imx6ull平台视频相关-ipu的EOF中断响应过程及用户空间map视频存储过程

一、imx6ull平台视频相关-ipu的EOF中断响应过程

ipu_csi_enc.c中的csi_enc_enabling_tasks注册EOF中断，EOF中断说如下：（在手册中摘阅）

该中断的回调函数实现也在ipu_csi_enc.c文件中-csi_enc_callback函数。

static irqreturn_t csi_enc_callback(int irq, void *dev_id)
{cam_data *cam = (cam_data *) dev_id;if (cam->enc_callback == NULL)return IRQ_HANDLED;cam->enc_callback(irq, dev_id);return IRQ_HANDLED;
}

cam->enc_callback(irq, dev_id);调用钩子函数，这个函数的注册在mxc_v4l2_capture.c的init_camera_struct函数中（贴出部分语句）。

 cam->enc_callback = camera_callback;init_waitqueue_head(&cam->power_queue);spin_lock_init(&cam->queue_int_lock);spin_lock_init(&cam->dqueue_int_lock);

camera_callback函数就是钩子的实体，也在mxc_v4l2_capture.c中。

static void camera_callback(u32 mask, void *dev)
{struct mxc_v4l_frame *done_frame;struct mxc_v4l_frame *ready_frame;struct timeval cur_time;cam_data *cam = (cam_data *) dev;if (cam == NULL)return;pr_debug("In MVC:camera_callback\n");spin_lock(&cam->queue_int_lock);spin_lock(&cam->dqueue_int_lock);if (!list_empty(&cam->working_q)) {do_gettimeofday(&cur_time);done_frame = list_entry(cam->working_q.next,struct mxc_v4l_frame,queue);if (done_frame->ipu_buf_num != cam->local_buf_num)goto next;/** Set the current time to done frame buffer's* timestamp. Users can use this information to judge* the frame's usage.*/done_frame->buffer.timestamp = cur_time;if (done_frame->buffer.flags & V4L2_BUF_FLAG_QUEUED) {done_frame->buffer.flags |= V4L2_BUF_FLAG_DONE;done_frame->buffer.flags &= ~V4L2_BUF_FLAG_QUEUED;/* Added to the done queue */list_del(cam->working_q.next);list_add_tail(&done_frame->queue, &cam->done_q);/* Wake up the queue */cam->enc_counter++;wake_up_interruptible(&cam->enc_queue);} elsepr_err("ERROR: v4l2 capture: camera_callback: ""buffer not queued\n");}next:if (!list_empty(&cam->ready_q)) {ready_frame = list_entry(cam->ready_q.next,struct mxc_v4l_frame,queue);if (cam->enc_update_eba)if (cam->enc_update_eba(cam,ready_frame->buffer.m.offset) == 0) {list_del(cam->ready_q.next);list_add_tail(&ready_frame->queue,&cam->working_q);ready_frame->ipu_buf_num = cam->local_buf_num;}} else {if (cam->enc_update_eba)cam->enc_update_eba(cam, cam->dummy_frame.buffer.m.offset);}cam->local_buf_num = (cam->local_buf_num == 0) ? 1 : 0;spin_unlock(&cam->dqueue_int_lock);spin_unlock(&cam->queue_int_lock);return;
}

一种方式是唤醒wake_up_interruptible(&cam->enc_queue);一种方式更新数据cam->enc_update_eba（cam, buffer.m.offset）。第一种情况响应的位置在mxc_v4l_dqueue中wait_event_interruptible_timeout(cam->enc_queue,cam->enc_counter != 0,10 * HZ)。第二种情况是调用了钩子cam->enc_update_eba，这个钩子的注册在ipu_csi_enc.c中的csi_enc_select函数中。

cam->enc_update_eba = csi_enc_eba_update;

csi_enc_eba_update函数的实现：

static int csi_enc_eba_update(void *private, dma_addr_t eba)
{int err = 0;cam_data *cam = (cam_data *) private;struct ipu_soc *ipu = cam->ipu;int *buffer_num = &cam->ping_pong_csi;ipu_channel_t chan = (cam->csi == 0) ? CSI_MEM0 : CSI_MEM1;pr_debug("eba %x\n", eba);err = ipu_update_channel_buffer(ipu, chan, IPU_OUTPUT_BUFFER,*buffer_num, eba);if (err != 0) {ipu_clear_buffer_ready(ipu, chan, IPU_OUTPUT_BUFFER,*buffer_num);err = ipu_update_channel_buffer(ipu, chan,IPU_OUTPUT_BUFFER, *buffer_num, eba);if (err != 0) {pr_err("ERROR: v4l2 capture: fail to update ""buf%d\n", *buffer_num);return err;}}ipu_select_buffer(ipu, chan, IPU_OUTPUT_BUFFER, *buffer_num);*buffer_num = (*buffer_num == 0) ? 1 : 0;return 0;
}

从ipu的通道中将数据搬到eba中，eba是上一步中的buffer.m.offset。而buffer.m.offset地址实际是被用户空间进行了map。

二、用户空间map视频存储过程

map的过程我分为了三步，第一步提出申请，第二步获取到内核层申请的内存空间并做映射，第三步获取视频数据。

我使用的上层应用代码是ffmpeg源码，其他源码也会进行相应的操作。

第一步：

在v4l2.c的mmap_init函数中，调用了v4l2_ioctl(s->fd, VIDIOC_REQBUFS, &req)。
VIDIOC_REQBUFS的实现在mxc_v4l2_capture.c。（为什么调用v4l2_ioctl会到case VIDIOC_REQBUFS, 如果不懂，请参考字符设备的ioctl函数的相关知识与实现）

 case VIDIOC_REQBUFS: {struct v4l2_requestbuffers *req = arg;pr_debug("   case VIDIOC_REQBUFS\n");if (req->count > FRAME_NUM) {pr_err("ERROR: v4l2 capture: VIDIOC_REQBUFS: ""not enough buffers\n");req->count = FRAME_NUM;}if ((req->type != V4L2_BUF_TYPE_VIDEO_CAPTURE)) {pr_err("ERROR: v4l2 capture: VIDIOC_REQBUFS: ""wrong buffer type\n");retval = -EINVAL;break;}mxc_streamoff(cam);if (req->memory & V4L2_MEMORY_MMAP) {mxc_free_frame_buf(cam);retval = mxc_allocate_frame_buf(cam, req->count);}break;}

这里在最后会判断是不是map（除了map还有read的方式等），如果是进入到mxc_allocate_frame_buf函数。

static int mxc_allocate_frame_buf(cam_data *cam, int count)
{int i;pr_debug("In MVC:mxc_allocate_frame_buf - size=%d\n",cam->v2f.fmt.pix.sizeimage);for (i = 0; i < count; i++) {cam->frame[i].vaddress =dma_alloc_coherent(0,PAGE_ALIGN(cam->v2f.fmt.pix.sizeimage),&cam->frame[i].paddress,GFP_DMA | GFP_KERNEL);if (cam->frame[i].vaddress == 0) {pr_err("ERROR: v4l2 capture: ""mxc_allocate_frame_buf failed.\n");mxc_free_frame_buf(cam);return -ENOBUFS;}cam->frame[i].buffer.index = i;cam->frame[i].buffer.flags = V4L2_BUF_FLAG_MAPPED;cam->frame[i].buffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;cam->frame[i].buffer.length =PAGE_ALIGN(cam->v2f.fmt.pix.sizeimage);cam->frame[i].buffer.memory = V4L2_MEMORY_MMAP;cam->frame[i].buffer.m.offset = cam->frame[i].paddress;cam->frame[i].index = i;}return 0;
}

mxc_allocate_frame_buf函数中调用了dma_alloc_coherent函数，我认为这个的作用是从dma的内存中申请一块固定大小的内存，返回虚拟地址，物理地址存在cam->frame[i].paddress里，并且这句话cam->frame[i].buffer.m.offset = cam->frame[i].paddress;，将cam->frame[i].paddress存在了cam->frame[i].buffer.m.offset中（buffer.m.offset就是函数csi_enc_eba_update最后搬移数据的目的地址）。

第二步：

还是在v4l2.c的mmap_init函数中，继续往下，调用了v4l2_ioctl(s->fd, VIDIOC_QUERYBUF, &buf)，
VIDIOC_QUERYBUF的实现在mxc_v4l2_capture.c。

 case VIDIOC_QUERYBUF: {struct v4l2_buffer *buf = arg;int index = buf->index;pr_debug("   case VIDIOC_QUERYBUF\n");if (buf->type != V4L2_BUF_TYPE_VIDEO_CAPTURE) {pr_err("ERROR: v4l2 capture: ""VIDIOC_QUERYBUFS: ""wrong buffer type\n");retval = -EINVAL;break;}if (buf->memory & V4L2_MEMORY_MMAP) {memset(buf, 0, sizeof(buf));buf->index = index;}down(&cam->param_lock);if (buf->memory & V4L2_MEMORY_USERPTR) {mxc_v4l2_release_bufs(cam);retval = mxc_v4l2_prepare_bufs(cam, buf);}if (buf->memory & V4L2_MEMORY_MMAP)retval = mxc_v4l2_buffer_status(cam, buf);up(&cam->param_lock);break;}

调用了mxc_v4l2_buffer_status函数。


```c
static int mxc_v4l2_buffer_status(cam_data *cam, struct v4l2_buffer *buf)
{pr_debug("In MVC:mxc_v4l2_buffer_status\n");if (buf->index < 0 || buf->index >= FRAME_NUM) {pr_err("ERROR: v4l2 capture: mxc_v4l2_buffer_status buffers ""not allocated\n");return -EINVAL;}memcpy(buf, &(cam->frame[buf->index].buffer), sizeof(*buf));return 0;
}

这个函数主要是做了信息的copy返回给用户空间（memcpy(buf, &(cam->frame[buf->index].buffer), sizeof(*buf));）。回到v4l2.c的mmap_init函数中，继续往下，```cs->buf_start[i] = v4l2_mmap(NULL, buf.length,PROT_READ | PROT_WRITE, MAP_SHARED,s->fd, buf.m.offset);

这句话做了遍映射，使用的物理地址就是上边提到的从dma中申请出来的buf.m.offset。

第三步：

第三步是读数据，在v4l2.c的mmap_read_frame中调用了v4l2_ioctl(s->fd, VIDIOC_DQBUF, &buf)，
VIDIOC_DQBUF的实现在mxc_v4l2_capture.c。

 case VIDIOC_DQBUF: {struct v4l2_buffer *buf = arg;pr_debug("   case VIDIOC_DQBUF\n");if ((cam->enc_counter == 0) &&(file->f_flags & O_NONBLOCK)) {retval = -EAGAIN;break;}retval = mxc_v4l_dqueue(cam, buf);break;}

进入mxc_v4l_dqueue函数：

static int mxc_v4l_dqueue(cam_data *cam, struct v4l2_buffer *buf)
{int retval = 0;struct mxc_v4l_frame *frame;unsigned long lock_flags;pr_debug("In MVC:mxc_v4l_dqueue\n");if (!wait_event_interruptible_timeout(cam->enc_queue,cam->enc_counter != 0,10 * HZ)) {pr_err("ERROR: v4l2 capture: mxc_v4l_dqueue timeout ""enc_counter %x\n",cam->enc_counter);return -ETIME;} else if (signal_pending(current)) {pr_err("ERROR: v4l2 capture: mxc_v4l_dqueue() ""interrupt received\n");return -ERESTARTSYS;}if (down_interruptible(&cam->busy_lock))return -EBUSY;spin_lock_irqsave(&cam->dqueue_int_lock, lock_flags);cam->enc_counter--;frame = list_entry(cam->done_q.next, struct mxc_v4l_frame, queue);list_del(cam->done_q.next);if (frame->buffer.flags & V4L2_BUF_FLAG_DONE) {frame->buffer.flags &= ~V4L2_BUF_FLAG_DONE;} else if (frame->buffer.flags & V4L2_BUF_FLAG_QUEUED) {pr_err("ERROR: v4l2 capture: VIDIOC_DQBUF: ""Buffer not filled.\n");frame->buffer.flags &= ~V4L2_BUF_FLAG_QUEUED;retval = -EINVAL;} else if ((frame->buffer.flags & 0x7) == V4L2_BUF_FLAG_MAPPED) {pr_err("ERROR: v4l2 capture: VIDIOC_DQBUF: ""Buffer not queued.\n");retval = -EINVAL;}cam->frame[frame->index].buffer.field = cam->device_type ?V4L2_FIELD_INTERLACED : V4L2_FIELD_NONE;buf->bytesused = cam->v2f.fmt.pix.sizeimage;buf->index = frame->index;buf->flags = frame->buffer.flags;buf->m = cam->frame[frame->index].buffer.m;buf->timestamp = cam->frame[frame->index].buffer.timestamp;buf->field = cam->frame[frame->index].buffer.field;spin_unlock_irqrestore(&cam->dqueue_int_lock, lock_flags);up(&cam->busy_lock);return retval;
}

可以看到上面提到的中断唤醒在此时就发挥作用了，如果不唤醒，则不会获取到数据。唤醒之后下面会从done_q队列中获取信息并返回给用户空间（队列还没太看懂，一共有三个队列done_q、ready_q、working_q）。

再回到v4l2.c的mmap_read_frame中。此时数据就在s->buf_start[buf.index]中，s->buf_start[buf.index]就是上面提到的映射的内存，根据获取到的信息，就可以读取出视频数据了。

个人分析，如果有错误，还望指正。