);
        if (ret < 0) {
                printk(KERN_WARNING "videodev: unable to get major %d\n", VIDEO_MAJOR);
                return ret;
        }

ret = class_register(&video_class);
        if (ret < 0) {
                unregister_chrdev_region(dev, VIDEO_NUM_DEVICES);
                printk(KERN_WARNING "video_dev: class_register failed\n");
                return -EIO;
        }

return 0;
}

static void __exit videodev_exit(void)
{
        dev_t dev = MKDEV(VIDEO_MAJOR, 0);

class_unregister(&video_class);
        unregister_chrdev_region(dev, VIDEO_NUM_DEVICES);
}

module_init(videodev_init)
module_exit(videodev_exit)

2、函数实现

2.1
Video核心层（drivers/media/video/videodev.c）提供了注册函数供具体的V4L2驱动调用:
int video_register_device(struct video_device *vfd, int type, int nr)
    —video_device: 要构建的核心数据结构
    —Type: 表示设备类型，此设备号的基地址受此变量的影响
    —Nr: 如果end-base>nr>0 ：次设备号=base（基准值，受type影响）+nr；否则：系统自动分配合适的次设备号

函数内部调用
static int __video_register_device(struct video_device *vdev, int type, int nr, int warn_if_nr_in_use)
具体驱动只需要构建video_device结构，然后调用注册函数既可。

2.2
Video核心层（drivers/media/video/videodev.c）提供了注销函数
void video_unregister_device(struct video_device *vdev)

核心定义设备数组，其中VIDEO_NUM_DEVICES 为 256 是最大设备数
static struct video_device *video_device[VIDEO_NUM_DEVICES];

2.3
V4L2提供了统一的应用层接口

static const struct file_operations v4l2_fops = {
        .owner = THIS_MODULE,
        .read = v4l2_read,
        .write = v4l2_write,
        .open = v4l2_open,
        .mmap = v4l2_mmap,
        .unlocked_ioctl = v4l2_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl = v4l2_compat_ioctl32,
#endif
        .release = v4l2_release,
        .poll = v4l2_poll,
        .llseek = no_llseek,
};
v4l2_read定义如下
static ssize_t v4l2_read(struct file *filp, char __user *buf, size_t sz, loff_t *off)
{
        struct video_device *vdev = video_devdata(filp);
        int ret = -ENODEV;

if (!vdev->fops->read)
                return -EINVAL;
        if (vdev->lock && mutex_lock_interruptible(vdev->lock))
                return -ERESTARTSYS;
        if (video_is_registered(vdev))
                ret = vdev->fops->read(filp, buf, sz, off);
        if (vdev->lock)
                mutex_unlock(vdev->lock);
        return ret;
}

函数内部调用的    vdev->fops->read  由具体的V4L2驱动实现

驱动开发

定义最重要的数据结构体struct video_device，
其中，重要的是
const struct v4l2_file_operations *fops;    //帧缓冲操作

编写帧缓冲驱动的主要工作就是编写fops各个成员函数

编写具体驱动方法步骤:
1、构建具体驱动的struct video_device;
3、构建具体驱动的struct fops,并定义相关的操作函数；

4、定义具体驱动的XXX_probe。

struct video_device
{
        /* device ops */
        const struct v4l2_file_operations *fops;

/* sysfs */
        struct device dev;              /* v4l device */
        struct cdev *cdev;              /* character device */

/* 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;

/* device info */
        char name[32];
        int vfl_type;
        /* 'minor' is set to -1 if the registration failed */
        int minor;
        u16 num;
        /* use bitops to set/clear/test flags */
        unsigned long flags;
        /* attribute to differentiate multiple indices on one physical device */
        int index;

/* V4L2 file handles */
        spinlock_t              fh_lock; /* Lock for all v4l2_fhs */
        struct list_head        fh_list; /* List of struct v4l2_fh */

int debug;                      /* Activates debug level*/

/* Video standard vars */
        v4l2_std_id tvnorms;            /* Supported tv norms */
        v4l2_std_id current_norm;       /* Current tvnorm */

/* callbacks */
        void (*release)(struct video_device *vdev);

/* ioctl callbacks */
        const struct v4l2_ioctl_ops *ioctl_ops;

/* serialization lock */
        struct mutex *lock;
};
================================================================================
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);
        int (*mmap) (struct file *, struct vm_area_struct *);
        int (*open) (struct file *);
        int (*release) (struct file *);
};
================================================================================
struct device {
        struct device           *parent;
        struct device_private   *p;
        struct kobject kobj;
        const char              *init_name;/* initial name of the device */
        struct device_type      *type;
        struct mutex            mutex;      /* mutex to synchronize calls to its driver. */
        struct bus_type *bus;               /* type of bus device is on */
        struct device_driver     *driver;    /* which driver has allocated this device */
        void                *platform_data; /* Platform specific data, device core doesn't touch it */
        struct dev_pm_info      power;
#ifdef CONFIG_NUMA
        int                 numa_node;      /* NUMA node this device is close to */
#endif
        u64                 *dma_mask;      /* dma mask (if dma'able device) */
        u64                 coherent_dma_mask;/* Like dma_mask, but for alloc_coherent mappings as not all hardware supports 64 bit ses for consistent allocations such descriptors. */
        struct device_dma_parameters *dma_parms;
        struct list_head        dma_pools;      /* dma pools (if dma'ble) */
        struct dma_coherent_mem *dma_mem; /* internal for coherent mem override */
        /* arch specific additions */
        struct dev_archdata     archdata;
#ifdef CONFIG_OF
        struct device_node      *of_node;
#endif
        dev_t                   devt;   /* dev_t, creates the sysfs "dev" */
        spinlock_t              devres_lock;
        struct list_head        devres_head;
        struct klist_node       knode_class;
        struct class            *class;
        const struct attribute_group **groups;  /* optional groups */
        void    (*release)(struct device *dev);
};
================================================================================
struct cdev {
        struct kobject kobj;
        struct module *owner;
        const struct file_operations *ops;
        struct list_head list;
        dev_t dev;
        unsigned int count;
};
================================================================================
struct v4l2_device {
        struct device *dev;    /* dev->driver_data points to this struct. Note: dev might be NULL if there is no parent device as is the case with e.g. ISA devices. */
        struct list_head subdevs;          /* used to keep track of the registered subdevs */
        spinlock_t lock;  /* lock this struct; can be used by the driver as well if this struct is embedded into a larger struct. */
        char name[V4L2_DEVICE_NAME_SIZE];        /* unique device name, by default the driver name + bus ID */
        void (*notify)(struct v4l2_subdev *sd, unsigned int notification, void *arg);        /* notify callback called by some sub-devices. */
        struct v4l2_ctrl_handler *ctrl_handler;        /* The control handler. May be NULL. */
        struct mutex ioctl_lock;        /* BKL replacement mutex. Temporary solution only. */
};
================================================================================
struct v4l2_ioctl_ops {
        /* ioctl callbacks */
        /* VIDIOC_QUERYCAP handler */
        int (*vidioc_querycap)(struct file *file, void *fh, struct v4l2_capability *cap);
        /* Priority handling */
        int (*vidioc_g_priority)   (struct file *file, void *fh, enum v4l2_priority *p);
        int (*vidioc_s_priority)   (struct file *file, void *fh, enum v4l2_priority p);
        /* VIDIOC_ENUM_FMT handlers */
        int (*vidioc_enum_fmt_vid_cap)     (struct file *file, void *fh, struct v4l2_fmtdesc *f);
        int (*vidioc_enum_fmt_vid_overlay) (struct file *file, void *fh, struct v4l2_fmtdesc *f);
        int (*vidioc_enum_fmt_vid_out)     (struct file *file, void *fh, struct v4l2_fmtdesc *f);
        int (*vidioc_enum_fmt_type_private)(struct file *file, void *fh, struct v4l2_fmtdesc *f);
        /* VIDIOC_G_FMT handlers */
        int (*vidioc_g_fmt_vid_cap)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_g_fmt_vid_overlay)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_g_fmt_vid_out)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_g_fmt_vid_out_overlay)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_g_fmt_vbi_cap)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_g_fmt_vbi_out)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_g_fmt_sliced_vbi_cap)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_g_fmt_sliced_vbi_out)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_g_fmt_type_private)(struct file *file, void *fh, struct v4l2_format *f);
        /* VIDIOC_S_FMT handlers */
        int (*vidioc_s_fmt_vid_cap)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_s_fmt_vid_overlay)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_s_fmt_vid_out)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_s_fmt_vid_out_overlay)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_s_fmt_vbi_cap)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_s_fmt_vbi_out)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_s_fmt_sliced_vbi_cap)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_s_fmt_sliced_vbi_out)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_s_fmt_type_private)(struct file *file, void *fh, struct v4l2_format *f);
        /* VIDIOC_TRY_FMT handlers */
        int (*vidioc_try_fmt_vid_cap)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_try_fmt_vid_overlay)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_try_fmt_vid_out)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_try_fmt_vid_out_overlay)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_try_fmt_vbi_cap)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_try_fmt_vbi_out)    (struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_try_fmt_sliced_vbi_cap)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_try_fmt_sliced_vbi_out)(struct file *file, void *fh, struct v4l2_format *f);
        int (*vidioc_try_fmt_type_private)(struct file *file, void *fh, struct v4l2_format *f);
        /* Buffer handlers */
        int (*vidioc_reqbufs) (struct file *file, void *fh, struct v4l2_requestbuffers *b);
        int (*vidioc_querybuf)(struct file *file, void *fh, struct v4l2_buffer *b);
        int (*vidioc_qbuf)    (struct file *file, void *fh, struct v4l2_buffer *b);
        int (*vidioc_dqbuf)   (struct file *file, void *fh, struct v4l2_buffer *b);
        int (*vidioc_overlay)    (struct file *file, void *fh, unsigned int i);
        int (*vidioc_g_fbuf)    (struct file *file, void *fh, struct v4l2_framebuffer *a);
        int (*vidioc_s_fbuf)    (struct file *file, void *fh, struct v4l2_framebuffer *a);
        /* Stream on/off */
        int (*vidioc_streamon)    (struct file *file, void *fh, enum v4l2_buf_type i);
        int (*vidioc_streamoff)    (struct file *file, void *fh, enum v4l2_buf_type i);
        /* Standard handling ENUMSTD is handled by videodev.c */
        int (*vidioc_g_std)     (struct file *file, void *fh, v4l2_std_id *norm);
        int (*vidioc_s_std)     (struct file *file, void *fh, v4l2_std_id *norm);
        int (*vidioc_querystd)     (struct file *file, void *fh, v4l2_std_id *a);
        /* Input handling */
        int (*vidioc_enum_input)    (struct file *file, void *fh, struct v4l2_input *inp);
        int (*vidioc_g_input)       (struct file *file, void *fh, unsigned int *i);
        int (*vidioc_s_input)       (struct file *file, void *fh, unsigned int i);
        /* Output handling */
        int (*vidioc_enum_output)    (struct file *file, void *fh, struct v4l2_output *a);
        int (*vidioc_g_output)       (struct file *file, void *fh, unsigned int *i);
        int (*vidioc_s_output)       (struct file *file, void *fh, unsigned int i);
        /* Control handling */
        int (*vidioc_queryctrl)        (struct file *file, void *fh, struct v4l2_queryctrl *a);
        int (*vidioc_g_ctrl)           (struct file *file, void *fh, struct v4l2_control *a);
        int (*vidioc_s_ctrl)           (struct file *file, void *fh, struct v4l2_control *a);
        int (*vidioc_g_ext_ctrls)      (struct file *file, void *fh, struct v4l2_ext_controls *a);
        int (*vidioc_s_ext_ctrls)      (struct file *file, void *fh, struct v4l2_ext_controls *a);
        int (*vidioc_try_ext_ctrls)    (struct file *file, void *fh, struct v4l2_ext_controls *a);
        int (*vidioc_querymenu)        (struct file *file, void *fh, struct v4l2_querymenu *a);
        /* Audio ioctls */
        int (*vidioc_enumaudio)        (struct file *file, void *fh, struct v4l2_audio *a);
        int (*vidioc_g_audio)          (struct file *file, void *fh, struct v4l2_audio *a);
        int (*vidioc_s_audio)          (struct file *file, void *fh, struct v4l2_audio *a);
        /* Audio out ioctls */
        int (*vidioc_enumaudout)       (struct file *file, void *fh, struct v4l2_audioout *a);
        int (*vidioc_g_audout)         (struct file *file, void *fh, struct v4l2_audioout *a);
        int (*vidioc_s_audout)         (struct file *file, void *fh, struct v4l2_audioout *a);
        int (*vidioc_g_modulator)      (struct file *file, void *fh, struct v4l2_modulator *a);
        int (*vidioc_s_modulator)      (struct file *file, void *fh, struct v4l2_modulator *a);
        /* Crop ioctls */
        int (*vidioc_cropcap)          (struct file *file, void *fh, struct v4l2_cropcap *a);
        int (*vidioc_g_crop)           (struct file *file, void *fh, struct v4l2_crop *a);
        int (*vidioc_s_crop)           (struct file *file, void *fh, struct v4l2_crop *a);
        /* Compression ioctls */
        int (*vidioc_g_jpegcomp)       (struct file *file, void *fh, struct v4l2_jpegcompression *a);
        int (*vidioc_s_jpegcomp)       (struct file *file, void *fh, struct v4l2_jpegcompression *a);
        int (*vidioc_g_enc_index)      (struct file *file, void *fh, struct v4l2_enc_idx *a);
        int (*vidioc_encoder_cmd)      (struct file *file, void *fh, struct v4l2_encoder_cmd *a);
        int (*vidioc_try_encoder_cmd)  (struct file *file, void *fh, struct v4l2_encoder_cmd *a);
        /* Stream type-dependent parameter ioctls */
        int (*vidioc_g_parm)           (struct file *file, void *fh, struct v4l2_streamparm *a);
        int (*vidioc_s_parm)           (struct file *file, void *fh, struct v4l2_streamparm *a);
        /* Tuner ioctls */
        int (*vidioc_g_tuner)          (struct file *file, void *fh, struct v4l2_tuner *a);
        int (*vidioc_s_tuner)          (struct file *file, void *fh, struct v4l2_tuner *a);
        int (*vidioc_g_frequency)      (struct file *file, void *fh, struct v4l2_frequency *a);
        int (*vidioc_s_frequency)      (struct file *file, void *fh, struct v4l2_frequency *a);
        /* Sliced VBI cap */
        int (*vidioc_g_sliced_vbi_cap) (struct file *file, void *fh, struct v4l2_sliced_vbi_cap *a);
        /* Log status ioctl */
        int (*vidioc_log_status)       (struct file *file, void *fh);
        int (*vidioc_s_hw_freq_seek)   (struct file *file, void *fh, struct v4l2_hw_freq_seek *a);
        /* Debugging ioctls */
#ifdef CONFIG_VIDEO_ADV_DEBUG
        int (*vidioc_g_register)       (struct file *file, void *fh, struct v4l2_dbg_register *reg);
        int (*vidioc_s_register)       (struct file *file, void *fh, struct v4l2_dbg_register *reg);
#endif
        int (*vidioc_g_chip_ident)       (struct file *file, void *fh, struct v4l2_dbg_chip_ident *chip);
        int (*vidioc_enum_framesizes)      (struct file *file, void *fh, struct v4l2_frmsizeenum *fsize);
        int (*vidioc_enum_frameintervals)  (struct file *file, void *fh, struct v4l2_frmivalenum *fival);
        /* DV Timings IOCTLs */
        int (*vidioc_enum_dv_presets)  (struct file *file, void *fh, struct v4l2_dv_enum_preset *preset);
        int (*vidioc_s_dv_preset)      (struct file *file, void *fh, struct v4l2_dv_preset *preset);
        int (*vidioc_g_dv_preset)      (struct file *file, void *fh, struct v4l2_dv_preset *preset);
        int (*vidioc_query_dv_preset)  (struct file *file, void *fh, struct v4l2_dv_preset *qpreset);
        int (*vidioc_s_dv_timings)     (struct file *file, void *fh, struct v4l2_dv_timings *timings);
        int (*vidioc_g_dv_timings)     (struct file *file, void *fh, struct v4l2_dv_timings *timings);
        int (*vidioc_subscribe_event)  (struct v4l2_fh *fh, struct v4l2_event_subscription *sub);
        int (*vidioc_unsubscribe_event)(struct v4l2_fh *fh, struct v4l2_event_subscription *sub);
        /* For other private ioctls */
        long (*vidioc_default)         (struct file *file, void *fh, int cmd, void *arg);
};

================================================================================

================================================================================

================================================================================

static struct ov7670_format_struct {
        enum v4l2_mbus_pixelcode mbus_code;
        enum v4l2_colorspace colorspace;
        struct regval_list *regs;
        int cmatrix[CMATRIX_LEN];
    int bpp;
} ov7670_format_struct ov7670_formats[] = {
    /* "YUYV 4:2:2"     */
        .desc        = "YUYV 4:2:2",
        .pixelformat    = V4L2_PIX_FMT_YUYV,
        .regs         = ov7670_fmt_yuv422,
        .cmatrix    = { 128, -128, 0, -34, -94, 128 },
        .bpp        = 2,
    /* "UYVY 4:2:2"     */
    /* "RGB 444"        */
    /* "RGB 565"        */
    /* "Raw RGB Bayer"  */
}
#define N_OV7670_FMTS ARRAY_SIZE(ov7670_formats)

struct v4l2_fmtdesc {
        __u32               index;             /* Format number      */
        enum v4l2_buf_type  type;              /* buffer type        */
        __u32               flags;
        __u8                description[32];   /* Description string */
        __u32               pixelformat;       /* Format fourcc      */
        __u32               reserved[4];
};
 
//每一个subdev驱动程序实例应该创建这个结构，无论是独立或在一个更大的结构之中。
struct v4l2_subdev {
        struct list_head list;
        struct module *owner;
        u32 flags;
        struct v4l2_device *v4l2_dev;
        const struct v4l2_subdev_ops *ops;
        /* name must be unique */
        char name[V4L2_SUBDEV_NAME_SIZE];
        /* can be used to group similar subdevs, value is driver-specific */
        u32 grp_id; 
        /* pointer to private data */
        void *priv;
}; 
struct v4l2_pix_format { 
        __u32                   width;
        __u32                   height;
        __u32                   pixelformat;
        enum v4l2_field         field;
        __u32                   bytesperline;   /* for padding, zero if unused */
        __u32                   sizeimage;
        enum v4l2_colorspace    colorspace;
        __u32                   priv;           /* private data, depends on pixelformat */
};

struct v4l2_format { 
        enum v4l2_buf_type type;
        union { 
                struct v4l2_pix_format          pix;     /* V4L2_BUF_TYPE_VIDEO_CAPTURE */
                struct v4l2_window              win;     /* V4L2_BUF_TYPE_VIDEO_OVERLAY */
                struct v4l2_vbi_format          vbi;     /* V4L2_BUF_TYPE_VBI_CAPTURE */
                struct v4l2_sliced_vbi_format   sliced;  /* V4L2_BUF_TYPE_SLICED_VBI_CAPTURE */
                __u8    raw_data[200];                   /* user-defined */
        } fmt;
};

static struct ov7670_win_size {
        int     width;
        int     height;
        unsigned char com7_bit;
        int     hstart;         /* Start/stop values for the camera.  Note */
        int     hstop;          /* that they do not always make complete */
        int     vstart;         /* sense to humans, but evidently the sensor */
        int     vstop;          /* will do the right thing... */
        struct regval_list *regs; /* Regs to tweak */
                /* h/vref stuff */
} ov7670_win_sizes[] = {
    /* VGA */
    /* CIF */
    /* QVGA */
    /* QCIF */
}
#define N_WIN_SIZES (ARRAY_SIZE(ov7670_win_sizes))