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发布: [02-4]_videobuffer2的3个ops, [02-5]_videobuffer2情景分析

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2023-08-26 11:07:02 +08:00
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347
IMX6ULL/doc_pic/13_V4L2/02_V4L2驱动程序框架.md
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@@ -142,7 +142,7 @@ APP操作buffer的示意图如下：
#### 1.3.2 三类操作结构体
#### 1.3.2 videobuffer2的3个ops
V4L2中使用vb2_queue来管理缓冲区，里面有3个操作结构体：
@@ -150,56 +150,101 @@ V4L2中使用vb2_queue来管理缓冲区，里面有3个操作结构体：
这3个操作结构体的作用为：
* `const struct vb2_ops *ops`：驱动相关的回调函数，通过下面几个宏来调用
* `const struct vb2_buf_ops *buf_ops`：在用户空间、内核空间之间传递buffer信息，通过下面几个宏来调用
![image-20230826003824317](pic/35_call_buf_ops.png)
* `const struct vb2_mem_ops *mem_ops`：分配内存用的回调函数，通过下面几个宏来调用
![image-20230826004001342](pic/36_call_mem_ops.png)
* `const struct vb2_ops *ops`：硬件相关的回调函数，通过下面几个宏来调用
![image-20230816184848876](pic/32_call_vbs_ops.png)
* `const struct vb2_mem_ops *mem_ops`：分配内存用的回调函数
* `const struct vb2_buf_ops *buf_ops`：在用户空间、内核空间之间传递buffer信息
#### 1.3.3 vb2_ops
这3个ops的层次图如下：
`struct vb2_ops`示例如下：
![image-20230826003154388](pic/37_three_ops.png)
![image-20230816171236918](pic/31_vbs_ops_example.png)
完整的注册流程(参考`drivers\media\usb\airspy\airspy.c`)：
```shell
static struct video_device airspy_template = {
.name = "AirSpy SDR",
.release = video_device_release_empty,
.fops = &airspy_fops,
.ioctl_ops = &airspy_ioctl_ops,
};
/* 构造一个vb2_queue */
/* Init videobuf2 queue structure */
s->vb_queue.type = V4L2_BUF_TYPE_SDR_CAPTURE;
s->vb_queue.io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ;
s->vb_queue.drv_priv = s;
s->vb_queue.buf_struct_size = sizeof(struct airspy_frame_buf);
s->vb_queue.ops = &airspy_vb2_ops; // vb2_ops, 硬件相关的操作函数
s->vb_queue.mem_ops = &vb2_vmalloc_memops; // vb2_mem_ops, 辅助结构体,用于mem ops(alloc、mmap)
s->vb_queue.timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
ret = vb2_queue_init(&s->vb_queue);
q->buf_ops = &v4l2_buf_ops; // vb2_buf_ops, 用于APP和驱动传递参数
// 分配/设置video_device结构体
s->vdev = airspy_template;
s->vdev.queue = &s->vb_queue; // 指向前面构造的vb2_queue
// 初始化一个v4l2_device结构体(起辅助作用)
/* Register the v4l2_device structure */
s->v4l2_dev.release = airspy_video_release;
ret = v4l2_device_register(&intf->dev, &s->v4l2_dev);
// video_device和4l2_device建立联系
s->vdev.v4l2_dev = &s->v4l2_dev;
// 注册video_device结构体
ret = video_register_device(&s->vdev, VFL_TYPE_SDR, -1);
__video_register_device
// 根据次设备号把video_device结构体放入数组
video_device[vdev->minor] = vdev;
// 注册字符设备驱动程序
vdev->cdev->ops = &v4l2_fops;
vdev->cdev->owner = owner;
ret = cdev_add(vdev->cdev, MKDEV(VIDEO_MAJOR, vdev->minor), 1);
```
#### 1.3.3 vb2_buf_ops
`struct vb2_buf_ops`示例如下：
![image-20230818151510055](pic/34_vb2_buf_ops_example.png)
原型如下：
```c
struct vb2_ops {
int (*queue_setup)(struct vb2_queue *q,
unsigned int *num_buffers, unsigned int *num_planes,
unsigned int sizes[], struct device *alloc_devs[]);
void (*wait_prepare)(struct vb2_queue *q);
void (*wait_finish)(struct vb2_queue *q);
int (*buf_init)(struct vb2_buffer *vb);
int (*buf_prepare)(struct vb2_buffer *vb);
void (*buf_finish)(struct vb2_buffer *vb);
void (*buf_cleanup)(struct vb2_buffer *vb);
int (*start_streaming)(struct vb2_queue *q, unsigned int count);
void (*stop_streaming)(struct vb2_queue *q);
void (*buf_queue)(struct vb2_buffer *vb);
struct vb2_buf_ops {
int (*verify_planes_array)(struct vb2_buffer *vb, const void *pb);
void (*fill_user_buffer)(struct vb2_buffer *vb, void *pb);
int (*fill_vb2_buffer)(struct vb2_buffer *vb, const void *pb,
struct vb2_plane *planes);
void (*copy_timestamp)(struct vb2_buffer *vb, const void *pb);
};
```
各成员的作用为：
| vb2_ops结构体成员 | 作用 |
| ----------------- | ------------------------------------------------------------ |
| queue_setup | APP调用ioctl VIDIOC_REQBUFS或VIDIOC_CREATE_BUFS时，<br />驱动程序在分配内存之前，会调用此函数。<br />作用：通过它来询问驱动程序"你需要多少个buffer？每个buffer需要多少个plane？"<br />这个函数被调用2次：第1次用来表明驱动程序对buffer的需求，但是不一定能全部分配这些buffer，当分配出buffer后，再调用第2次以验证"这些buffer是否足够"。 |
| wait_prepare | 释放驱动自己的互斥锁 |
| wait_finish | 申请驱动自己的互斥锁 |
| buf_init | 分配vb2_buffer及它内部存储数据的buffer后，使用buf_init进行驱动相关的初始化 |
| buf_prepare | APP调用ioctl VIDIOC_QBUF或VIDIOC_PREPARE_BUF时，驱动程序会在执行硬件操作前，调用此函数进行必要的初始化。 |
| buf_finish | APP调用ioctl VIDIOC_DQBUF后，在驱动程序返回用户空间之前，会调用此函数，可以在这个函数里修改buffer。或者驱动程序内部停止或暂停streaming时，也会调用此函数。 |
| buf_cleanup | 在buffer被释放前调用，驱动程序在这个函数里执行额外的清除工作。 |
| start_streaming | 驱动相关的"启动streaming"函数 |
| stop_streaming | 驱动相关的"停止streaming"函数 |
| buf_queue | 把buffer传送给驱动，驱动获得数据、填充好buffer后会调用vb2_buffer_done函数返还buffer。 |
| vb2_buf_ops结构体成员 | 作用 |
| --------------------- | ------------------------------------------------------------ |
| verify_planes_array | APP调用ioctl VIDIOC_DQBUF时，在驱动内部会调用此函数，用来验证这个buffer含有足够多的plane。 |
| fill_user_buffer | 使用驱动的vb2_buffer结构体来填充一个v4l2_buffer结构体，用来给用户空间提供更多信息。APP调用ioctl VIDIOC_QUERYBUF、VIDIOC_PREPARE_BUF、VIDIOC_QBUF、VIDIOC_DQBUF时，都会传入一个v4l2_buffer结构体。 |
| fill_vb2_buffer | APP调用ioctl VIDIOC_QBUF时，传入一个v4l2_buffer结构体，驱动里会用它来填充vb2_buffer结构体。 |
| copy_timestamp | APP调用ioctl VIDIOC_QBUF时，传入一个v4l2_buffer结构体，用户程序可以在它的timestamp里记下时间。驱动程序可以调用此函数把timestamp写入vb2_buffer.timestamp里。 |
@@ -251,7 +296,7 @@ struct vb2_mem_ops {
| --------------------- | ------------------------------------------------------------ |
| alloc | 分配真正用于存储视频数据的buffer，可能还分配私有数据 |
| put | 通知分配器：这块buffer不再使用了。通常会释放内存。 |
| get_dmabuf | 申请驱动自己的互斥锁 |
| get_dmabuf | 获得DMA BUF给底层驱动使用 |
| get_userptr | 如果存储视频数据的buffer是userptr（由APP提供），那么APP调用ioctl VIDIOC_QBUF时，需要传入APP的buffer指针。驱动程序内部通过此函数把用户空间的buffer映射到内核空间。 |
| put_userptr | 通知分配器：这块USERPTR缓冲区不再使用 |
| attach_dmabuf | 如果存储视频数据的buffer是DMA Buf，那么在把这个buffer放入队列前会调用此函数：记录这个DMA Buf。 |
@@ -267,82 +312,198 @@ struct vb2_mem_ops {
#### 1.3.5 vb2_buf_ops
`struct vb2_buf_ops`示例如下：
![image-20230818151510055](pic/34_vb2_buf_ops_example.png)
#### 1.3.5 vb2_ops
`struct vb2_ops`示例如下：
![image-20230816171236918](pic/31_vbs_ops_example.png)
原型如下：
```c
struct vb2_buf_ops {
int (*verify_planes_array)(struct vb2_buffer *vb, const void *pb);
void (*fill_user_buffer)(struct vb2_buffer *vb, void *pb);
int (*fill_vb2_buffer)(struct vb2_buffer *vb, const void *pb,
struct vb2_plane *planes);
void (*copy_timestamp)(struct vb2_buffer *vb, const void *pb);
struct vb2_ops {
int (*queue_setup)(struct vb2_queue *q,
unsigned int *num_buffers, unsigned int *num_planes,
unsigned int sizes[], struct device *alloc_devs[]);
void (*wait_prepare)(struct vb2_queue *q);
void (*wait_finish)(struct vb2_queue *q);
int (*buf_init)(struct vb2_buffer *vb);
int (*buf_prepare)(struct vb2_buffer *vb);
void (*buf_finish)(struct vb2_buffer *vb);
void (*buf_cleanup)(struct vb2_buffer *vb);
int (*start_streaming)(struct vb2_queue *q, unsigned int count);
void (*stop_streaming)(struct vb2_queue *q);
void (*buf_queue)(struct vb2_buffer *vb);
};
```
各成员的作用为：
| vb2_buf_ops结构体成员 | 作用 |
| --------------------- | ------------------------------------------------------------ |
| verify_planes_array | APP调用ioctl VIDIOC_DQBUF时，在驱动内部会调用此函数，用来验证这个buffer含有足够多的plane。 |
| fill_user_buffer | 使用驱动的vb2_buffer结构体来填充一个v4l2_buffer结构体，用来给用户空间提供更多信息。APP调用ioctl VIDIOC_QUERYBUF、VIDIOC_PREPARE_BUF、VIDIOC_QBUF、VIDIOC_DQBUF时，都会传入一个v4l2_buffer结构体。 |
| fill_vb2_buffer | APP调用ioctl VIDIOC_QBUF时，传入一个v4l2_buffer结构体，驱动里会用它来填充vb2_buffer结构体。 |
| copy_timestamp | APP调用ioctl VIDIOC_QBUF时，传入一个v4l2_buffer结构体，用户程序可以在它的timestamp里记下时间。驱动程序可以调用此函数把timestamp写入vb2_buffer.timestamp里。 |
| vb2_ops结构体成员 | 作用 |
| ----------------- | ------------------------------------------------------------ |
| queue_setup | APP调用ioctl VIDIOC_REQBUFS或VIDIOC_CREATE_BUFS时，<br />驱动程序在分配内存之前，会调用此函数。<br />作用：通过它来询问硬件驱动"你需要多少个buffer？每个buffer需要多少个plane？"<br />这个函数被调用2次：第1次用来表明驱动程序对buffer的需求，但是不一定能全部分配这些buffer，当分配出buffer后，再调用第2次以验证"这些buffer是否足够"。 |
| wait_prepare | 释放驱动自己的互斥锁 |
| wait_finish | 申请驱动自己的互斥锁 |
| buf_init | 分配vb2_buffer及它内部存储数据的buffer后，使用buf_init进行驱动相关的初始化 |
| buf_prepare | APP调用ioctl VIDIOC_QBUF或VIDIOC_PREPARE_BUF时，驱动程序会在执行硬件操作前，调用此函数进行必要的初始化。 |
| buf_finish | APP调用ioctl VIDIOC_DQBUF后，在驱动程序返回用户空间之前，会调用此函数，可以在这个函数里修改buffer。或者驱动程序内部停止或暂停streaming时，也会调用此函数。 |
| buf_cleanup | 在buffer被释放前调用，驱动程序在这个函数里执行额外的清除工作。 |
| start_streaming | 驱动相关的"启动streaming"函数 |
| stop_streaming | 驱动相关的"停止streaming"函数 |
| buf_queue | 把buffer传送给驱动，驱动获得数据、填充好buffer后会调用vb2_buffer_done函数返还buffer。 |
#### 1.3.6 videobuffer2情景分析
情景分析1：申请buffer
```c
APP ioctl VIDIOC_PREPARE_BUF
APP ioctl VIDIOC_REQBUFS
------------------------------
v4l2_ioctl_ops.vidioc_prepare_buf
vb2_ioctl_prepare_buf
vb2_prepare_buf(vdev->queue, p);
vb2_core_prepare_buf(q, b->index, b);
ret = __buf_prepare(vb, pb);
ret = __qbuf_mmap(vb, pb);
v4l_reqbufs // v4l2-ioctl.c
ops->vidioc_reqbufs(file, fh, p);
vb2_ioctl_reqbufs // videobuf2-v4l2.c
vb2_core_reqbufs
/*
* Ask the driver how many buffers and planes per buffer it requires.
* Driver also sets the size and allocator context for each plane.
*/
/* 调用硬件相关的vb2_ops.queue_setup，确认需要多少个buffer、每个buffer里有多少个plane */
ret = call_qop(q, queue_setup, q, &num_buffers, &num_planes,
plane_sizes, q->alloc_devs);
/* Finally, allocate buffers and video memory */
allocated_buffers =
__vb2_queue_alloc(q, memory, num_buffers, num_planes, plane_sizes);
ret = __vb2_buf_mem_alloc(vb);
// 调用vb2_mem_ops.alloc分配内存
mem_priv = call_ptr_memop(vb, alloc,
q->alloc_devs[plane] ? : q->dev,
q->dma_attrs, size, dma_dir, q->gfp_flags);
/* 驱动想得到M个buffer，但是可能只分配了N个buffer，可以吗？问驱动
* 再次调用硬件相关的vb2_ops.queue_setup，确认已经分配的buffer个数、每个buffer的plane个数是否符合硬件需求
*/
ret = call_qop(q, queue_setup, q, &num_buffers,
&num_planes, plane_sizes, q->alloc_devs);
```
情景分析2：把buffer放入队列
```c
APP ioctl VIDIOC_QBUF
------------------------------
v4l_qbuf // v4l2-ioctl.c
ops->vidioc_qbuf(file, fh, p);
vb2_ioctl_qbuf // videobuf2-v4l2.c
vb2_qbuf(vdev->queue, p); // videobuf2-v4l2.c
vb2_core_qbuf(q, b->index, b); // videobuf2-core.c
ret = __buf_prepare(vb, pb);
ret = __qbuf_mmap(vb, pb); // videobuf2-core.c
if (pb) // 调用vb2_buf_ops.fill_vb2_buffer, 使用APP传入的v4l2_buffer来设置驱动的vb2_buffer
ret = call_bufop(vb->vb2_queue, fill_vb2_buffer,
vb, pb, vb->planes);
// 硬件相关的vb2_ops.buf_prepare, 对buffer做些准备工作
return ret ? ret : call_vb_qop(vb, buf_prepare, vb);
// 把buffer放入空闲链表
list_add_tail(&vb->queued_entry, &q->queued_list);
if (pb) // 调用vb2_buf_ops.copy_timestamp, 使用APP传入的v4l2_buffer来设置驱动的vb2_buffer
call_void_bufop(q, copy_timestamp, vb, pb);
/*
* If already streaming, give the buffer to driver for processing.
* If not, the buffer will be given to driver on next streamon.
*/
if (q->start_streaming_called)
__enqueue_in_driver(vb);
/* sync buffers */
for (plane = 0; plane < vb->num_planes; ++plane)
// 调用vb2_mem_ops.prepare做准备
call_void_memop(vb, prepare, vb->planes[plane].mem_priv);
// 调用硬件相关的vb2_ops.buf_queue把buffer传送给驱动
call_void_vb_qop(vb, buf_queue, vb);
/* Fill buffer information for the userspace */
if (pb) // 调用vb2_buf_ops.fill_user_buffer, 使用驱动的vb2_buffer为APP设置v4l2_buffer
call_void_bufop(q, fill_user_buffer, vb, pb);
/*
* If streamon has been called, and we haven't yet called
* start_streaming() since not enough buffers were queued, and
* we now have reached the minimum number of queued buffers,
* then we can finally call start_streaming().
*/
if (q->streaming && !q->start_streaming_called &&
q->queued_count >= q->min_buffers_needed) {
ret = vb2_start_streaming(q);
/*
* If any buffers were queued before streamon,
* we can now pass them to driver for processing.
*/
list_for_each_entry(vb, &q->queued_list, queued_entry)
__enqueue_in_driver(vb);
/* sync buffers */
for (plane = 0; plane < vb->num_planes; ++plane)
// 调用vb2_mem_ops.prepare做准备
call_void_memop(vb, prepare, vb->planes[plane].mem_priv);
// 调用硬件相关的vb2_ops.buf_queue把buffer传送给驱动
call_void_vb_qop(vb, buf_queue, vb);
/* Tell the driver to start streaming */
q->start_streaming_called = 1;
// 调用硬件相关的vb2_ops.start_streaming启动硬件传输
ret = call_qop(q, start_streaming, q,
atomic_read(&q->owned_by_drv_count));
```
情景分析3：把buffer取出队列
```shell
APP ioctl VIDIOC_DQBUF
------------------------------
v4l_dqbuf // v4l2-ioctl.c
ops->vidioc_dqbuf(file, fh, p);
vb2_ioctl_dqbuf // videobuf2-v4l2.c
vb2_dqbuf(vdev->queue, p, file->f_flags & O_NONBLOCK);
ret = vb2_core_dqbuf(q, NULL, b, nonblocking);
ret = __vb2_get_done_vb(q, &vb, pb, nonblocking);
ret = __vb2_wait_for_done_vb(q, nonblocking);
call_void_qop(q, wait_prepare, q);
wait_event_interruptible
call_void_qop(q, wait_finish, q);
*vb = list_first_entry(&q->done_list, struct vb2_buffer, done_entry);
if (pb)
ret = call_bufop(vb->vb2_queue, fill_vb2_buffer,
vb, pb, vb->planes);
__fill_vb2_buffer
return ret ? ret : call_vb_qop(vb, buf_prepare, vb);
ret = call_bufop(q, verify_planes_array, *vb, pb);
__verify_planes_array_core
__verify_planes_array(vb, pb);
if (!ret)
list_del(&(*vb)->done_entry);
call_void_vb_qop(vb, buf_finish, vb);
/* Fill buffer information for the userspace */
call_void_bufop(q, fill_user_buffer, vb, pb);
__fill_v4l2_buffer
vb2_core_dqbuf
ret = __vb2_get_done_vb(q, &vb, pb, nonblocking);
ret = __vb2_wait_for_done_vb(q, nonblocking);
call_void_qop(q, wait_prepare, q);
wait_event_interruptible
call_void_qop(q, wait_finish, q);
*vb = list_first_entry(&q->done_list, struct vb2_buffer, done_entry);
if (pb)
ret = call_bufop(q, verify_planes_array, *vb, pb);
__verify_planes_array_core
__verify_planes_array(vb, pb);
if (!ret)
list_del(&(*vb)->done_entry);
call_void_vb_qop(vb, buf_finish, vb);
/* go back to dequeued state */
__vb2_dqbuf(vb);
call_void_memop(vb, unmap_dmabuf, vb->planes[i].mem_priv);
vb2_vmalloc_unmap_dmabuf
dma_buf_vunmap(buf->dbuf, buf->vaddr);
vb2_core_qbuf
if (pb)
call_void_bufop(q, copy_timestamp, vb, pb);
__copy_timestamp
vb->timestamp = timeval_to_ns(&b->timestamp);
/* go back to dequeued state */
__vb2_dqbuf(vb);
call_void_memop(vb, unmap_dmabuf, vb->planes[i].mem_priv);
vb2_vmalloc_unmap_dmabuf
dma_buf_vunmap(buf->dbuf, buf->vaddr);
```

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7
README.md
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@@ -802,6 +802,13 @@ git clone https://e.coding.net/weidongshan/linux/doc_and_source_for_drivers.git
[02-3]_videobuffer2缓冲区结构体
```
* 2023.08.26 发布"摄像头驱动"
```shell
[02-4]_videobuffer2的3个ops
[02-5]_videobuffer2情景分析
```

366
STM32MP157/doc_pic/13_V4L2/02_V4L2驱动程序框架.md
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@@ -142,6 +142,372 @@ APP操作buffer的示意图如下：
#### 1.3.2 videobuffer2的3个ops
V4L2中使用vb2_queue来管理缓冲区，里面有3个操作结构体：
![image-20230816154549808](pic/30_vb2_queue_ops.png)
这3个操作结构体的作用为：
* `const struct vb2_buf_ops *buf_ops`：在用户空间、内核空间之间传递buffer信息，通过下面几个宏来调用
![image-20230826003824317](pic/35_call_buf_ops.png)
* `const struct vb2_mem_ops *mem_ops`：分配内存用的回调函数，通过下面几个宏来调用
![image-20230826004001342](pic/36_call_mem_ops.png)
* `const struct vb2_ops *ops`：硬件相关的回调函数，通过下面几个宏来调用
![image-20230816184848876](pic/32_call_vbs_ops.png)
这3个ops的层次图如下：
![image-20230826003154388](pic/37_three_ops.png)
完整的注册流程(参考`drivers\media\usb\airspy\airspy.c`)：
```shell
static struct video_device airspy_template = {
.name = "AirSpy SDR",
.release = video_device_release_empty,
.fops = &airspy_fops,
.ioctl_ops = &airspy_ioctl_ops,
};
/* 构造一个vb2_queue */
/* Init videobuf2 queue structure */
s->vb_queue.type = V4L2_BUF_TYPE_SDR_CAPTURE;
s->vb_queue.io_modes = VB2_MMAP | VB2_USERPTR | VB2_READ;
s->vb_queue.drv_priv = s;
s->vb_queue.buf_struct_size = sizeof(struct airspy_frame_buf);
s->vb_queue.ops = &airspy_vb2_ops; // vb2_ops, 硬件相关的操作函数
s->vb_queue.mem_ops = &vb2_vmalloc_memops; // vb2_mem_ops, 辅助结构体,用于mem ops(alloc、mmap)
s->vb_queue.timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
ret = vb2_queue_init(&s->vb_queue);
q->buf_ops = &v4l2_buf_ops; // vb2_buf_ops, 用于APP和驱动传递参数
// 分配/设置video_device结构体
s->vdev = airspy_template;
s->vdev.queue = &s->vb_queue; // 指向前面构造的vb2_queue
// 初始化一个v4l2_device结构体(起辅助作用)
/* Register the v4l2_device structure */
s->v4l2_dev.release = airspy_video_release;
ret = v4l2_device_register(&intf->dev, &s->v4l2_dev);
// video_device和4l2_device建立联系
s->vdev.v4l2_dev = &s->v4l2_dev;
// 注册video_device结构体
ret = video_register_device(&s->vdev, VFL_TYPE_SDR, -1);
__video_register_device
// 根据次设备号把video_device结构体放入数组
video_device[vdev->minor] = vdev;
// 注册字符设备驱动程序
vdev->cdev->ops = &v4l2_fops;
vdev->cdev->owner = owner;
ret = cdev_add(vdev->cdev, MKDEV(VIDEO_MAJOR, vdev->minor), 1);
```
#### 1.3.3 vb2_buf_ops
`struct vb2_buf_ops`示例如下：
![image-20230818151510055](pic/34_vb2_buf_ops_example.png)
原型如下：
```c
struct vb2_buf_ops {
int (*verify_planes_array)(struct vb2_buffer *vb, const void *pb);
void (*fill_user_buffer)(struct vb2_buffer *vb, void *pb);
int (*fill_vb2_buffer)(struct vb2_buffer *vb, const void *pb,
struct vb2_plane *planes);
void (*copy_timestamp)(struct vb2_buffer *vb, const void *pb);
};
```
各成员的作用为：
| vb2_buf_ops结构体成员 | 作用 |
| --------------------- | ------------------------------------------------------------ |
| verify_planes_array | APP调用ioctl VIDIOC_DQBUF时，在驱动内部会调用此函数，用来验证这个buffer含有足够多的plane。 |
| fill_user_buffer | 使用驱动的vb2_buffer结构体来填充一个v4l2_buffer结构体，用来给用户空间提供更多信息。APP调用ioctl VIDIOC_QUERYBUF、VIDIOC_PREPARE_BUF、VIDIOC_QBUF、VIDIOC_DQBUF时，都会传入一个v4l2_buffer结构体。 |
| fill_vb2_buffer | APP调用ioctl VIDIOC_QBUF时，传入一个v4l2_buffer结构体，驱动里会用它来填充vb2_buffer结构体。 |
| copy_timestamp | APP调用ioctl VIDIOC_QBUF时，传入一个v4l2_buffer结构体，用户程序可以在它的timestamp里记下时间。驱动程序可以调用此函数把timestamp写入vb2_buffer.timestamp里。 |
#### 1.3.4 vb2_mem_ops
`struct vb2_mem_ops`示例如下：
![image-20230817162952015](pic/33_vb2_mem_ops_example.png)
原型如下：
```c
struct vb2_mem_ops {
void *(*alloc)(struct device *dev, unsigned long attrs,
unsigned long size,
enum dma_data_direction dma_dir,
gfp_t gfp_flags);
void (*put)(void *buf_priv);
struct dma_buf *(*get_dmabuf)(void *buf_priv, unsigned long flags);
void *(*get_userptr)(struct device *dev, unsigned long vaddr,
unsigned long size,
enum dma_data_direction dma_dir);
void (*put_userptr)(void *buf_priv);
void (*prepare)(void *buf_priv);
void (*finish)(void *buf_priv);
void *(*attach_dmabuf)(struct device *dev,
struct dma_buf *dbuf,
unsigned long size,
enum dma_data_direction dma_dir);
void (*detach_dmabuf)(void *buf_priv);
int (*map_dmabuf)(void *buf_priv);
void (*unmap_dmabuf)(void *buf_priv);
void *(*vaddr)(void *buf_priv);
void *(*cookie)(void *buf_priv);
unsigned int (*num_users)(void *buf_priv);
int (*mmap)(void *buf_priv, struct vm_area_struct *vma);
};
```
各成员的作用为：
| vb2_mem_ops结构体成员 | 作用 |
| --------------------- | ------------------------------------------------------------ |
| alloc | 分配真正用于存储视频数据的buffer，可能还分配私有数据 |
| put | 通知分配器：这块buffer不再使用了。通常会释放内存。 |
| get_dmabuf | 获得DMA BUF给底层驱动使用 |
| get_userptr | 如果存储视频数据的buffer是userptr（由APP提供），那么APP调用ioctl VIDIOC_QBUF时，需要传入APP的buffer指针。驱动程序内部通过此函数把用户空间的buffer映射到内核空间。 |
| put_userptr | 通知分配器：这块USERPTR缓冲区不再使用 |
| attach_dmabuf | 如果存储视频数据的buffer是DMA Buf，那么在把这个buffer放入队列前会调用此函数：记录这个DMA Buf。 |
| detach_dmabuf | 不再使用这个DMA Buf时，做些清理工作（比如在attach_dmabuf里分配了数据，就在这里释放掉） |
| map_dmabuf | 把DMA Buf映射到内核空间 |
| unmap_dmabuf | map_dmabuf的反操作 |
| prepare | 每当buffer被从用户空间传递到驱动时，此函数被调用，可以用来做某些同步操作。可选。 |
| finish | 每当buffer被从驱动传递到用户空间时，此函数被调用，可以用来做某些同步操作。可选。 |
| vaddr | 返回这块内存的内核空间地址 |
| cookie | 没什么用 |
| num_users | 返回这块内存的引用计数 |
| mmap | 把这块内存，映射到用户空间 |
#### 1.3.5 vb2_ops
`struct vb2_ops`示例如下：
![image-20230816171236918](pic/31_vbs_ops_example.png)
原型如下：
```c
struct vb2_ops {
int (*queue_setup)(struct vb2_queue *q,
unsigned int *num_buffers, unsigned int *num_planes,
unsigned int sizes[], struct device *alloc_devs[]);
void (*wait_prepare)(struct vb2_queue *q);
void (*wait_finish)(struct vb2_queue *q);
int (*buf_init)(struct vb2_buffer *vb);
int (*buf_prepare)(struct vb2_buffer *vb);
void (*buf_finish)(struct vb2_buffer *vb);
void (*buf_cleanup)(struct vb2_buffer *vb);
int (*start_streaming)(struct vb2_queue *q, unsigned int count);
void (*stop_streaming)(struct vb2_queue *q);
void (*buf_queue)(struct vb2_buffer *vb);
};
```
各成员的作用为：
| vb2_ops结构体成员 | 作用 |
| ----------------- | ------------------------------------------------------------ |
| queue_setup | APP调用ioctl VIDIOC_REQBUFS或VIDIOC_CREATE_BUFS时，<br />驱动程序在分配内存之前，会调用此函数。<br />作用：通过它来询问硬件驱动"你需要多少个buffer？每个buffer需要多少个plane？"<br />这个函数被调用2次：第1次用来表明驱动程序对buffer的需求，但是不一定能全部分配这些buffer，当分配出buffer后，再调用第2次以验证"这些buffer是否足够"。 |
| wait_prepare | 释放驱动自己的互斥锁 |
| wait_finish | 申请驱动自己的互斥锁 |
| buf_init | 分配vb2_buffer及它内部存储数据的buffer后，使用buf_init进行驱动相关的初始化 |
| buf_prepare | APP调用ioctl VIDIOC_QBUF或VIDIOC_PREPARE_BUF时，驱动程序会在执行硬件操作前，调用此函数进行必要的初始化。 |
| buf_finish | APP调用ioctl VIDIOC_DQBUF后，在驱动程序返回用户空间之前，会调用此函数，可以在这个函数里修改buffer。或者驱动程序内部停止或暂停streaming时，也会调用此函数。 |
| buf_cleanup | 在buffer被释放前调用，驱动程序在这个函数里执行额外的清除工作。 |
| start_streaming | 驱动相关的"启动streaming"函数 |
| stop_streaming | 驱动相关的"停止streaming"函数 |
| buf_queue | 把buffer传送给驱动，驱动获得数据、填充好buffer后会调用vb2_buffer_done函数返还buffer。 |
#### 1.3.6 videobuffer2情景分析
情景分析1：申请buffer
```c
APP ioctl VIDIOC_REQBUFS
------------------------------
v4l_reqbufs // v4l2-ioctl.c
ops->vidioc_reqbufs(file, fh, p);
vb2_ioctl_reqbufs // videobuf2-v4l2.c
vb2_core_reqbufs
/*
* Ask the driver how many buffers and planes per buffer it requires.
* Driver also sets the size and allocator context for each plane.
*/
/* 调用硬件相关的vb2_ops.queue_setup，确认需要多少个buffer、每个buffer里有多少个plane */
ret = call_qop(q, queue_setup, q, &num_buffers, &num_planes,
plane_sizes, q->alloc_devs);
/* Finally, allocate buffers and video memory */
allocated_buffers =
__vb2_queue_alloc(q, memory, num_buffers, num_planes, plane_sizes);
ret = __vb2_buf_mem_alloc(vb);
// 调用vb2_mem_ops.alloc分配内存
mem_priv = call_ptr_memop(vb, alloc,
q->alloc_devs[plane] ? : q->dev,
q->dma_attrs, size, dma_dir, q->gfp_flags);
/* 驱动想得到M个buffer，但是可能只分配了N个buffer，可以吗？问驱动
* 再次调用硬件相关的vb2_ops.queue_setup，确认已经分配的buffer个数、每个buffer的plane个数是否符合硬件需求
*/
ret = call_qop(q, queue_setup, q, &num_buffers,
&num_planes, plane_sizes, q->alloc_devs);
```
情景分析2：把buffer放入队列
```c
APP ioctl VIDIOC_QBUF
------------------------------
v4l_qbuf // v4l2-ioctl.c
ops->vidioc_qbuf(file, fh, p);
vb2_ioctl_qbuf // videobuf2-v4l2.c
vb2_qbuf(vdev->queue, p); // videobuf2-v4l2.c
vb2_core_qbuf(q, b->index, b); // videobuf2-core.c
ret = __buf_prepare(vb, pb);
ret = __qbuf_mmap(vb, pb); // videobuf2-core.c
if (pb) // 调用vb2_buf_ops.fill_vb2_buffer, 使用APP传入的v4l2_buffer来设置驱动的vb2_buffer
ret = call_bufop(vb->vb2_queue, fill_vb2_buffer,
vb, pb, vb->planes);
// 硬件相关的vb2_ops.buf_prepare, 对buffer做些准备工作
return ret ? ret : call_vb_qop(vb, buf_prepare, vb);
// 把buffer放入空闲链表
list_add_tail(&vb->queued_entry, &q->queued_list);
if (pb) // 调用vb2_buf_ops.copy_timestamp, 使用APP传入的v4l2_buffer来设置驱动的vb2_buffer
call_void_bufop(q, copy_timestamp, vb, pb);
/*
* If already streaming, give the buffer to driver for processing.
* If not, the buffer will be given to driver on next streamon.
*/
if (q->start_streaming_called)
__enqueue_in_driver(vb);
/* sync buffers */
for (plane = 0; plane < vb->num_planes; ++plane)
// 调用vb2_mem_ops.prepare做准备
call_void_memop(vb, prepare, vb->planes[plane].mem_priv);
// 调用硬件相关的vb2_ops.buf_queue把buffer传送给驱动
call_void_vb_qop(vb, buf_queue, vb);
/* Fill buffer information for the userspace */
if (pb) // 调用vb2_buf_ops.fill_user_buffer, 使用驱动的vb2_buffer为APP设置v4l2_buffer
call_void_bufop(q, fill_user_buffer, vb, pb);
/*
* If streamon has been called, and we haven't yet called
* start_streaming() since not enough buffers were queued, and
* we now have reached the minimum number of queued buffers,
* then we can finally call start_streaming().
*/
if (q->streaming && !q->start_streaming_called &&
q->queued_count >= q->min_buffers_needed) {
ret = vb2_start_streaming(q);
/*
* If any buffers were queued before streamon,
* we can now pass them to driver for processing.
*/
list_for_each_entry(vb, &q->queued_list, queued_entry)
__enqueue_in_driver(vb);
/* sync buffers */
for (plane = 0; plane < vb->num_planes; ++plane)
// 调用vb2_mem_ops.prepare做准备
call_void_memop(vb, prepare, vb->planes[plane].mem_priv);
// 调用硬件相关的vb2_ops.buf_queue把buffer传送给驱动
call_void_vb_qop(vb, buf_queue, vb);
/* Tell the driver to start streaming */
q->start_streaming_called = 1;
// 调用硬件相关的vb2_ops.start_streaming启动硬件传输
ret = call_qop(q, start_streaming, q,
atomic_read(&q->owned_by_drv_count));
```
情景分析3：把buffer取出队列
```shell
APP ioctl VIDIOC_DQBUF
------------------------------
v4l_dqbuf // v4l2-ioctl.c
ops->vidioc_dqbuf(file, fh, p);
vb2_ioctl_dqbuf // videobuf2-v4l2.c
vb2_dqbuf(vdev->queue, p, file->f_flags & O_NONBLOCK);
ret = vb2_core_dqbuf(q, NULL, b, nonblocking);
ret = __vb2_get_done_vb(q, &vb, pb, nonblocking);
ret = __vb2_wait_for_done_vb(q, nonblocking);
call_void_qop(q, wait_prepare, q);
wait_event_interruptible
call_void_qop(q, wait_finish, q);
*vb = list_first_entry(&q->done_list, struct vb2_buffer, done_entry);
if (pb)
ret = call_bufop(q, verify_planes_array, *vb, pb);
__verify_planes_array_core
__verify_planes_array(vb, pb);
if (!ret)
list_del(&(*vb)->done_entry);
call_void_vb_qop(vb, buf_finish, vb);
/* go back to dequeued state */
__vb2_dqbuf(vb);
call_void_memop(vb, unmap_dmabuf, vb->planes[i].mem_priv);
vb2_vmalloc_unmap_dmabuf
dma_buf_vunmap(buf->dbuf, buf->vaddr);
```
## 2. 从0编写一个虚拟的摄像头驱动

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@@ -231,10 +231,18 @@ V4L2 capture overlay
参考资料：
* https://www.linuxtv.org/downloads/v4l-dvb-apis-new/
* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/vidioc-create-bufs.html
* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/buffer.html#v4l2-memory
* 3种buffer：https://www.linuxtv.org/downloads/v4l-dvb-apis-old/index.html
* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/buffer.html#v4l2-memory
* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/mmap.html
* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/userp.html
* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/dmabuf.html
* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/vidioc-expbuf.html
* 基于Streaming I/O的V4L2设备使用： https://blog.csdn.net/coroutines/article/details/70141086
* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/mmap.html
* V4l2应用框架-Videobuf2数据结构 https://blog.csdn.net/weixin_42581177/article/details/126582465
* user ptr：https://github.com/h4tr3d/v4l2-capture-complex/blob/master/main.cpp
@@ -460,3 +468,19 @@ airspy_urb_complete
### 4.7 vidioc_prepare_buf
```c
v4l2_ioctl_ops.vidioc_prepare_buf
vb2_ioctl_prepare_buf
vb2_prepare_buf(vdev->queue, p);
vb2_core_prepare_buf(q, b->index, b)
call_void_bufop(q, fill_user_buffer, vb, pb);
__fill_v4l2_buffer
/**
* __fill_v4l2_buffer() - fill in a struct v4l2_buffer with information to be
* returned to userspace
*/
```