V4L2框架分析

——————/

uvc_probe	//uvc_driver.c硬體相關層，定會分配設定向核心層註冊一結構體

v4l2_device_register
uvc_register_chains
uvc_register_terms
uvc_register_video
struct video_device *vdev=video_device_alloc();
vdev->fops = &uvc_fops;
video_register_device(vdev，…… //核心v4l2_dev.c
static const struct file_operations v4l2_fops =
——————/vivi_init

vivi_create_instance
v4l2_device_register //初始化
//struct vivi_dev *dev; struct v4l2_ctrl*volume;
dev->volume = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops, //新增新的標準ctrl
v4l2_cid_audio_volume, 0, 255, 1, 200); //id，最小最大預設
…………
dev->button =v4l2_ctrl_new_custom(hdl, &vivi_ctrl_button, null);
…………
struct video_device *vfd=video_device_alloc；//分配
*vfd = vivi_template; //設定
vfd->v4l2_dev = &dev->v4l2_dev;
video_register_device(struct video_device *vdev,int type, int nr) //註冊
__video_register_device
switch (type) ;
static const struct v4l2_file_operations vivi_fops = ;

——————/分析讀寫過程

v4l2_open

struct video_device *vdev = video_devdata(filp);

//據次…從陣列中得到video_device結構體

return video_device[iminor(file->f_path.dentry->d_inode)];

if (vdev->fops->open)

……//若存在則呼叫，實際呼叫v4l2_file_operations的v4l2_fh_open

read、write過程同上

——————/

v4l2_ioctl

struct video_device *vdev = video_devdata(filp);

if (vdev->fops->unlocked_ioctl)

vdev->fops->unlocked_ioctl(filp, cmd, arg);

video_ioctl2

return video_usercopy(file, cmd, arg, __video_do_ioctl);

__video_do_ioctl(struct file *file,unsigned int cmd, void *arg)

struct video_device *vfd = video_devdata(file);

switch (cmd)

case vidioc_querycap:

……——————/

怎麼寫v4l2驅動？

① 分配/設定/註冊v4l2_device結構：v4l2_device_register

② 分配video_device：video_device_alloc

設定（包含v4l2_device指標，使其指向①所分配設定的）

註冊——————/

vivi_create_instance

struct video_device *vfd;
struct vivi_dev *dev;
struct v4l2_ctrl_handler *hdl;
hdl = &dev->ctrl_handler;
v4l2_ctrl_handler_init(hdl, 11); //初始化ctrl_handler
dev->brightness = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,v4l2_cid_brightness, 0, 255, 1, 127); 
dev->volume = v4l2_ctrl_new_std(hdl, &vivi_ctrl_ops,v4l2_cid_audio_volume, 0, 255, 1, 200);
…………
//handler含煉表頭，用v4l2_ctrl_new_std、v4l2_ctrl_new_custom向其新增v4l2_ctrl（屬性）
dev->v4l2_dev.ctrl_handler = hdl; //與v4l2_device關聯
vfd->v4l2_dev = &dev->v4l2_dev;
__video_register_device開頭
struct video_device *vdev；
if (vdev->ctrl_handler == null)
vdev->ctrl_handler = vdev->v4l2_dev->ctrl_handler;
static const struct v4l2_ioctl_ops vivi_ioctl_ops = ;

__video_do_ioctl

struct video_device *vfd = video_devdata(file);
const struct v4l2_ioctl_ops *ops = vfd->ioctl_ops;
switch (cmd)
case vidioc_querycap:
ops->vidioc_querycap(file, fh, cap); //部分情況直接呼叫
……case vidioc_queryctrl:
if (vfd->ctrl_handler)
ret = v4l2_queryctrl(vfd->ctrl_handler, p);
struct v4l2_ctrl *ctrl;
struct v4l2_ctrl_ref *ref;
ref = find_ref(hdl, id); //據id從v4l2_ctrl_handler找到v4l2_ctrl
ctrl = ref->ctrl;
qc->minimum = ctrl->minimum; //返回其最小最大值預設值
qc->maximum = ctrl->maximum;

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