V4L2系列之video_register_device函数分析

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感觉写完了其实也没怎么理解这个函数，但是还是这里保存一下，希望大家予以拍砖指导：

下面分析一下video_register_device这个函数：位于include/media/v4l2-dev.h头文件中：

参考文献：http://blog.sina.com.cn/s/blog_602f87700101a52s.html

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);

}

video_register_device函数：

其中：第一个参数struct video_device *vdev是想注册的video device的结构体；

第二个参数是视频设备类型，在此头文件(v4l2-dev.h中)，定义了几种视频设备类型：

#defineVFL_TYPE_GRABBER 0 //图像采集设备

#defineVFL_TYPE_VBI 1 //从视频消隐的时间段获得信息的设备

#defineVFL_TYPE_RADIO 2 //无线电设备

#defineVFL_TYPE_SUBDEV 3 //视频设备（不确定）

#defineVFL_TYPE_MAX 4 //最大值

第三个参数是注册的设备节点号；

video_register_device函数主要是注册一个V4L2device，指定类型，然后指定device node number。函数只是简单的调用了__video_register_device函数。

按照参考文档的说明：这个__video_register_device函数主要做的工作有：1、初始化一些值；2、创建字符模式驱动；3、注册字符设备等。

下面我来分析这个函数，这个函数的定义在v4l2-dev.c中，声明在v4l2-dev.h中：

int__video_register_device(struct video_device *vdev, int type, int nr,

int warn_if_nr_in_use, struct module *owner)

前三个参数与video_register_device中相同，第四个参数不知道，第五个参数表面指向当前的模块；

int i =0;

intret;

intminor_offset = 0;

intminor_cnt = VIDEO_NUM_DEVICES;

constchar *name_base;

声明了一些变量；其中minor_cnt的赋值VIDEO_NUM_DEVICES仍定义在v4l2-dev.c中：

#defineVIDEO_NUM_DEVICES 256

声明最大的设备数量为256个？

/* A minor value of -1marks this video device as never

having beenregistered */

vdev->minor = -1;

-1表明这个video device从未被注册过（其实是指之前注册失败）。

/* the release callbackMUST be present */

if (WARN_ON(!vdev->release))

return -EINVAL;

声明release回调函数。

/* v4l2_fh support */

spin_lock_init(&vdev->fh_lock);

INIT_LIST_HEAD(&vdev->fh_list);

调用自旋锁和初始化链表。

下面开始进入各个部分的工作：

第一部分：

/* Part 1: check devicetype */

switch (type) {

case VFL_TYPE_GRABBER:

name_base = "video";

break;

case VFL_TYPE_VBI:

name_base = "vbi";

break;

case VFL_TYPE_RADIO:

name_base = "radio";

break;

case VFL_TYPE_SUBDEV:

name_base = "v4l-subdev";

break;

default:

printk(KERN_ERR "%s called with unknown type:%d\n",

__func__, type);

return -EINVAL;

}

根据各个类型设备的不同，取不同的设备类型名称。

vdev->vfl_type= type;

vdev->cdev= NULL;

if(vdev->v4l2_dev) {

if (vdev->v4l2_dev->dev)

vdev->parent = vdev->v4l2_dev->dev;

if (vdev->ctrl_handler == NULL)

vdev->ctrl_handler = vdev->v4l2_dev->ctrl_handler;

/* If the prio state pointer is NULL, then use the v4l2_device prio state. */

if (vdev->prio == NULL)

vdev->prio = &vdev->v4l2_dev->prio;

}

这里是填充struct video_device的一些字段。

第二部分：

注册device node number等。

/* Part 2: find a freeminor, device node number and device index. */

#ifdefCONFIG_VIDEO_FIXED_MINOR_RANGES

/* Keep the ranges for the first four types for historical

* reasons.

* Newer devices (notyet in place) should use the range

* of 128-191 and justpick the first free minor there

* (new style). */

switch (type) {

case VFL_TYPE_GRABBER:

minor_offset = 0;

minor_cnt = 64;

break;

case VFL_TYPE_RADIO:

minor_offset = 64;

minor_cnt = 64;

break;

case VFL_TYPE_VBI:

minor_offset = 224;

minor_cnt = 32;

break;

default:

minor_offset = 128;

minor_cnt = 64;

break;

}

#endif

定义minor_offset和minor_cnt。

/* Pick a device node number */

mutex_lock(&videodev_lock);

nr = devnode_find(vdev, nr == -1 ? 0 : nr, minor_cnt);

if (nr == minor_cnt)

nr = devnode_find(vdev, 0, minor_cnt);

if (nr == minor_cnt) {

printk(KERN_ERR "could not get a free device nodenumber\n");

mutex_unlock(&videodev_lock);

return -ENFILE;

}

注册device node number。

函数devnode_find：发现节点号。

#ifdefCONFIG_VIDEO_FIXED_MINOR_RANGES

/* 1-on-1 mapping of device node number to minor number */

i = nr;

#else

/* The device node number and minor numbers are independent,so

we just find thefirst free minor number. */

for (i = 0; i < VIDEO_NUM_DEVICES;i++)

if (video_device[i] == NULL)

break;

if (i == VIDEO_NUM_DEVICES) {

mutex_unlock(&videodev_lock);

printk(KERN_ERR "could not get a freeminor\n");

return -ENFILE;

}

#endif

vdev->minor = i + minor_offset;

vdev->num = nr;

devnode_set(vdev);

/* Should not happen since we thought this minor was free */

WARN_ON(video_device[vdev->minor] != NULL);

vdev->index = get_index(vdev);

mutex_unlock(&videodev_lock);

/* if no lock was passed, then make sure the LOCK_ALL_FOPS bit is

clear and warn if itwasn't. */

if (vdev->lock == NULL)

WARN_ON(test_and_clear_bit(V4L2_FL_LOCK_ALL_FOPS, &vdev->flags));

if(vdev->ioctl_ops)

determine_valid_ioctls(vdev);

我都搞晕了，不知道第二部分在搞什么。

第三部分：初始化字符设备

/* Part 3: Initialize thecharacter device */

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;

}

调用cdev_add注册字符设备。这个看的比较简单。

第四部分：

注册device

/* Part 4: register thedevice with sysfs */

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);

if (ret < 0) {

printk(KERN_ERR "%s: device_registerfailed\n", __func__);

goto cleanup;

}

在sysfs中注册device。

/* Register the release callback that will be called when thelast

reference to thedevice goes away. */

vdev->dev.release = v4l2_device_release;

注册回调函数release。

if (nr != -1 && nr != vdev->num &&warn_if_nr_in_use)

printk(KERN_WARNING "%s: requested %s%d, got%s\n", __func__,

name_base, nr, video_device_node_name(vdev));

/* Increase v4l2_devicerefcount */

if(vdev->v4l2_dev)

v4l2_device_get(vdev->v4l2_dev);

第五部分：

在定义了CONFIG_MEDIA_CONTROLLER后才有第五部分，注册entity(实体？)

#ifdefined(CONFIG_MEDIA_CONTROLLER)

/* Part 5: Register the entity. */

if (vdev->v4l2_dev&& vdev->v4l2_dev->mdev&&

vdev->vfl_type !=VFL_TYPE_SUBDEV) {

vdev->entity.type = MEDIA_ENT_T_DEVNODE_V4L;

vdev->entity.name = vdev->name;

vdev->entity.info.v4l.major = VIDEO_MAJOR;

vdev->entity.info.v4l.minor = vdev->minor;

ret = media_device_register_entity(vdev->v4l2_dev->mdev,

&vdev->entity);

if (ret < 0)

printk(KERN_WARNING

"%s: media_device_register_entity failed\n",

__func__);

}

#endif

第六部分：

/* Part 6: Activate thisminor. The char device can now be used.*/

set_bit(V4L2_FL_REGISTERED, &vdev->flags);

mutex_lock(&videodev_lock);

video_device[vdev->minor] = vdev;

mutex_unlock(&videodev_lock);

解锁，激活这一字符设备。

最后：

cleanup:

mutex_lock(&videodev_lock);

if (vdev->cdev)

cdev_del(vdev->cdev);

devnode_clear(vdev);

mutex_unlock(&videodev_lock);

/* Mark this video device as never having been registered. */

vdev->minor = -1;

return ret;