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weidongshan
@@ -142,6 +142,211 @@ APP操作buffer的示意图如下：
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#### 1.3.2 三类操作结构体
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V4L2中使用vb2_queue来管理缓冲区，里面有3个操作结构体：
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这3个操作结构体的作用为：
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* `const struct vb2_ops *ops`：驱动相关的回调函数，通过下面几个宏来调用
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* `const struct vb2_mem_ops *mem_ops`：分配内存用的回调函数
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* `const struct vb2_buf_ops *buf_ops`：在用户空间、内核空间之间传递buffer信息
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#### 1.3.3 vb2_ops
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`struct vb2_ops`示例如下：
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原型如下：
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```c
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struct vb2_ops {
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int (*queue_setup)(struct vb2_queue *q,
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unsigned int *num_buffers, unsigned int *num_planes,
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unsigned int sizes[], struct device *alloc_devs[]);
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void (*wait_prepare)(struct vb2_queue *q);
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void (*wait_finish)(struct vb2_queue *q);
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int (*buf_init)(struct vb2_buffer *vb);
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int (*buf_prepare)(struct vb2_buffer *vb);
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void (*buf_finish)(struct vb2_buffer *vb);
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void (*buf_cleanup)(struct vb2_buffer *vb);
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int (*start_streaming)(struct vb2_queue *q, unsigned int count);
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void (*stop_streaming)(struct vb2_queue *q);
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void (*buf_queue)(struct vb2_buffer *vb);
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};
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```
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各成员的作用为：
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| vb2_ops结构体成员 | 作用 |
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| ----------------- | ------------------------------------------------------------ |
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| 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"。 |
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| wait_prepare | 释放驱动自己的互斥锁 |
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| wait_finish | 申请驱动自己的互斥锁 |
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| 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 |
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| 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。 |
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| 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。 |
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| 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。 |
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| start_streaming | 驱动相关的"启动streaming"函数 |
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| stop_streaming | 驱动相关的"停止streaming"函数 |
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| 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。 |
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#### 1.3.4 vb2_mem_ops
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`struct vb2_mem_ops`示例如下：
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原型如下：
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```c
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struct vb2_mem_ops {
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void *(*alloc)(struct device *dev, unsigned long attrs,
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unsigned long size,
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enum dma_data_direction dma_dir,
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gfp_t gfp_flags);
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void (*put)(void *buf_priv);
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struct dma_buf *(*get_dmabuf)(void *buf_priv, unsigned long flags);
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void *(*get_userptr)(struct device *dev, unsigned long vaddr,
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unsigned long size,
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enum dma_data_direction dma_dir);
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void (*put_userptr)(void *buf_priv);
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void (*prepare)(void *buf_priv);
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void (*finish)(void *buf_priv);
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void *(*attach_dmabuf)(struct device *dev,
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struct dma_buf *dbuf,
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unsigned long size,
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enum dma_data_direction dma_dir);
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void (*detach_dmabuf)(void *buf_priv);
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int (*map_dmabuf)(void *buf_priv);
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void (*unmap_dmabuf)(void *buf_priv);
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void *(*vaddr)(void *buf_priv);
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void *(*cookie)(void *buf_priv);
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unsigned int (*num_users)(void *buf_priv);
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int (*mmap)(void *buf_priv, struct vm_area_struct *vma);
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};
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```
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各成员的作用为：
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| vb2_mem_ops结构体成员 | 作用 |
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| --------------------- | ------------------------------------------------------------ |
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| alloc | 分配真正用于存储视频数据的buffer，可能还分配私有数据 |
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| put | 通知分配器：这块buffer不再使用了。通常会释放内存。 |
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| get_dmabuf | 申请驱动自己的互斥锁 |
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| 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。 |
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| put_userptr | 通知分配器：这块USERPTR缓冲区不再使用 |
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| 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。 |
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| 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） |
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| map_dmabuf | 把DMA Buf映射到内核空间 |
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| unmap_dmabuf | map_dmabuf的反操作 |
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| 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。 |
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| 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。 |
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| vaddr | 返回这块内存的内核空间地址 |
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| cookie | 没什么用 |
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| num_users | 返回这块内存的引用计数 |
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| mmap | 把这块内存，映射到用户空间 |
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#### 1.3.5 vb2_buf_ops
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`struct vb2_buf_ops`示例如下：
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原型如下：
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```c
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struct vb2_buf_ops {
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int (*verify_planes_array)(struct vb2_buffer *vb, const void *pb);
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void (*fill_user_buffer)(struct vb2_buffer *vb, void *pb);
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int (*fill_vb2_buffer)(struct vb2_buffer *vb, const void *pb,
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struct vb2_plane *planes);
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void (*copy_timestamp)(struct vb2_buffer *vb, const void *pb);
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};
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```
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各成员的作用为：
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| vb2_buf_ops结构体成员 | 作用 |
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| --------------------- | ------------------------------------------------------------ |
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| 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。 |
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| 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。 |
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| 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。 |
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| 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。 |
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```c
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APP ioctl VIDIOC_PREPARE_BUF
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------------------------------
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v4l2_ioctl_ops.vidioc_prepare_buf
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vb2_ioctl_prepare_buf
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vb2_prepare_buf(vdev->queue, p);
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vb2_core_prepare_buf(q, b->index, b);
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ret = __buf_prepare(vb, pb);
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ret = __qbuf_mmap(vb, pb);
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if (pb)
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ret = call_bufop(vb->vb2_queue, fill_vb2_buffer,
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vb, pb, vb->planes);
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__fill_vb2_buffer
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return ret ? ret : call_vb_qop(vb, buf_prepare, vb);
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/* Fill buffer information for the userspace */
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call_void_bufop(q, fill_user_buffer, vb, pb);
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__fill_v4l2_buffer
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vb2_core_dqbuf
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ret = __vb2_get_done_vb(q, &vb, pb, nonblocking);
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ret = __vb2_wait_for_done_vb(q, nonblocking);
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call_void_qop(q, wait_prepare, q);
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wait_event_interruptible
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call_void_qop(q, wait_finish, q);
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*vb = list_first_entry(&q->done_list, struct vb2_buffer, done_entry);
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if (pb)
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ret = call_bufop(q, verify_planes_array, *vb, pb);
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__verify_planes_array_core
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__verify_planes_array(vb, pb);
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if (!ret)
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list_del(&(*vb)->done_entry);
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call_void_vb_qop(vb, buf_finish, vb);
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/* go back to dequeued state */
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__vb2_dqbuf(vb);
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call_void_memop(vb, unmap_dmabuf, vb->planes[i].mem_priv);
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vb2_vmalloc_unmap_dmabuf
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dma_buf_vunmap(buf->dbuf, buf->vaddr);
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vb2_core_qbuf
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if (pb)
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call_void_bufop(q, copy_timestamp, vb, pb);
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__copy_timestamp
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vb->timestamp = timeval_to_ns(&b->timestamp);
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```
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## 2. 从0编写一个虚拟的摄像头驱动
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BIN
IMX6ULL/doc_pic/13_V4L2/pic/30_vb2_queue_ops.png
Normal file
BIN
IMX6ULL/doc_pic/13_V4L2/pic/30_vb2_queue_ops.png
Normal file
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After Width: | Height: | Size: 40 KiB |
BIN
IMX6ULL/doc_pic/13_V4L2/pic/31_vbs_ops_example.png
Normal file
BIN
IMX6ULL/doc_pic/13_V4L2/pic/31_vbs_ops_example.png
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After Width: | Height: | Size: 27 KiB |
BIN
IMX6ULL/doc_pic/13_V4L2/pic/32_call_vbs_ops.png
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BIN
IMX6ULL/doc_pic/13_V4L2/pic/32_call_vbs_ops.png
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After Width: | Height: | Size: 43 KiB |
BIN
IMX6ULL/doc_pic/13_V4L2/pic/33_vb2_mem_ops_example.png
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BIN
IMX6ULL/doc_pic/13_V4L2/pic/33_vb2_mem_ops_example.png
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After Width: | Height: | Size: 43 KiB |
BIN
IMX6ULL/doc_pic/13_V4L2/pic/34_vb2_buf_ops_example.png
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BIN
IMX6ULL/doc_pic/13_V4L2/pic/34_vb2_buf_ops_example.png
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After Width: | Height: | Size: 26 KiB |
@@ -231,10 +231,18 @@ V4L2 capture overlay
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参考资料：
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* https://www.linuxtv.org/downloads/v4l-dvb-apis-new/
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* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/vidioc-create-bufs.html
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* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/buffer.html#v4l2-memory
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* 3种buffer：https://www.linuxtv.org/downloads/v4l-dvb-apis-old/index.html
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* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/buffer.html#v4l2-memory
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* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/mmap.html
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* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/userp.html
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* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/dmabuf.html
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* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/vidioc-expbuf.html
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* 基于Streaming I/O的V4L2设备使用： https://blog.csdn.net/coroutines/article/details/70141086
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* https://www.linuxtv.org/downloads/v4l-dvb-apis-old/mmap.html
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* V4l2应用框架-Videobuf2数据结构 https://blog.csdn.net/weixin_42581177/article/details/126582465
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* user ptr：https://github.com/h4tr3d/v4l2-capture-complex/blob/master/main.cpp
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@@ -460,3 +468,19 @@ airspy_urb_complete
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### 4.7 vidioc_prepare_buf
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```c
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v4l2_ioctl_ops.vidioc_prepare_buf
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vb2_ioctl_prepare_buf
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vb2_prepare_buf(vdev->queue, p);
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vb2_core_prepare_buf(q, b->index, b)
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call_void_bufop(q, fill_user_buffer, vb, pb);
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__fill_v4l2_buffer
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/**
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* __fill_v4l2_buffer() - fill in a struct v4l2_buffer with information to be
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* returned to userspace
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*/
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```
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