我们知道在HAL的Vendor实现当中会动态去load一个名字为camera.$platform$.so的档案，然后去加载Android HAL当中定义的方法，这里以Camera HAL 2.0并且Qualcomm msm8960为例子看下，结合之前的一篇文章(http://guoh.org/lifelog/2013/07/glance-at-camera-hal-2-0/)。
(注：这篇文章已经草稿比较久了，但是一直没有发出来，因为手里的这版代码没有设备可以跑，另外也无法确定代码是否完全正确，至少发现了一些地方都是stub实现，文中可能存在一些错误，如发现不正确的地方欢迎指出，我也会尽量发现错误并修正！)
我们知道在camera2.h当中定义了很多方法，那么在msm8960 HAL就是在如下地方
/path/to/qcam-hal/QCamera/HAL2
这编译出来就是一个camera.$platform$.so，请看它的实现
首先是HAL2/wrapper/QualcommCamera.h|cpp
/**
* The functions need to be provided by the camera HAL.
*
* If getNumberOfCameras() returns N, the valid cameraId for getCameraInfo()
* and openCameraHardware() is 0 to N-1.
*/
static hw_module_methods_t camera_module_methods = {
open: camera_device_open,
};
static hw_module_t camera_common = {
tag: HARDWARE_MODULE_TAG,
module_api_version: CAMERA_MODULE_API_VERSION_2_0, // 这样Camera Service才会去初始化Camera2Client一系列
hal_api_version: HARDWARE_HAL_API_VERSION,
id: CAMERA_HARDWARE_MODULE_ID,
name: "Qcamera",
author:"Qcom",
methods: &camera_module_methods,
dso: NULL,
reserved: {0},
};
camera_module_t HAL_MODULE_INFO_SYM = { // 这个HMI，每个HAL模块都必须有的
common: camera_common,
get_number_of_cameras: get_number_of_cameras,
get_camera_info: get_camera_info,
};
camera2_device_ops_t camera_ops = { // 注意这些绑定的函数
set_request_queue_src_ops: android::set_request_queue_src_ops,
notify_request_queue_not_empty: android::notify_request_queue_not_empty,
set_frame_queue_dst_ops: android::set_frame_queue_dst_ops,
get_in_progress_count: android::get_in_progress_count,
flush_captures_in_progress: android::flush_captures_in_progress,
construct_default_request: android::construct_default_request,
allocate_stream: android::allocate_stream,
register_stream_buffers: android::register_stream_buffers,
release_stream: android::release_stream,
allocate_reprocess_stream: android::allocate_reprocess_stream,
allocate_reprocess_stream_from_stream: android::allocate_reprocess_stream_from_stream,
release_reprocess_stream: android::release_reprocess_stream,
trigger_action: android::trigger_action,
set_notify_callback: android::set_notify_callback,
get_metadata_vendor_tag_ops: android::get_metadata_vendor_tag_ops,
dump: android::dump,
};
typedef struct { // 注意这个是Qualcomm自己定义的一个wrap结构
camera2_device_t hw_dev; // 这里是标准的
QCameraHardwareInterface *hardware;
int camera_released;
int cameraId;
} camera_hardware_t;
/* HAL should return NULL if it fails to open camera hardware. */
extern "C" int camera_device_open(
const struct hw_module_t* module, const char* id,
struct hw_device_t** hw_device)
{
int rc = -1;
int mode = 0;
camera2_device_t *device = NULL;
if (module && id && hw_device) {
int cameraId = atoi(id);
if (!strcmp(module->name, camera_common.name)) {
camera_hardware_t *camHal =
(camera_hardware_t *) malloc(sizeof (camera_hardware_t));
if (!camHal) {
*hw_device = NULL;
ALOGE("%s: end in no mem", __func__);
return rc;
}
/* we have the camera_hardware obj malloced */
memset(camHal, 0, sizeof (camera_hardware_t));
camHal->hardware = new QCameraHardwareInterface(cameraId, mode);
if (camHal->hardware && camHal->hardware->isCameraReady()) {
camHal->cameraId = cameraId;
device = &camHal->hw_dev; // 这里camera2_device_t
device->common.close = close_camera_device; // 初始化camera2_device_t
device->common.version = CAMERA_DEVICE_API_VERSION_2_0;
device->ops = &camera_ops;
device->priv = (void *)camHal;
rc = 0;
} else {
if (camHal->hardware) {
delete camHal->hardware;
camHal->hardware = NULL;
}
free(camHal);
device = NULL;
}
}
}
/* pass actual hw_device ptr to framework. This amkes that we actally be use memberof() macro */
*hw_device = (hw_device_t*)&device->common; // 这就是kernel或者Android native framework常用的一招
return rc;
}
看看allocate stream
int allocate_stream(const struct camera2_device *device,
uint32_t width,
uint32_t height,
int format,
const camera2_stream_ops_t *stream_ops,
uint32_t *stream_id,
uint32_t *format_actual,
uint32_t *usage,
uint32_t *max_buffers)
{
QCameraHardwareInterface *hardware = util_get_Hal_obj(device);
hardware->allocate_stream(width, height, format, stream_ops,
stream_id, format_actual, usage, max_buffers);
return rc;
}
这里注意QCameraHardwareInterface在QCameraHWI.h|cpp当中
int QCameraHardwareInterface::allocate_stream(
uint32_t width,
uint32_t height, int format,
const camera2_stream_ops_t *stream_ops,
uint32_t *stream_id,
uint32_t *format_actual,
uint32_t *usage,
uint32_t *max_buffers)
{
int ret = OK;
QCameraStream *stream = NULL;
camera_mode_t myMode = (camera_mode_t)(CAMERA_MODE_2D|CAMERA_NONZSL_MODE);
stream = QCameraStream_preview::createInstance(
mCameraHandle->camera_handle,
mChannelId,
width,
height,
format,
mCameraHandle,
myMode);
stream->setPreviewWindow(stream_ops); // 这里，也就是只要通过该方法创建的stream，都会有对应的ANativeWindow进来
*stream_id = stream->getStreamId();
*max_buffers= stream->getMaxBuffers(); // 从HAL得到的
*usage = GRALLOC_USAGE_HW_CAMERA_WRITE | CAMERA_GRALLOC_HEAP_ID
| CAMERA_GRALLOC_FALLBACK_HEAP_ID;
/* Set to an arbitrary format SUPPORTED by gralloc */
*format_actual = HAL_PIXEL_FORMAT_YCrCb_420_SP;
return ret;
}
QCameraStream_preview::createInstance直接调用自己的构造方法，也就是下面
(相关class在QCameraStream.h|cpp和QCameraStream_Preview.cpp)
QCameraStream_preview::QCameraStream_preview(uint32_t CameraHandle,
uint32_t ChannelId,
uint32_t Width,
uint32_t Height,
int requestedFormat,
mm_camera_vtbl_t *mm_ops,
camera_mode_t mode) :
QCameraStream(CameraHandle,
ChannelId,
Width,
Height,
mm_ops,
mode),
mLastQueuedFrame(NULL),
mDisplayBuf(NULL),
mNumFDRcvd(0)
{
mStreamId = allocateStreamId(); // 分配stream id(根据mStreamTable)
switch (requestedFormat) { // max buffer number
case CAMERA2_HAL_PIXEL_FORMAT_OPAQUE:
mMaxBuffers = 5;
break;
case HAL_PIXEL_FORMAT_BLOB:
mMaxBuffers = 1;
break;
default:
ALOGE("Unsupported requested format %d", requestedFormat);
mMaxBuffers = 1;
break;
}
/*TODO: There has to be a better way to do this*/
}
再看看
/path/to/qcam-hal/QCamera/stack/mm-camera-interface/
mm_camera_interface.h
当中
typedef struct {
uint32_t camera_handle; /* camera object handle */
mm_camera_info_t *camera_info; /* reference pointer of camear info */
mm_camera_ops_t *ops; /* API call table */
} mm_camera_vtbl_t;
mm_camera_interface.c
当中
/* camera ops v-table */
static mm_camera_ops_t mm_camera_ops = {
.sync = mm_camera_intf_sync,
.is_event_supported = mm_camera_intf_is_event_supported,
.register_event_notify = mm_camera_intf_register_event_notify,
.qbuf = mm_camera_intf_qbuf,
.camera_close = mm_camera_intf_close,
.query_2nd_sensor_info = mm_camera_intf_query_2nd_sensor_info,
.is_parm_supported = mm_camera_intf_is_parm_supported,
.set_parm = mm_camera_intf_set_parm,
.get_parm = mm_camera_intf_get_parm,
.ch_acquire = mm_camera_intf_add_channel,
.ch_release = mm_camera_intf_del_channel,
.add_stream = mm_camera_intf_add_stream,
.del_stream = mm_camera_intf_del_stream,
.config_stream = mm_camera_intf_config_stream,
.init_stream_bundle = mm_camera_intf_bundle_streams,
.destroy_stream_bundle = mm_camera_intf_destroy_bundle,
.start_streams = mm_camera_intf_start_streams,
.stop_streams = mm_camera_intf_stop_streams,
.async_teardown_streams = mm_camera_intf_async_teardown_streams,
.request_super_buf = mm_camera_intf_request_super_buf,
.cancel_super_buf_request = mm_camera_intf_cancel_super_buf_request,
.start_focus = mm_camera_intf_start_focus,
.abort_focus = mm_camera_intf_abort_focus,
.prepare_snapshot = mm_camera_intf_prepare_snapshot,
.set_stream_parm = mm_camera_intf_set_stream_parm,
.get_stream_parm = mm_camera_intf_get_stream_parm
};
以start stream为例子
mm_camera_intf_start_streams(mm_camera_interface
mm_camera_start_streams(mm_camera
mm_channel_fsm_fn(mm_camera_channel
mm_channel_fsm_fn_active(mm_camera_channel
mm_channel_start_streams(mm_camera_channel
mm_stream_fsm_fn(mm_camera_stream
mm_stream_fsm_reg(mm_camera_stream
mm_camera_cmd_thread_launch(mm_camera_data
mm_stream_streamon(mm_camera_stream
注意：本文当中，如上这种梯度摆放，表示是调用关系，如果梯度是一样的，就表示这些方法是在上层同一个方法里面被调用的
int32_t mm_stream_streamon(mm_stream_t *my_obj)
{
int32_t rc;
enum v4l2_buf_type buf_type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE;
/* Add fd to data poll thread */
rc = mm_camera_poll_thread_add_poll_fd(&my_obj->ch_obj->poll_thread[0],
my_obj->my_hdl,
my_obj->fd,
mm_stream_data_notify,
(void*)my_obj);
if (rc < 0) {
return rc;
}
rc = ioctl(my_obj->fd, VIDIOC_STREAMON, &buf_type);
if (rc < 0) {
CDBG_ERROR("%s: ioctl VIDIOC_STREAMON failed: rc=%d\n",
__func__, rc);
/* remove fd from data poll thread in case of failure */
mm_camera_poll_thread_del_poll_fd(&my_obj->ch_obj->poll_thread[0], my_obj->my_hdl);
}
return rc;
}
看到ioctl，VIDIOC_STREAMON，可以高兴一下了，这就是V4L2规范当中用户空间和内核空间通信的方法，V4L2(Video for Linux Two)是一种经典而且成熟的视频通信协议，之前是V4L，不清楚的可以去下载它的规范，另外The Video4Linux2(http://lwn.net/Articles/203924/)也是很好的资料。
这里简单介绍下：
open(VIDEO_DEVICE_NAME, …) // 开启视频设备，一般在程序初始化的时候调用
ioctl(…) // 主要是一些需要传输数据量很小的控制操作
这里可以用的参数很多，并且通常来说我们会按照以下方式来使用，比如
VIDIOC_QUERYCAP // 查询设备能干什么
VIDIOC_CROPCAP // 查询设备crop能力
VIDIOC_S_* // set/get方法，设置/获取参数
VIDIOC_G_*
VIDIOC_REQBUFS // 分配buffer，可以有多种方式
VIDIOC_QUERYBUF // 查询分配的buffer的信息
VIDIOC_QBUF // QUEUE BUFFER 把buffer压入DRV缓存队列(这时候buffer是空的)
VIDIOC_STREAMON // 开始视频数据传输
VIDIOC_DQBUF // DEQUEUE BUFFER 把buffer从DRV缓存队列中取出(这时候buffer是有数据的)[0…n]
QBUF -> DQBUF // 可以一直重复这个动作VIDIOC_STREAMOFF // 停止视频数据传输
close(VIDEO_DEVICE_FD) // 关闭设备
上面就是主要的函数和简单的调用顺序，另外还有几个函数select() // 等待事件发生，主要用在我们把存frame的buffer推给DRV以后，等待它的反应
mmap/munmap // 主要处理我们request的buffer的，buffer分配在设备的内存空间的时候需要
并且看看mm_camera_stream这个文件里面也都是这么实现的。
看完这里，我们回过头来继续看QCam HAL，当然它实现的细节也不是我上面start stream所列的那么简单，但是其实也不算复杂，觉得重要的就是状态和用到的结构。
首先是channel状态，目前只支持1个channel，但是可以有多个streams(后面会介绍，而且目前最多支持8个streams)
/* mm_channel */
typedef enum {
MM_CHANNEL_STATE_NOTUSED = 0, /* not used */
MM_CHANNEL_STATE_STOPPED, /* stopped */
MM_CHANNEL_STATE_ACTIVE, /* active, at least one stream active */
MM_CHANNEL_STATE_PAUSED, /* paused */
MM_CHANNEL_STATE_MAX
} mm_channel_state_type_t;
它可以执行的事件
typedef enum {
MM_CHANNEL_EVT_ADD_STREAM,
MM_CHANNEL_EVT_DEL_STREAM,
MM_CHANNEL_EVT_START_STREAM,
MM_CHANNEL_EVT_STOP_STREAM,
MM_CHANNEL_EVT_TEARDOWN_STREAM,
MM_CHANNEL_EVT_CONFIG_STREAM,
MM_CHANNEL_EVT_PAUSE,
MM_CHANNEL_EVT_RESUME,
MM_CHANNEL_EVT_INIT_BUNDLE,
MM_CHANNEL_EVT_DESTROY_BUNDLE,
MM_CHANNEL_EVT_REQUEST_SUPER_BUF,
MM_CHANNEL_EVT_CANCEL_REQUEST_SUPER_BUF,
MM_CHANNEL_EVT_START_FOCUS,
MM_CHANNEL_EVT_ABORT_FOCUS,
MM_CHANNEL_EVT_PREPARE_SNAPSHOT,
MM_CHANNEL_EVT_SET_STREAM_PARM,
MM_CHANNEL_EVT_GET_STREAM_PARM,
MM_CHANNEL_EVT_DELETE,
MM_CHANNEL_EVT_MAX
} mm_channel_evt_type_t;
/* mm_stream */
typedef enum { // 这里的状态要仔细，每执行一次方法，状态就需要变化
MM_STREAM_STATE_NOTUSED = 0, /* not used */
MM_STREAM_STATE_INITED, /* inited */
MM_STREAM_STATE_ACQUIRED, /* acquired, fd opened */
MM_STREAM_STATE_CFG, /* fmt & dim configured */
MM_STREAM_STATE_BUFFED, /* buf allocated */
MM_STREAM_STATE_REG, /* buf regged, stream off */
MM_STREAM_STATE_ACTIVE_STREAM_ON, /* active with stream on */
MM_STREAM_STATE_ACTIVE_STREAM_OFF, /* active with stream off */
MM_STREAM_STATE_MAX
} mm_stream_state_type_t;
同样，stream可以执行的事件
typedef enum {
MM_STREAM_EVT_ACQUIRE,
MM_STREAM_EVT_RELEASE,
MM_STREAM_EVT_SET_FMT,
MM_STREAM_EVT_GET_BUF,
MM_STREAM_EVT_PUT_BUF,
MM_STREAM_EVT_REG_BUF,
MM_STREAM_EVT_UNREG_BUF,
MM_STREAM_EVT_START,
MM_STREAM_EVT_STOP,
MM_STREAM_EVT_QBUF,
MM_STREAM_EVT_SET_PARM,
MM_STREAM_EVT_GET_PARM,
MM_STREAM_EVT_MAX
} mm_stream_evt_type_t;
这里每次执行函数的时候都需要检查channel/stream的状态，只有状态正确的时候才会去执行
比如你可以观察到
mm_channel的mm_channel_state_type_t state;
mm_stream的mm_stream_state_type_t state;
均表示这个结构当前的状态
另外
struct mm_camera_obj
struct mm_channel
struct mm_stream
这三个也是自上而下包含的，并且stream和channel还会持有父结构(暂且这么称呼，实际为container关系)的引用。
实际上Vendor的HAL每个都有自己实现的方法，也可能包含很多特有的东西，比如这里它会喂给ioctl一些特有的命令或者数据结构，这些我们就只有在做特定平台的时候去考虑了。这些都可能千变万化，比如OMAP4它同DRV沟通是透过rpmsg，并用OpenMAX的一套规范来实现的。
理论就这么多，接着看一个实例，比如我们在Camera Service要去start preview：
Camera2Client::startPreviewL StreamingProcessor->updatePreviewStream Camera2Device->createStream StreamAdapter->connectToDevice camera2_device_t->ops->allocate_stream // 上面有分析 native_window_api_*或者native_window_* StreamingProcessor->startStream Camera2Device->setStreamingRequest Camera2Device::RequestQueue->setStreamSlot // 创建一个stream slot Camera2Device::RequestQueue->signalConsumerLocked
status_t Camera2Device::MetadataQueue::signalConsumerLocked() {
status_t res = OK;
notEmpty.signal();
if (mSignalConsumer && mDevice != NULL) {
mSignalConsumer = false;
mMutex.unlock();
res = mDevice->ops->notify_request_queue_not_empty(mDevice); // 通知Vendor HAL的run command thread去运行，
// notify_request_queue_not_empty这个事件不是每次都会触发的，只有初始化时候
// 或者run command thread在dequeue的时候发现数据为NULL，
// 而Camera Service之变又有新的request进来的时候才会去触发
// 可以说是减轻负担吧，不用没有请求的时候，thread也一直在那里
// 不过通常碰到这样的情况都是利用锁让thread停在那里
mMutex.lock();
}
return res;
}
然而在Qualcomm HAL当中
int notify_request_queue_not_empty(const struct camera2_device *device) // 这个方法注册到camera2_device_ops_t当中 QCameraHardwareInterface->notify_request_queue_not_empty() pthread_create(&mCommandThread, &attr, command_thread, (void *)this) != 0)
void *command_thread(void *obj)
{
...
pme->runCommandThread(obj);
}
void QCameraHardwareInterface::runCommandThread(void *data)
{
/**
* This function implements the main service routine for the incoming
* frame requests, this thread routine is started everytime we get a
* notify_request_queue_not_empty trigger, this thread makes the
* assumption that once it receives a NULL on a dequest_request call
* there will be a fresh notify_request_queue_not_empty call that is
* invoked thereby launching a new instance of this thread. Therefore,
* once we get a NULL on a dequeue request we simply let this thread die
*/
int res;
camera_metadata_t *request=NULL;
mPendingRequests=0;
while (mRequestQueueSrc) { // mRequestQueueSrc是通过set_request_queue_src_ops设置进来的
// 参见Camera2Device::MetadataQueue::setConsumerDevice
// 在Camera2Device::initialize当中被调用
ALOGV("%s:Dequeue request using mRequestQueueSrc:%p",__func__,mRequestQueueSrc);
mRequestQueueSrc->dequeue_request(mRequestQueueSrc, &request); // 取framework request
if (request==NULL) {
ALOGE("%s:No more requests available from src command \
thread dying",__func__);
return;
}
mPendingRequests++;
/* Set the metadata values */
/* Wait for the SOF for the new metadata values to be applied */
/* Check the streams that need to be active in the stream request */
sort_camera_metadata(request);
camera_metadata_entry_t streams;
res = find_camera_metadata_entry(request,
ANDROID_REQUEST_OUTPUT_STREAMS,
&streams);
if (res != NO_ERROR) {
ALOGE("%s: error reading output stream tag", __FUNCTION__);
return;
}
res = tryRestartStreams(streams); // 会去prepareStream和streamOn，后面有详细代码
if (res != NO_ERROR) {
ALOGE("error tryRestartStreams %d", res);
return;
}
/* 3rd pass: Turn on all streams requested */
for (uint32_t i = 0; i < streams.count; i++) {
int streamId = streams.data.u8[i];
QCameraStream *stream = QCameraStream::getStreamAtId(streamId);
/* Increment the frame pending count in each stream class */
/* Assuming we will have the stream obj in had at this point may be
* may be multiple objs in which case we loop through array of streams */
stream->onNewRequest();
}
ALOGV("%s:Freeing request using mRequestQueueSrc:%p",__func__,mRequestQueueSrc);
/* Free the request buffer */
mRequestQueueSrc->free_request(mRequestQueueSrc,request);
mPendingRequests--;
ALOGV("%s:Completed request",__func__);
}
QCameraStream::streamOffAll();
}
下面这个方法解释mRequestQueueSrc来自何处
// Connect to camera2 HAL as consumer (input requests/reprocessing)
status_t Camera2Device::MetadataQueue::setConsumerDevice(camera2_device_t *d) {
ATRACE_CALL();
status_t res;
res = d->ops->set_request_queue_src_ops(d,
this);
if (res != OK) return res;
mDevice = d;
return OK;
}
因为
QCameraStream_preview->prepareStream QCameraStream->initStream mm_camera_vtbl_t->ops->add_stream(... stream_cb_routine ...) // 这是用来返回数据的callback，带mm_camera_super_buf_t*和void*两参数 mm_camera_add_stream mm_channel_fsm_fn(..., MM_CHANNEL_EVT_ADD_STREAM, ..., mm_evt_paylod_add_stream_t) mm_channel_fsm_fn_stopped mm_channel_add_stream(..., mm_camera_buf_notify_t, ...) mm_stream_fsm_inited
而
在mm_channel_add_stream当中有把mm_camera_buf_notify_t包装到mm_stream_t
mm_stream_t *stream_obj = NULL; /* initialize stream object */ memset(stream_obj, 0, sizeof(mm_stream_t)); /* cd through intf always palced at idx 0 of buf_cb */ stream_obj->buf_cb[0].cb = buf_cb; // callback stream_obj->buf_cb[0].user_data = user_data; stream_obj->buf_cb[0].cb_count = -1; /* infinite by default */ // 默认无限次数
并且mm_stream_fsm_inited，传进来的event参数也是MM_STREAM_EVT_ACQUIRE
int32_t mm_stream_fsm_inited(mm_stream_t *my_obj,
mm_stream_evt_type_t evt,
void * in_val,
void * out_val)
{
int32_t rc = 0;
char dev_name[MM_CAMERA_DEV_NAME_LEN];
switch (evt) {
case MM_STREAM_EVT_ACQUIRE:
if ((NULL == my_obj->ch_obj) || (NULL == my_obj->ch_obj->cam_obj)) {
CDBG_ERROR("%s: NULL channel or camera obj\n", __func__);
rc = -1;
break;
}
snprintf(dev_name, sizeof(dev_name), "/dev/%s",
mm_camera_util_get_dev_name(my_obj->ch_obj->cam_obj->my_hdl));
my_obj->fd = open(dev_name, O_RDWR | O_NONBLOCK); // 打开视频设备
if (my_obj->fd <= 0) {
CDBG_ERROR("%s: open dev returned %d\n", __func__, my_obj->fd);
rc = -1;
break;
}
rc = mm_stream_set_ext_mode(my_obj);
if (0 == rc) {
my_obj->state = MM_STREAM_STATE_ACQUIRED; // mm_stream_state_type_t
} else {
/* failed setting ext_mode
* close fd */
if(my_obj->fd > 0) {
close(my_obj->fd);
my_obj->fd = -1;
}
break;
}
rc = get_stream_inst_handle(my_obj);
if(rc) {
if(my_obj->fd > 0) {
close(my_obj->fd);
my_obj->fd = -1;
}
}
break;
default:
CDBG_ERROR("%s: Invalid evt=%d, stream_state=%d",
__func__,evt,my_obj->state);
rc = -1;
break;
}
return rc;
}
还有
QCameraStream->streamOn mm_camera_vtbl_t->ops->start_streams mm_camera_intf_start_streams mm_camera_start_streams mm_channel_fsm_fn(..., MM_CHANNEL_EVT_START_STREAM, ...) mm_stream_fsm_fn(..., MM_STREAM_EVT_START, ...) mm_camera_cmd_thread_launch // 启动CB线程 mm_stream_streamon(mm_stream_t) mm_camera_poll_thread_add_poll_fd(..., mm_stream_data_notify , ...)
而
static void mm_stream_data_notify(void* user_data)
{
mm_stream_t *my_obj = (mm_stream_t*)user_data;
int32_t idx = -1, i, rc;
uint8_t has_cb = 0;
mm_camera_buf_info_t buf_info;
if (NULL == my_obj) {
return;
}
if (MM_STREAM_STATE_ACTIVE_STREAM_ON != my_obj->state) {
/* this Cb will only received in active_stream_on state
* if not so, return here */
CDBG_ERROR("%s: ERROR!! Wrong state (%d) to receive data notify!",
__func__, my_obj->state);
return;
}
memset(&buf_info, 0, sizeof(mm_camera_buf_info_t));
pthread_mutex_lock(&my_obj->buf_lock);
rc = mm_stream_read_msm_frame(my_obj, &buf_info); // 通过ioctl(..., VIDIOC_DQBUF, ...)读取frame数据
if (rc != 0) {
pthread_mutex_unlock(&my_obj->buf_lock);
return;
}
idx = buf_info.buf->buf_idx;
/* update buffer location */
my_obj->buf_status[idx].in_kernel = 0;
/* update buf ref count */
if (my_obj->is_bundled) {
/* need to add into super buf since bundled, add ref count */
my_obj->buf_status[idx].buf_refcnt++;
}
for (i=0; i < MM_CAMERA_STREAM_BUF_CB_MAX; i++) {
if(NULL != my_obj->buf_cb[i].cb) {
/* for every CB, add ref count */
my_obj->buf_status[idx].buf_refcnt++;
has_cb = 1;
}
}
pthread_mutex_unlock(&my_obj->buf_lock);
mm_stream_handle_rcvd_buf(my_obj, &buf_info); // mm_camera_queue_enq，往queue里面丢frame数据(
// 前提是有注册callback)，并透过sem_post通知queue
// 然后mm_camera_cmd_thread_launch启动的线程会
// 轮循读取数据，然后执行CB
}
这样就会导致在stream on的时候stream_cb_routine(实现在QCameraStream当中)就会一直执行
void stream_cb_routine(mm_camera_super_buf_t *bufs,
void *userdata)
{
QCameraStream *p_obj=(QCameraStream*) userdata;
switch (p_obj->mExtImgMode) { // 这个mode在prepareStream的时候就会确定
case MM_CAMERA_PREVIEW:
ALOGE("%s : callback for MM_CAMERA_PREVIEW", __func__);
((QCameraStream_preview *)p_obj)->dataCallback(bufs); // CAMERA_PREVIEW和CAMERA_VIDEO是一样的？
break;
case MM_CAMERA_VIDEO:
ALOGE("%s : callback for MM_CAMERA_VIDEO", __func__);
((QCameraStream_preview *)p_obj)->dataCallback(bufs);
break;
case MM_CAMERA_SNAPSHOT_MAIN:
ALOGE("%s : callback for MM_CAMERA_SNAPSHOT_MAIN", __func__);
p_obj->p_mm_ops->ops->qbuf(p_obj->mCameraHandle,
p_obj->mChannelId,
bufs->bufs[0]);
break;
case MM_CAMERA_SNAPSHOT_THUMBNAIL:
break;
default:
break;
}
}
void QCameraStream::dataCallback(mm_camera_super_buf_t *bufs)
{
if (mPendingCount != 0) { // 这个dataCallback是一直在都在回来么？
// 而且从代码来看设置下去的callback次数默认是-1，-1就表示infinite。
// 似乎只能这样才能解释，否则没人触发的话，即使mPendingCount在onNewRequest当中加1了
// 这里也感知不到
ALOGD("Got frame request");
pthread_mutex_lock(&mFrameDeliveredMutex);
mPendingCount--;
ALOGD("Completed frame request");
pthread_cond_signal(&mFrameDeliveredCond);
pthread_mutex_unlock(&mFrameDeliveredMutex);
processPreviewFrame(bufs);
} else {
p_mm_ops->ops->qbuf(mCameraHandle,
mChannelId, bufs->bufs[0]); // 如果没有需要数据的情况，直接把buffer压入DRV的队列当中，会call到V4L2的QBUF
}
}
比较好奇的是在手里这版QCam HAL的code当中camera2_frame_queue_dst_ops_t没有被用到
int QCameraHardwareInterface::set_frame_queue_dst_ops(
const camera2_frame_queue_dst_ops_t *frame_dst_ops)
{
mFrameQueueDst = frame_dst_ops; // 这个现在似乎没有用到嘛
return OK;
}
这样Camera Service的FrameProcessor的Camera2Device->getNextFrame就永远也获取不到数据，不知道是不是我手里的这版代码的问题，而且在最新的Qualcomm Camera HAL代码也不在AOSP树当中了，而是直接以proprietary形式给的so档，这只是题外话。
所以总体来看，这里可能有几个QCameraStream，每个stream负责自己的事情。
他们之间也有相互关系，比如有可能新的stream进来会导致其他已经stream-on的stream重新启动。
在Camera HAL 2.0当中我们还有个重点就是re-process stream
简单的说就是把output stream作为input stream再次添加到BufferQueue中，让其他的consumer来处理，就类似一个chain一样。
目前在ZslProcessor当中有用到。
ZslProcessor->updateStream Camera2Device->createStream Camera2Device->createReprocessStreamFromStream // release的时候是先delete re-process new ReprocessStreamAdapter ReprocessStreamAdapter->connectToDevice camera2_device_t->ops->allocate_reprocess_stream_from_stream
这里ReprocessStreamAdapter实际就是camera2_stream_in_ops_t，负责管理re-process的stream。
但是这版的代码Qualcomm也似乎没有去实现，所以暂时到此为止，如果后面找到相应的代码，再来看。
所以看完这么多不必觉得惊讶，站在Camera Service的立场，它持有两个MetadataQueue，mRequestQueue和mFrameQueue。
app请求的动作，比如set parameter/start preview/start recording会直接转化为request，放到mRequestQueue，然后去重启preview/recording stream。
比如capture也会转换为request，放到mRequestQueue。
如果有必要，会通过notify_request_queue_not_empty去通知QCam HAL有请求需要处理，然后QCam HAL会启动一个线程(QCameraHardwareInterface::runCommandThread)去做处理。直到所有request处理完毕退出线程。
在这个处理的过程当中会分别调用到每个stream的processPreviewFrame，有必要的话它每个都会调用自己后续的callback。
还有一个实现的细节就是，stream_cb_routine是从start stream就有开始注册在同一个channel上的，而stream_cb_routine间接调用QCameraStream::dataCallback(当然stream_cb_routine有去指定这个callback回来的原因是什么，就好调用对应的dataCallback)，这个callback是一直都在回来，所以每次new request让mPendingCount加1之后，dataCallback回来才会调用processPreviewFrame，否则就直接把buffer再次压回DRV队列当中。
void QCameraStream::dataCallback(mm_camera_super_buf_t *bufs)
{
if (mPendingCount != 0) { // 这个dataCallback是一直在都在回来么？
// 而且从代码来看设置下去的callback次数默认是-1，-1就表示infinite。
// 似乎只能这样才能解释，否则没人触发的话，即使mPendingCount在onNewRequest当中加1了
// 这里也感知不到
ALOGD("Got frame request");
pthread_mutex_lock(&mFrameDeliveredMutex);
mPendingCount--;
ALOGD("Completed frame request");
pthread_cond_signal(&mFrameDeliveredCond);
pthread_mutex_unlock(&mFrameDeliveredMutex);
processPreviewFrame(bufs);
} else {
p_mm_ops->ops->qbuf(mCameraHandle,
mChannelId, bufs->bufs[0]); // 如果没有需要数据的情况，直接把buffer压入DRV的队列当中，会call到V4L2的QBUF
}
}
void QCameraStream::onNewRequest()
{
ALOGI("%s:E",__func__);
pthread_mutex_lock(&mFrameDeliveredMutex);
ALOGI("Sending Frame request");
mPendingCount++;
pthread_cond_wait(&mFrameDeliveredCond, &mFrameDeliveredMutex); // 等带一个请求处理完，再做下一个请求
ALOGV("Got frame");
pthread_mutex_unlock(&mFrameDeliveredMutex);
ALOGV("%s:X",__func__);
}
processPreviewFrame会调用到创建这个stream的时候关联进来的那个BufferQueue的enqueue_buffer方法，把数据塞到BufferQueue中，然后对应的consumer就会收到了。
比如在Android Camera HAL 2.0当中目前有
camera2/BurstCapture.h
camera2/CallbackProcessor.h
camera2/JpegProcessor.h
camera2/StreamingProcessor.h
camera2/ZslProcessor.h
实现了对应的Consumer::FrameAvailableListener，但是burst-capture现在可以不考虑，因为都还只是stub实现。
ZslProcessor.h和CaptureSequencer.h都有去实现FrameProcessor::FilteredListener的onFrameAvailable(…)
但是我们之前讲过这版QCam HAL没有实现，所以FrameProcessor是无法获取到meta data的。
所以这样来看onFrameAbailable都不会得到通知。(我相信是我手里的这版代码的问题啦)
之前我们说过QCam HAL有部分东西没有实现，所以mFrameQueue就不会有数据，但是它本来应该是DRV回来的元数据会queue到这里面。
另外
CaptureSequencer.h还有去实现onCaptureAvailable，当JpegProcessor处理完了会通知它。
好奇？多个stream(s)不是同时返回的，这样如果CPU处理快慢不同就会有时间差？还有很好奇DRV是如何处理Video snapshot的，如果buffer是顺序的，就会存在Video少一个frame，如果不是顺序的，那就是DRV一次返回多个buffer？以前真没有想过这个问题@_@
請問一下，若已經編譯出這個 hal 層，如何才能讓上層 camera APP 使用 UVC camera?
需要設定 setprop 什麼值嗎？
楼主，请问你对2.0的研究有没有进一步深入？在你这篇文章中提到的channel和stream，按我的理解是：channel对应具体的硬件设备，所以只有一个；而stream是对物理数据的引用，所以最多可以有8个。这种设计方式在实际应用场景中，可以让不同的应用(最多8个不同进程)使用同一个硬件的数据，而不会产生相互影响。我的理解是否正确，请指教。谢谢！
不好意思，各位，现在弄Audio相关的了，很久没有看过Camera，暂时没有办法解答各位的疑惑