系列文章
高通msm-V4L2-Camera驱动浅析1-初识
高通msm-V4L2-Camera驱动浅析2-框架详解
高通msm-V4L2-Camera驱动浅析3-session
高通msm-V4L2-Camera驱动浅析4-stream
高通msm-V4L2-Camera驱动浅析5-buffer
一、stream(流)的设计思路
为什么要使用stream这个设计呢？
如果你做为开发者，现在你有个任务：假设camera像素为500W，你需要把每一帧500w的图像传输给用户使用，怎么办？
-
方法1：通过【帧IO】访问方式
使用read和write的方式，通过read读取每一帧数据，数据需要在内核和用户之间拷贝。但问题是：这种方式访问速度可能会非常慢。
一帧500W的数据量，一般场景下，我们的帧率都至少有20多帧，这种访问速度肯定不能接受。那怎么办呢？可不可以这样，我在内核申请一片内存(buf),然后把它映射(mmap)到用户空间，这样用户可以像直接读内存一样，访问到我们内核空间的数据。
-
方法2：通过【流IO】访问方式：
- 内存映射缓冲区(V4L2_MEMORY_MMAP)：在内核空间开辟缓冲区，应用通过mmap()系统调用映射到用户地址空间
- 用户空间缓冲区(V4L2_MEMORY_USERPTR)：在用户空间的应用中开辟缓冲区，用户与内核空间之间交换缓冲区指针。
因此stream(流)的概念就诞生了!
stream又涉及到图像的vb2_buffer，vb2_buffer又由vb2_queue 队列管理
关于vb2_buffer与vb2_queue在下一篇文章在进行讨论。
二、stream(流)的创建
2.1 stream(流)数据结构
struct msm_stream {
struct list_head list;//链表头
/* stream index per session, same
* as stream_id but set through s_parm
*/
unsigned int stream_id;//流id
/* vb2 buffer handling */
struct vb2_queue *vb2_q;//buf队列
spinlock_t stream_lock;
struct list_head queued_list;
};
2.2 session、stream、vb2_buffer的关系
上一篇文章里面有讲到，session中包含了stream的队列：
struct msm_session {
struct msm_queue_head stream_q;
}
stream里面又嵌入了struct vb2_queue *vb2_q队列;
而vb2_queue里面又包含用来保存和传输图像的buf——struct vb2_buffer *bufs[VB2_MAX_FRAME];
- session管理stream
- steam管理vb2_queue
- vb2_queue管理vb2_buffer
2.3 流的创建
int msm_create_stream(unsigned int session_id,
unsigned int stream_id, struct vb2_queue *q)
{
struct msm_session *session;
struct msm_stream *stream;
//根据session_id判断会话是否已经创建
session = msm_queue_find(msm_session_q, struct msm_session,
list, __msm_queue_find_session, &session_id);
if (!session)
return -EINVAL;
//申请内存
stream = kzalloc(sizeof(*stream), GFP_KERNEL);
if (!stream)
return -ENOMEM;
//赋值stream_id
stream->stream_id = stream_id;
//赋值vb2_queue队列
stream->vb2_q = q;
//初始化自旋锁
spin_lock_init(&stream->stream_lock);
//将新建立的流加入session管理的stream队列中
msm_enqueue(&session->stream_q, &stream->list);
//流的队列长度+1
session->stream_q.len++;
INIT_LIST_HEAD(&stream->queued_list);
return 0;
流包括很多，比如预览流，拍照流，元数据流等待，这些流都由统一的stream_q队列管理，每创建一个流，
就会入队。
2.4 流的创建流程-从hal到kernel
细致的调用流程，参考【Camera专题】HAL层-addChannel和startChannel简析
这里写一下关键的接口
用户空间：HAL层
hardware/qcom/camera/QCamera2/HAL/QCamera2HWI.cpp
int32_t QCamera2HardwareInterface::addPreviewChannel()
{
`
CDBG_HIGH("%s :zcf camera_handle=%d ops=%p", __func__,mCameraHandle->camera_handle,mCameraHandle->ops);
pChannel = new QCameraChannel(mCameraHandle->camera_handle,
mCameraHandle->ops);
···
// preview only channel, don't need bundle attr and cb
rc = pChannel->init(NULL, NULL, NULL);
···
// meta data stream always coexists with preview if applicable
rc = addStreamToChannel(pChannel, CAM_STREAM_TYPE_METADATA,
metadata_stream_cb_routine, this);
···
if (isNoDisplayMode()) {
rc = addStreamToChannel(pChannel, CAM_STREAM_TYPE_PREVIEW,
nodisplay_preview_stream_cb_routine, this);
} else {
rc = addStreamToChannel(pChannel, CAM_STREAM_TYPE_PREVIEW,
preview_stream_cb_routine, this);
}
···
if(···)
rc = addStreamToChannel(pChannel, CAM_STREAM_TYPE_ANALYSIS,
NULL, this);
m_channels[QCAMERA_CH_TYPE_PREVIEW] = pChannel;
return rc;
}
在启动预览的时候，添加了3路数据流，分别是：
- CAM_STREAM_TYPE_METADATA ： 元数据流
- CAM_STREAM_TYPE_PREVIEW：预览流
- CAM_STREAM_TYPE_ANALYSIS：人脸分析流
用户空间：HAL-mm-camera-interface
hardware/qcom/camera/QCamera2/stack/mm-camera-interface/src/mm_camera_stream.c
调用流程：
mm_channel_init
mm_camera_intf_add_channel
mm_camera_intf_add_stream
mm_channel_fsm_fn
mm_channel_fsm_fn_stopped
mm_channel_add_stream
mm_stream_fsm_fn/*获取流 */
mm_stream_fsm_inited
mm_stream_init
mm_stream_set_ext_mode
最终是调用到mm_stream_set_ext_mode
int32_t mm_stream_set_ext_mode(mm_stream_t * my_obj)
{
s_parm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
//通过IOCTL的方式，调用到内核。
rc = ioctl(my_obj->fd, VIDIOC_S_PARM, &s_parm);
return rc;
}
通过IOCTL的方式，调用到内核。
ioctl(my_obj->fd, VIDIOC_S_PARM, &s_parm);
内核空间
kernel/msm-4.9/drivers/media/v4l2-core/v4l2-ioctl.c
static struct v4l2_ioctl_info v4l2_ioctls[] = {
···
IOCTL_INFO_FNC(VIDIOC_S_PARM, v4l_s_parm, v4l_print_streamparm, INFO_FL_PRIO),
···
}
static int v4l_s_parm(const struct v4l2_ioctl_ops *ops,
struct file *file, void *fh, void *arg)
{
//调用vidioc_s_parm
return ops->vidioc_s_parm(file, fh, p);
}
kernel/msm-4.9/drivers/media/platform/msm/camera_v2/camera/camera.c
static const struct v4l2_ioctl_ops camera_v4l2_ioctl_ops = {
···
/* Stream type-dependent parameter ioctls */
.vidioc_g_parm = camera_v4l2_g_parm,
.vidioc_s_parm = camera_v4l2_s_parm,
···
};
在前面的文章，有说到ioctl_ops这个操作集合：
其中.vidioc_s_parm = camera_v4l2_s_parm。
static int camera_v4l2_s_parm(struct file *filep, void *fh,
struct v4l2_streamparm *parm)
{
//创建流
rc = msm_create_stream(event_data->session_id,
event_data->stream_id, &sp->vb2_q);
return rc;
}
三、log
HAL层关于数据流的定义：
typedef enum {
CAM_STREAM_TYPE_DEFAULT, /* default stream type */
CAM_STREAM_TYPE_PREVIEW, /* preview */
CAM_STREAM_TYPE_POSTVIEW, /* postview */
CAM_STREAM_TYPE_SNAPSHOT, /* snapshot */
CAM_STREAM_TYPE_VIDEO, /* video */
CAM_STREAM_TYPE_CALLBACK, /* app requested callback */
CAM_STREAM_TYPE_IMPL_DEFINED, /* opaque format: could be display, video enc, ZSL YUV */
CAM_STREAM_TYPE_METADATA, /* meta data */
CAM_STREAM_TYPE_RAW, /* raw dump from camif */
CAM_STREAM_TYPE_OFFLINE_PROC, /* offline process */
CAM_STREAM_TYPE_PARM, /* mct internal stream */
CAM_STREAM_TYPE_ANALYSIS, /* analysis stream */
CAM_STREAM_TYPE_DEPTH, /* Depth stream for depth sensor*/
CAM_STREAM_TYPE_MAX,
} cam_stream_type_t;
- CAM_STREAM_TYPE_PREVIEW = 1
- CAM_STREAM_TYPE_METADATA = 7
- CAM_STREAM_TYPE_ANALYSIS = 11
//hal 层
D QCamera : <MCI><DBG> mm_stream_fsm_inited: 596: open dev name =/dev/video1 , fd = 78
D QCamera : <MCI><DBG> mm_stream_set_ext_mode: 1894: E, my_handle = 0x900, fd = 78, state = 1
D QCamera : <MCI><DBG> mm_stream_set_ext_mode: 1901: stream fd=78, rc=0, extended_mode=1
//元数据流
D QCamera : <MCI><HIGH> mm_stream_calc_offset: 4876: Stream type 7 num_planes 1
D QCamera : <MCI><HIGH> mm_stream_calc_offset: 4883: Plane 0, stride 764376, scanline 1, width 764376, height 1,length 764416
//预览流
D QCamera : <MCI><HIGH> mm_stream_calc_offset: 4876: Stream type 1 num_planes 2
D QCamera : <MCI><HIGH> mm_stream_calc_offset: 4883: Plane 0, stride 384, scanline 320, width 360, height 320, length 122880
D QCamera : <MCI><HIGH> mm_stream_calc_offset: 4883: Plane 1, stride 384, scanline 160, width 360, height 160, length 61440
//人脸分析流
D QCamera : <MCI><HIGH> mm_stream_calc_offset: 4876: Stream type 11 num_planes 1
D QCamera : <MCI><HIGH> mm_stream_calc_offset: 4883: Plane 0, stride 544, scanline 480, width 540, height 480,length 261120
//kernel层
camera_v4l2_s_parm:session_id = 1,event_data->stream_id=1,sp->stream_id=1
camera_v4l2_s_parm:session_id = 1,event_data->stream_id=2,sp->stream_id=2
camera_v4l2_s_parm:session_id = 1,event_data->stream_id=3,sp->stream_id=3
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