标签:gem info ide handler lease char flag mapping 主设备号
在V4l2初识(一)中,我们已经知道当插上一个摄像头的时候,在uvc_driver.c中最终会调用函数video_register_device函数。接下来我们就简要分析这个函数做了哪些事情,揭开其神秘面纱。
参考原文:https://blog.csdn.net/leesagacious/article/details/49948163
/* 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. */
/*注册video_device,注意如果注册失败,video_device结构体中的release函数不会被调用, 调用者负责释放所有的数据,通常是调用video_device_release()函数来释放*/
static inline int video_register_device(struct video_device *vdev,int type, int nr)
{
return __video_register_device(vdev, type, nr, 1, vdev->fops->owner);
}
参数一:video_devide ------即我们想要注册的video_device结构体
参数二:type-----------要注册的device类型,其中包括:
define VFL_TYPE_GRABBER 0 图像采集设备,包括阿摄像头、调谐器
define VFL_TYPE_VBI1 1 从视频消隐的时间段取得信息的设备(1)
#define VFL_TYPE_RADIO 2 无线电设备
#define VFL_TYPE_SUBDEV 3 视频传播设备
#define VFL_TYPE_MAX 4
参数三:int nr------------device node number
0 == /dev/video 0 1 == /dev/video1 ........ -1 == first free
int __video_register_device(struct video_device *vdev, int type, int nr,
int warn_if_nr_in_use, struct module *owner)
{
int i = 0;
int ret;
int minor_offset = 0; //minor = i+minor_offset
int minor_cnt = VIDEO_NUM_DEVICES; //用于设备节点序号
const char *name_base; //设备的名称会根据传入的type来选择
/* A minor value of -1 marks this video device as never having been registered
次设备号为-1,表明这个设备还没有被注册 */
vdev->minor = -1;
/* the release callback MUST be present
video_device一定要设置release函数,否则要出错返回*/
if (WARN_ON(!vdev->release))
return -EINVAL;
/* v4l2_fh support */
spin_lock_init(&vdev->fh_lock); //获取自旋锁
INIT_LIST_HEAD(&vdev->fh_list); //初始化链表头
/* Part 1: check device type
根据传入的类型type,来选择设备的名称。后面会调用函数dev_set_name(&vdev->dev, "%s%d", name_base, vdev->num)来设置设备的名称
*/
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;
}
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)
/*在app应用程序中,可以通过Ioctl来设置、获得亮度等信息。那么驱动程序谁来接收/存储/ 设置到硬件,或从硬件中获得这些信息?
在驱动程序里面抽象出一个结构体V4L2_ctrl。
那么谁来管理v4l2_ctrl呢?
是利用v4l2_ctrl_handler进行管理的,它像链表一样,里面需要填充各个属 性,也可理解为设置各个属性。
在注册video_device之前的vivi_create_instance()函数中,
初始化v4l2_ctrl_handler
v4l2_ctrl_handler_init(hdl, 11);
创建v4l2_ctrl 并放入到v4l2_ctrl_handler链表
v4l2_ctrl_new_std()
v4l2_ctrl_new_custom()
dev->v4l2_dev.ctrl_handler = hdl; //dev->v4l2_dev : v4l2_device 每一个v4l2设备都用这个结构来描述
下面的代码是将v4l2_ctrl_handler与video_device进行了关联
*/
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;
}
/* Part 2: find a free minor, device node number and device index. */
#ifdef CONFIG_VIDEO_FIXED_MINOR_RANGES
/* Keep the ranges for the first four types for historical
* reasons.
* Newer devices (not yet in place) should use the range
* of 128-191 and just pick the first free minor there
* (new style).
根据传入的类型type,为选择次设备号、设备节点序号作准备。可见可见次设备号是分段使用的
minor = i + minor_offset
*/
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
/* Pick a device node number */
mutex_lock(&videodev_lock); //获取互斥锁
/*获取一个没有被使用的设备节点序号。如果上面传入的是-1,VFL_TYPE_GRABBER,它会从0-64中选择*/
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 node number\n");
mutex_unlock(&videodev_lock);
return -ENFILE;
}
#ifdef CONFIG_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 the first free minor number.
static struct video_device *video_device[256]; 从video_device[]数组中选择一个空缺项,这个空缺项的索引值放到i中
为下面把video_device放入到video_device[i]中做准备,这个设计和registered_fb[]设计的类似
*/
for (i = 0; i < VIDEO_NUM_DEVICES; i++)
if (video_device[i] == NULL)
break;
//检查i的值有没有超过256,否则出错返回
if (i == VIDEO_NUM_DEVICES) {
mutex_unlock(&videodev_lock);
printk(KERN_ERR "could not get a free minor\n");
return -ENFILE;
}
#endif
/*设备的次设备号*/
vdev->minor = i + minor_offset;
vdev->num = nr;
devnode_set(vdev);
/* Should not happen since we thought this minor was free
再一次测试这个video_device[i]是否是空缺项*/
WARN_ON(video_device[vdev->minor] != NULL);
vdev->index = get_index(vdev);
mutex_unlock(&videodev_lock); //释放互斥锁
/* Part 3: Initialize the character device
分配cdev结构体 cdev代表了字符设备的通用信息,通常被嵌入在一个更大的结构体中*/
vdev->cdev = cdev_alloc();
if (vdev->cdev == NULL) {
ret = -ENOMEM;
goto cleanup;
}
/*设置file_operations为v4l2_fops
用户层调用open、mmap、ioctl、read...的时候,这个v4l2_fops中的对应的方法会响应。
如 : 用户层调用mmap(),那么v4l2_fops中的v4l2_mmap()会被调用。
在v4l2_mmap()中,会调用具体设备提供的mmap函数
static int v4l2_mmap(struct file *filp, struct vm_area_struct *vm)
{
....
ret = vdev->fops->mmap(filp, vm);
....
}
*/
vdev->cdev->ops = &v4l2_fops;
vdev->cdev->owner = owner;
/*添加字符设备到系统*/
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;
}
/* Part 4: register the device with sysfs
填充video_device中的成员值 设置video_device所属的类,会在/sys/class/下创建目录*/
vdev->dev.class = &video_class;
/*通过主设备号和次设备号生成dev_t,表示的是一个设备号*/
vdev->dev.devt = MKDEV(VIDEO_MAJOR, vdev->minor);
if (vdev->parent)
vdev->dev.parent = vdev->parent;
/*设置设备的名称*/
dev_set_name(&vdev->dev, "%s%d", name_base, vdev->num);
/*利用device_register,注册字符设备驱动。这个地方和我们写的字符设备驱动程序是一样的*/
ret = device_register(&vdev->dev);
if (ret < 0) {
printk(KERN_ERR "%s: device_register failed\n", __func__);
goto cleanup;
}
/* Register the release callback that will be called when the last reference to the device goes away. */
vdev->dev.release = v4l2_device_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_device refcount */
if (vdev->v4l2_dev)
v4l2_device_get(vdev->v4l2_dev);
#if defined(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
/* Part 6: Activate this minor. The char device can now be used. */
/*将这个unsigned long flags 的第0 位 置1,表示这个video_device 是注册过的了,
在其他位置,会调用video_is_registeried( ) 来判断,其依据 还是测试这个flags的第0位。
video_is_registered( )
{
test_bit( V4L2_FL_REGISTERED, &vdev->flags )
}
*/
//获取锁 ---- 访问临界区 -----释放锁
set_bit(V4L2_FL_REGISTERED, &vdev->flags);
mutex_lock(&videodev_lock);
/*依据次设备号为下标,将设置好的video_device放入到video_device[]中,其他函数会依据次设备号从这个数组中获取对应的video_device,这个和registered_fb[]设计的类似 static struct video_device*video_device[256];*/
video_device[vdev->minor] = vdev;
mutex_unlock(&videodev_lock);
return 0;
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;
}
EXPORT_SYMBOL(__video_register_device);
V4l2初识(二)-----------浅析video_register_device
标签:gem info ide handler lease char flag mapping 主设备号
原文地址:https://www.cnblogs.com/-glb/p/10292768.html