v4l2
一.以vivi.c为例，分析v4l2流程：
a.分配video_device结构体 b.设置 c.注册： video_register_device（）；
1.分配:
vfd = video_device_alloc();
if (!vfd)
goto unreg_dev;
2.设置：
/*************************control设置**************************/
dev->volume = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
V4L2_CID_AUDIO_VOLUME, 0, 255, 1, 200);
dev->brightness = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops, //亮度信息设置，最大最小值等
V4L2_CID_BRIGHTNESS, 0, 255, 1, 127);
dev->contrast = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
V4L2_CID_CONTRAST, 0, 255, 1, 16);
dev->saturation = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
V4L2_CID_SATURATION, 0, 255, 1, 127);
dev->hue = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
V4L2_CID_HUE, -128, 127, 1, 0);
dev->autogain = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
V4L2_CID_AUTOGAIN, 0, 1, 1, 1);
dev->gain = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,
V4L2_CID_GAIN, 0, 255, 1, 100);
dev->button = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_button, NULL);
dev->int32 = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_int32, NULL);
dev->int64 = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_int64, NULL);
dev->boolean = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_boolean, NULL);
dev->menu = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_menu, NULL);
dev->string = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_string, NULL);
dev->bitmask = v4l2_ctrl_new_custom(hdl, &vivi_ctrl_bitmask, NULL);
dev->v4l2_dev.ctrl_handler = hdl
vfd->v4l2_dev = &dev->v4l2_dev;
*vfd = vivi_template;
vfd->debug = debug;
3.注册：
ret = video_register_device(vfd, VFL_TYPE_GRABBER, video_nr);static struct video_device vivi_template = {
.name = "vivi",
.fops = &vivi_fops,
.ioctl_ops = &vivi_ioctl_ops,
.release = video_device_release,
.tvnorms = V4L2_STD_525_60,
.current_norm = V4L2_STD_NTSC_M,
};static const struct v4l2_file_operations vivi_fops = {
.owner = THIS_MODULE,
.open = v4l2_fh_open,
.release = vivi_close,
.read = vivi_read,
.poll = vivi_poll,
.unlocked_ioctl = video_ioctl2, /* 最终调用的是上面的 vivi_ioctl_ops*/
.mmap = vivi_mmap,
};
static const struct v4l2_ioctl_ops vivi_ioctl_ops = {
.vidioc_querycap = vidioc_querycap,
.vidioc_enum_fmt_vid_cap = vidioc_enum_fmt_vid_cap,
.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_s_std = vidioc_s_std,
.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_log_status = v4l2_ctrl_log_status,
.vidioc_subscribe_event = v4l2_ctrl_subscribe_event,
.vidioc_unsubscribe_event = v4l2_event_unsubscribe,
};
分析video_ioctl2
long video_ioctl2(struct file *file,
unsigned int cmd, unsigned long arg)
{
return video_usercopy(file, cmd, arg, __video_do_ioctl);
}
static long __video_do_ioctl(struct file *file,
unsigned int cmd, void *arg)
{
struct video_device *vfd = video_devdata(file); //以此设备号找到video_device
const struct v4l2_ioctl_ops *ops = vfd->ioctl_ops; //调用ioctl_ops
........
switch (cmd) {
case VIDIOC_QUERYCAP:{ }
case VIDIOC_G_PRIORITY:{ }
case VIDIOC_S_PRIORITY:{ }
case VIDIOC_ENUM_FMT:{ }
.......
case VIDIOC_QUERYCTRL:
{struct v4l2_queryctrl *p = arg;
if (vfh && vfh->ctrl_handler)
ret = v4l2_queryctrl(vfh->ctrl_handler,p} //获取前面设置的control信息
}二.在v4l2-dev.c中
int __video_register_device(struct video_device *vdev, int type, int nr,
int warn_if_nr_in_use, struct module *owner)
{
vdev->cdev = cdev_alloc();
vdev->cdev->ops = &v4l2_fops;
vdev->cdev->owner = owner;
ret = cdev_add(vdev->cdev, MKDEV(VIDEO_MAJOR, vdev->minor), 1); //VIDEO_MAJOR=81
video_device[vdev->minor] = vdev;//以次设备号，存入该结构体中
}
static const struct file_operations v4l2_fops = {
.owner = THIS_MODULE,
.read = v4l2_read,
.write = v4l2_write,
.open = v4l2_open,
.get_unmapped_area = v4l2_get_unmapped_area,
.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,
};
分析open,write以及ioctl函数
static int v4l2_open(struct inode *inode, struct file *filp)
{
struct video_device *vdev;
int ret = 0;
/* Check if the video device is available */
mutex_lock(&videodev_lock);
vdev = video_devdata(filp); //以次设备号找到相应的device
/* return ENODEV if the video device has already been removed. */
if (vdev == NULL || !video_is_registered(vdev)) {
mutex_unlock(&videodev_lock);
return -ENODEV;
}
/* and increase the device refcount */
video_get(vdev);
mutex_unlock(&videodev_lock);
if (vdev->fops->open) { //如果device提供了open函数则调用device的open函数
if (vdev->lock && mutex_lock_interruptible(vdev->lock)) {
ret = -ERESTARTSYS;
goto err;
}
if (video_is_registered(vdev))
ret = vdev->fops->open(filp);
else
ret = -ENODEV;
if (vdev->lock)
mutex_unlock(vdev->lock);
}
}对与read，ioctl等函数也一样，以次设备号为基准查找，如果device提供了相应的函数，则调用device的函数（即前面vivi_fops中提供的open 等函数）
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;
}
三.分析ioctl
摄像头驱动程序必需的11个ioctl:
// 表示它是一个摄像头设备
.vidioc_querycap = vidioc_querycap,
/* 用于列举、获得、测试、设置摄像头的数据的格式 */
.vidioc_enum_fmt_vid_cap = vidioc_enum_fmt_vid_cap,
.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,
/* 缓冲区操作: 申请/查询/放入队列/取出队列 */
.vidioc_reqbufs = vidioc_reqbufs,
.vidioc_querybuf = vidioc_querybuf,
.vidioc_qbuf = vidioc_qbuf,
.vidioc_dqbuf = vidioc_dqbuf,
// 启动/停止
.vidioc_streamon = vidioc_streamon,
.vidioc_streamoff = vidioc_streamoff,
四.分析数据获取的过程：
1. 请求分配缓冲区: ioctl(4, VIDIOC_REQBUFS // 请求系统分配缓冲区
videobuf_reqbufs(队列, v4l2_requestbuffers) // 队列在open函数用videobuf_queue_vmalloc_init初始化
// 注意：这个IOCTL只是分配缓冲区的头部信息，真正的缓存还没有分配呢
2. 查询映射缓冲区:
ioctl(4, VIDIOC_QUERYBUF // 查询所分配的缓冲区
videobuf_querybuf // 获得缓冲区的数据格式、大小、每一行长度、高度
mmap(参数里有"大小") // 在这里才分配缓存
v4l2_mmap
vivi_mmap
videobuf_mmap_mapper
videobuf-vmalloc.c里的__videobuf_mmap_mapper
mem->vmalloc = vmalloc_user(pages); // 在这里才给缓冲区分配空间
3. 把缓冲区放入队列:
ioctl(4, VIDIOC_QBUF // 把缓冲区放入队列
videobuf_qbuf
q->ops->buf_prepare(q, buf, field); // 调用驱动程序提供的函数做些预处理
list_add_tail(&buf->stream, &q->stream); // 把缓冲区放入队列的尾部
q->ops->buf_queue(q, buf); // 调用驱动程序提供的"入队列函数"
4. 启动摄像头
ioctl(4, VIDIOC_STREAMON
videobuf_streamon
q->streaming = 1;
5. 用select查询是否有数据
// 驱动程序里必定有: 产生数据、唤醒进程
v4l2_poll
vdev->fops->poll
vivi_poll
videobuf_poll_stream
// 从队列的头部获得缓冲区
buf = list_entry(q->stream.next, struct videobuf_buffer, stream);
// 如果没有数据则休眠
poll_wait(file, &buf->done, wait);
谁来产生数据、谁来唤醒它？
内核线程vivi_thread每30MS执行一次，它调用
vivi_thread_tick
vivi_fillbuff(fh, buf); // 构造数据
wake_up(&buf->vb.done); // 唤醒进程
6. 有数据后从队列里取出缓冲区
// 有那么多缓冲区，APP如何知道哪一个缓冲区有数据？调用VIDIOC_DQBUF
ioctl(4, VIDIOC_DQBUF
vidioc_dqbuf
// 在队列里获得有数据的缓冲区
retval = stream_next_buffer(q, &buf, nonblocking);
// 把它从队列中删掉
list_del(&buf->stream);
// 把这个缓冲区的状态返回给APP
videobuf_status(q, b, buf, q->type);
7. 应用程序根据VIDIOC_DQBUF所得到缓冲区状态，知道是哪一个缓冲区有数据
就去读对应的地址(该地址来自前面的mmap)