Linux v4l2驱动中vb2_buffer_done实现

概述

vb2_buffer_done 是驱动与videobuf2 交互的关键接口，驱动将一帧图像放入vb2 buffer时，再利用vb2_buffer_done将vb2 buffer送入videobuf2中；此函数的调用可以在中断中执行，也可以在进程中调用。

参数说明

/**
 * vb：vb2 buffer，此时驱动将一帧图像已经放入vb2 buffer
 * state：vb2 buffer状态，state为VB2_BUF_STATE_DONE时，通知 videobuf2取走buffer，state为VB2_BUF_STATE_ERROR时 通知videobuf2 buffer出错
 */
void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state);

函数原型

void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
{
	struct vb2_queue *q = vb->vb2_queue;
	unsigned long flags;

	if (WARN_ON(vb->state != VB2_BUF_STATE_ACTIVE))
		return;

	if (WARN_ON(state != VB2_BUF_STATE_DONE &&
		    state != VB2_BUF_STATE_ERROR &&
		    state != VB2_BUF_STATE_QUEUED))
		state = VB2_BUF_STATE_ERROR;           //check vb2 buffer状态

#ifdef CONFIG_VIDEO_ADV_DEBUG
	/*
	 * Although this is not a callback, it still does have to balance
	 * with the buf_queue op. So update this counter manually.
	 */
	vb->cnt_buf_done++;
#endif
	dprintk(q, 4, "done processing on buffer %d, state: %s\n",
		vb->index, vb2_state_name(state));

	if (state != VB2_BUF_STATE_QUEUED)
		__vb2_buf_mem_finish(vb);      //finish on buffer's private memory to sync caches，这里调用了vb2_queue->mem_ops->finish,最终执行函数为 vb2_cma_sg_finish(取决于vb2_queue->mem_ops的初始化)

	spin_lock_irqsave(&q->done_lock, flags);       //获取自旋锁，保存中断标志
	if (state == VB2_BUF_STATE_QUEUED) {
		vb->state = VB2_BUF_STATE_QUEUED;
	} else {
		/* Add the buffer to the done buffers list */
		list_add_tail(&vb->done_entry, &q->done_list);      //new entry to be added done_list
		vb->state = state;
	}
	atomic_dec(&q->owned_by_drv_count);        //驱动缓冲区的数量减去1

	if (state != VB2_BUF_STATE_QUEUED && vb->req_obj.req) {
		media_request_object_unbind(&vb->req_obj);
		media_request_object_put(&vb->req_obj);
	}

	spin_unlock_irqrestore(&q->done_lock, flags);         //释放自旋锁，恢复中断标志
    trace_vb2_buf_done(q, vb);

	switch (state) {
	case VB2_BUF_STATE_QUEUED:
		return;
	default:
		/* Inform any processes that may be waiting for buffers */
		wake_up(&q->done_wq);     //唤醒等待该缓冲区的进程，如果video_device->fops->poll = vb2_fop_poll, vb2_fop_poll中会收到通知(poll_wait捕获状态)
		break;
	}
}

vb2_buffer_done 在v4l2驱动中至关重要，比如isp硬件出来的图像都需要通过vb2_buffer_done送入videobuf2.