MTK Android Camera运行流程
Android Camera 运行流程
总体架构
1.CameraService服务的注册
2.Client端的应用层到JNI层Camera App-JNI
3.Client到Service的连接
4.HAL层
5.驱动层
1.总体架构
Android Camera 框架从整体上看是一个 Client/Service 的架构,
有两个进程:
Client 进程,可以看成是 AP 端,主要包括 JAVA 代码与一些 native c/c++代码;
Service 进 程,属于服务端,是 native c/c++代码,主要负责和 linux kernel 中的 camera driver 交互,搜集 linuxkernel 中 cameradriver 传上来的数据,并交给显示系统显示。
Client 进程与 Service 进程通过 Binder 机制通信, Client 端通过调用 Service 端的接口实现各个具体的功能。
2.CameraService服务的注册
首先既然Camera是利用binder通信，它肯定要将它的Service注册到ServiceManager里面，以备后续Client引用，那么这一步是在哪里进行的呢？细心的人会发现，在frameworks\av\base\media\mediaserver\Main_MediaServer.cpp下有个main函数，可以用来注册媒体服务。CameraService完成了服务的注册,相关代码如下:
int main(int argc, char** argv)
{
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm = defaultServiceManager();
LOGI("ServiceManager: %p", sm.get());
AudioFlinger::instantiate();
MediaPlayerService::instantiate();
CameraService::instantiate();
AudioPolicyService::instantiate();
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
可是我们到CameraService文件里面却找不到instantiate()这个函数，它在哪？继续追到它的一个父类BinderService,
CameraService的定义在frameworks/av/base/Services/camera/libcameraService/CameraService.h中
class CameraService :
public BinderService<CameraService>,
public BnCameraService
{
class Client;
friend class BinderService<CameraService>;
public:
static char const* getServiceName() { return "media.camera"; }
.....
.....
}
从以上定义可以看出CameraService 继承于BinderService,所以CameraService::instantiate(); 其实是调用BinderService中的instantiate。
BinderService的定义在frameworks/av/base/include/binder/BinderService.h中
// ---------------------------------------------------------------------------
namespace android {
template<typename Service>
class BinderService
{
public:
static status_t publish() {
sp<IServiceManager> sm(defaultServiceManager());
return sm->addService(String16(Service::getServiceName()), new Service());
}
static void publishAndJoinThreadPool() {
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm(defaultServiceManager());
sm->addService(String16(Service::getServiceName()), new Service());
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
static void instantiate() { publish(); }
static status_t shutdown() {
return NO_ERROR;
}
};
}; // namespace android
// ---------------------------------------------------------------------------
可以发现在publish(）函数中，CameraService完成服务的注册 。这里面有个Service，源码中有说明
template<typename Service>
这表示Service是个模板，这里是注册CameraService，所以可以用CameraService代替
return sm->addService(String16(CameraService::getServiceName()), new CameraService());
这样，Camera就在ServiceManager完成服务注册，提供给Client随时使用。
Main_MediaServer主函数由init.rc在启动是调用，所以在设备开机的时候Camera就会注册一个服务，用作binder通信。
3.Client端的应用层到JNI层（Camera App--->JNI）
其调用流程图如下：
从第2节的分析中可知，Binder服务已注册，那接下来就看看Client如何连上server端，并打开camera模块。先从camera app的源码入手。在onCreate()函数中专门有一个open Camera的线程。
应用层
camera app的源码文件在以下目录packages/apps/LegacyCamera/src/com/android/camera/camera.java
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
getPreferredCameraId();
String[] defaultFocusModes = getResources().getStringArray(
R.array.pref_camera_focusmode_default_array);
mFocusManager = new FocusManager(mPreferences, defaultFocusModes);
/*
* To reduce startup time, we start the camera open and preview threads.
* We make sure the preview is started at the end of onCreate.
*/
mCameraOpenThread.start();
................
mCameraPreviewThread = null;
}
再看看mCameraOpenThread
Thread mCameraOpenThread = new Thread(new Runnable() {
public void run() {
try {
mCameraDevice = Util.openCamera(Camera.this, mCameraId);
} catch (CameraHardwareException e) {
mOpenCameraFail = true;
} catch (CameraDisabledException e) {
mCameraDisabled = true;
}
}
});
继续追Util.openCamera ,Util类的定义在以下目录:packages/apps/LegacyCamera/src/com/android/camera/Util.java
public static android.hardware.Camera openCamera(Activity activity, int cameraId)
throws CameraHardwareException, CameraDisabledException {
// Check if device policy has disabled the camera.
...............
try {
return CameraHolder.instance().open(cameraId);
} catch (CameraHardwareException e) {
// In eng build, we throw the exception so that test tool
// can detect it and report it
if ("eng".equals(Build.TYPE)) {
throw new RuntimeException("openCamera failed", e);
} else {
throw e;
}
}
}
又来了个CameraHolder，该类用一个实例open Camera
CameraHolder的定义在以下目录:packages/apps/LegacyCamera/src/com/android/camera/CameraHolder.java
public synchronized android.hardware.Camera open(int cameraId)
throws CameraHardwareException {
..............
if (mCameraDevice == null) {
try {
Log.v(TAG, "open camera " + cameraId);
mCameraDevice = android.hardware.Camera.open(cameraId);//进入framework层
mCameraId = cameraId;
} catch (RuntimeException e) {
Log.e(TAG, "fail to connect Camera", e);
throw new CameraHardwareException(e);
}
mParameters = mCameraDevice.getParameters();
} else {
............
}
++mUsers;
mHandler.removeMessages(RELEASE_CAMERA);
mKeepBeforeTime = 0;
return mCameraDevice;
}
其中调用frameworks\base\core\java\android\hardware\Camera.java类的open方法 ，进入Framework层。
Framework
其Framework层的open函数定义在如下文件中：frameworks\base\core\java\android\hardware\Camera.java
public static Camera open(int cameraId) {
return new Camera(cameraId);
}
这里调用了Camera的构造函数，对Camera类的一些参数进行简单初始化，其构造函数如下：
Camera(int cameraId) {
mShutterCallback = null;
mRawImageCallback = null;
mJpegCallback = null;
mPreviewCallback = null;
mPostviewCallback = null;
mZoomListener = null;
Looper looper;
if ((looper = Looper.myLooper()) != null) {
mEventHandler =new EventHandler(this, looper);
} else if ((looper = Looper.getMainLooper()) != null) {
mEventHandler = new EventHandler(this, looper);
} else {
mEventHandler = null;
}
native_setup(new WeakReference<Camera>(this), cameraId); //调用JNI
}
从这里开始通过JNI调用到native_setup( )，这里在系统上电时已经把JNI的一个对象注册成类Camer的Listener。
JNI层
native_setup( )接口在libandroid_runtime.so中实现，由Framework层通过JNI调用该接口。该接口主要是实现如下两个功能：
1、实现CameraC/S架构的客户端和服务端的连接（通过调用connect方法，进入libcamera_Client.so）
2、set一个监听类，用于处理底层Camera回调函数传来的数据和消息
native_setup()的定义在如下源文件中：frameworks/base/core/jni/android_hardware_Camera.cpp
static JNINativeMethod camMethods[] = {
{ "native_setup",
"(Ljava/lang/Object;I)V",
(void*)android_hardware_Camera_native_setup },
{ "startPreview",
"()V",
(void *)android_hardware_Camera_startPreview },
{ "native_autoFocus",
"()V",
(void *)android_hardware_Camera_autoFocus },
..................
};
通过这个定义,使得native_setup( )和android_hardware_Camera_native_setup( )关联起来。所以,native_setup(new WeakReference<Camera>(this), cameraId);这个调用即是对下面android_hardware_Camera_native_setup( )这个函数的调用:
// connect to camera Service
static voidandroid_hardware_Camera_native_setup(JNIEnv *env, jobject thiz,
jobject weak_this, jint cameraId)
{
sp<Camera> camera = Camera::connect(cameraId);
...........
// make sure camera hardware is alive
if (camera->getStatus() != NO_ERROR) {
jniThrowRuntimeException(env, "Camera initialization failed");
return;
}
...........
// We use a weak reference so the Camera object can be garbage collected.
// The reference is only used as a proxy for callbacks.
sp<JNICameraContext> context = new JNICameraContext(env, weak_this, clazz, camera);
context->incStrong(thiz);
camera->setListener(context);
// save context in opaque field
env->SetIntField(thiz, fields.context, (int)context.get());
}
JNI函数里面，我们找到Camera C/S架构的客户端了，它调用connect函数向服务器发送连接请求。JNICameraContext这个类是一个监听类，用于处理底层Camera回调函数传来的数据和消息。
4.Client到Service的连接
Clinet端
看看客户端的connect函数有什么? connenct()函数的实现在libcamera_Client.so中实现。它的源码在以下路径中：frameworks/av/camera/Camera.cpp
sp<Camera> Camera::connect(int cameraId)
{
LOGV("connect");
sp<Camera> c = new Camera();
const sp<ICameraService>& cs = getCameraService();//获取CameraService实例
if (cs != 0) {
c->mCamera = cs->connect(c, cameraId);
}
if (c->mCamera != 0) {
c->mCamera->asBinder()->linkToDeath(c);
c->mStatus = NO_ERROR;
} else {
c.clear();
}
return c;
}
其中通过const sp<ICameraService>& cs =getCameraService(); 获取CameraService实例，进入getCameraService( )中。
getCameraService( )源码文件如下：frameworks/av/camera/Camera.cpp
// establish binder interface to camera Service
const sp<ICameraService>& Camera::getCameraService()
{
Mutex::Autolock _l(mLock);
if (mCameraService.get() == 0) {
sp<IServiceManager> sm = defaultServiceManager();
sp<IBinder> binder;
....................
binder->linkToDeath(mDeathNotifier);
mCameraService = interface_cast<ICameraService>(binder);
}
LOGE_IF(mCameraService==0, "no CameraService!?");
return mCameraService;
}
CameraService实例通过binder获取的，mCameraService即为CameraService的实例。
Service端
Service端的实现在库libcameraService.so中。
回到sp<Camera> Camera::connect(int cameraId)中
c->mCamera = cs->connect(c, cameraId);
即：执行Service的connect（）函数，并且返回ICamera对象，赋值给Camera的mCamera，服务端connect（）返回的是他内部类的一个实例。
Service的connect（）函数定义库文件libcameraService.so中实现。
connect( )源码路径:frameworks/av/Services/camera/libcameraService/CameraService.cpp
sp<ICamera> CameraService::connect(
const sp<ICameraClient>& cameraClient, int cameraId) {
int callingPid = getCallingPid();
sp<CameraHardwareInterface> hardware = NULL;
....................
hardware = new CameraHardwareInterface(camera_device_name);
if (hardware->initialize(&mModule->common) != OK) {
hardware.clear();
return NULL;
}
Client = new Client(this, cameraClient, hardware, cameraId, info.facing, callingPid);
mClient[cameraId] = Client;
LOG1("CameraService::connect X");
return Client;
}
首先实例化Camera Hal接口 hardware，然后hardware调用initialize()进入HAL层打开Camear驱动。最后new Client（）返回给Client端。
5.HAL层
在Service端通过调用initialize()进入HAL层打开Camear驱动。initialize()的实现在CameraHardwareInterface中，其源码如下：
frameworks/av/Services/camera/libcameraService/CameraHardwareInterface.h
status_t initialize(hw_module_t *module)
{
LOGI("Opening camera %s", mName.string());
int rc = module->methods->open(module, mName.string(), (hw_device_t **)&mDevice);
if (rc != OK) {
LOGE("Could not open camera %s: %d", mName.string(), rc);
return rc;
}
initHalPreviewWindow();
return rc;
}
此处通过module->method->open()方法真正打开Camera设备,其中module是由它的调用者(serivce端：hardware->initialize(&mModule->common) )传过来的参数。该module的定义在以下路径:frameworks/av/Services/camera/libcameraService/CameraHardwareInterface.h
class CameraService :
public BinderService<CameraService>,
public BnCameraService
{
class Client : public BnCamera
{
public:
......
private:
.....
};
camera_module_t *mModule;
};
此处还必须找到camera_module_t 的定义,以更好的理解整个运行流程,通过追根溯源找到了camera_module_t 定义,
camera_module_t的定义在以下路径:hardware/av/include/hardware/camera_common.h中,定义如下
typedef struct camera_module {
hw_module_t common;
int (*get_number_of_cameras)(void);
int (*get_camera_info)(int camera_id, struct camera_info *info);
} camera_module_t;
其中包含get_number_of_cameras方法和get_camera_info方法用于获取camera info
另外hw_module_t common;这个选项十分重要,此处应重点关注,因为是使用hw_module_t结构体中的open()方法打开设备文件的
继续找到hw_module_t 结构体的定义。在以下路径:hardware/libhardware/include/hardware/hardware.h,代码如下:
struct hw_module_t;
struct hw_module_methods_t;
struct hw_device_t;
/**
* Every hardware module must have a data structure named HAL_MODULE_INFO_SYM
* and the fields of this data structure must begin with hw_module_t
* followed by module specific information.
*/
typedef struct hw_module_t {
......................
/** Modules methods */
struct hw_module_methods_t* methods;
......................
} hw_module_t;
同样,找到hw_module_methods_t这个结构体的定义,代码如下:
typedef struct hw_module_methods_t {
/** Open a specific device */
int (*open)(const struct hw_module_t* module, const char* id, struct hw_device_t** device);
} hw_module_methods_t;
hw_module_methods_t 结构体中只有open()一个方法,用于打开camera driver,实现与硬件层的交互。
open()是一个函数指针，对open()赋值的代码如下：/hardware/qcom/camera/QualcommCamera.cpp
static hw_module_methods_t camera_module_methods = {
open:camera_device_open,
};
其中camera_device_open()函数调用流程如下：
上图可知，在HAL层的module->methods->open(module, mName.string(), (hw_device_t **)&mDevice)回调，最终会调用到函数mm_camera__epen()。
int32_t mm_camera_open(mm_camera_obj_t *my_obj, mm_camera_op_mode_type_t op_mode)
{
.......................................
snprintf(dev_name, sizeof(dev_name), "/dev/%s", m_camera_util_get_dev_name(my_obj));
do{
n_try--;
my_obj->ctrl_fd = open(dev_name,O_RDWR | O_NONBLOCK);
...................
}while(n_try>0);
....................
return rc;
}
这个将调用系统调用open()的方法，打开设备节点dev/video0（后置相机），/dev/video2（前置相机），这个顺序是和内核在启动的是和
video的注册顺序相关的。
注意：这里的系统调用open（）函数是应用层的，它最终对应内核层（驱动）的open函数为msm_open(),如下：
/kernel/drivers/media/video/msm/msm.c
static struct v4l2_file_operations g_msm_fops = {
.owner = THIS_MODULE,
.open = msm_open,
.poll = msm_poll,
.mmap = msm_mmap,
.release = msm_close,
.ioctl = video_ioctl2,
};
msm_open()具体分析见第6节驱动层。
回到前面，设备节点dev/video0（后置相机），/dev/video2（前置相机）这个节点是在哪儿注册的呢？
6.驱动层
该节对摄像头驱动层进行分析，以高通平台为例。
/dev/目录下的摄像头注册是由驱动程序完成，在函数msm_cam_dev_ini( )中实现，源码在如下文件中：/kernel/drivers/media/video/msm/msm.c
其中，video_reister_device()完成摄像头节点的注册。
pvdev->ops = &g_msm_fops,则是向应用层提供打开摄像头Sensor的接口函数。
源码如下：/kernel/drivers/media/video/msm/msm.c
HAL层的open方法最终会调用的内核驱动层的msm_open()函数。
msm_open()源码文件为：/kernel/drivers/media/video/msm/msm.c
static int msm_open(struct file *f)
{
......................
/* Now we really have to activate the camera */
D("%s: call mctl_open\n", __func__);
rc = pmctl->mctl_open(pmctl, MSM_APPS_ID_V4L2);//打开相机
if (rc < 0) {
pr_err("%s: HW open failed rc = 0x%x\n", __func__, rc);
goto mctl_open_failed;
}
pmctl->pcam_ptr = pcam;
........................
if (pcam->use_count == 1) {
rc = msm_send_open_server(pcam);//后面进行分析
...............
}
........................
}
msm_send_openserver()在后面进行分析。
msm_open()调用mctl_open()，mctl_open()是真正打开相机的地方，当时它同样是一个函数指针，对该函数指针进行赋值在文件/kernel/drivers/media/video/msm/msm_mctl.c中，如下：
/* this function plug in the implementation of a v4l2_subdev */
int msm_mctl_init(struct msm_cam_v4l2_device *pcam)
{
...........
/* init module operations*/
pmctl->mctl_open = msm_mctl_open;
pmctl->mctl_cmd = msm_mctl_cmd;
pmctl->mctl_release = msm_mctl_release;
...........
}
msm_mctl_open()的源码在如下文件中：/kernel/drivers/media/msm/msm_mctl.c
static int msm_mctl_open(struct msm_cam_media_controller *p_mctl, const char *const apps_id)
{
..............................
/* then sensor - move sub dev later */
rc = v4l2_subdev_call(p_mctl->sensor_sdev, core, s_power, 1);
...............................
}
msm_mctl_open()函数调用v412_subdev_call( )，该函数中的s_power又是一个函数指针，通过回调调用函数msm_sensor_power（）,对该函数指针的赋值操作的源码如下：/kernel/drivers/media/video/msm/sensor/s5k4e1_v4l2.c
static struct v4l2_subdev_core_ops s5k4e1_subdev_core_ops = {
.ioctl = msm_sensor_subdev_ioctl,
.s_power = msm_sensor_power,
};
通过调用msm_sensor_power( )完成Camera的Sensor上电操作。
但是，此时camera并没有进行初始化，只是上电并读取ID而已，那么sensor又是在什么时候进行初始化的呢？继续进行分析............
在之前打开了/dev/video0 的节点，在 msm_open( ) 函数中，最后会去调用msm_send_open_server( ),这个函数会去唤醒我们用户空间的config 线程,msm_send_open_server( )源码如下：/kernel/drivers/media/video/msm/msm.c
/*send open command to server*/
static int msm_send_open_server(struct msm_cam_v4l2_device *pcam)
{
int rc = 0;
struct msm_ctrl_cmd ctrlcmd;
D("%s qid %d\n", __func__, pcam->server_queue_idx);
ctrlcmd.type = MSM_V4L2_OPEN;
ctrlcmd.timeout_ms = 10000;
ctrlcmd.length = strnlen(g_server_dev.config_info.config_dev_name[0],MAX_DEV_NAME_LEN)+1;
ctrlcmd.value = (char *)g_server_dev.config_info.config_dev_name[0];
ctrlcmd.vnode_id = pcam->vnode_id;
ctrlcmd.queue_idx = pcam->server_queue_idx;
ctrlcmd.config_ident = g_server_dev.config_info.config_dev_id[0];
/* send command to config thread in usersspace, and get return value */
rc = msm_server_control(&g_server_dev, &ctrlcmd);
return rc;
}
在这个函数中我们需要注意这个timeout的时间限制，它是要求我们的请求必须在10s内完成，否则config线程就会超时，从而导致相机将无法使用，只能通过重启来修复。
msm_server_control( )函数会向用户空间的config线程发送指令MSM_V4L2_OPEN(即代码中的ctrlcmd.type = SM_V4L2_OPEN)，这是用户空间的线程会被激活，调用用户空间的函数qcamsvr_process_server_node_event( ),源码如下：\vendor\qcom\proprietary\mm-camera\server\core\qcamsvr.c
static int qcamsvr_process_server_node_event( struct config_thread_arguments *config_arg,
struct msm_mctl_node_info *mctl_node_info, gesture_info_t *p_gesture_info)
{
..................................
if (ctrl->type == MSM_V4L2_OPEN) {
CDBG("MSM_V4L2_OPEN is received\n");
snprintf(config_arg->config_name, MAX_DEV_NAME_LEN, "%s",(char *)event_data.isp_data.ctrl.value);
CDBG("%s: OPEN %s\n", __func__, config_arg->config_name);
.........................
if ((tmp_mctl_struct->handle = create_v4l2_conf_thread(config_arg)) == NULL) {
CDBG_ERROR("%s: create_v4l2_conf_thread failed", __func__);
ctrl->status = CAM_CTRL_FAILED;
v4l2_ioctl.ioctl_ptr = ctrl;
goto error_config_thread_creation;
}
.........................
}
....................................
}
从以上代码可知，用户空间在这个地方收到了我们内核的请求后，接着会调用create_v4l2_conf_thread( )创建用户空间 config 线程。
现整个过程又回到用户空间..............
7.又见用户空间
在/dev/目录下有个设备节点文件./msm_camera/config0,即/dev/msm_camera/config0，这个文件的主要作用是打开它后，用它来完成Sensor的初始化。对于该节点主要关心两个问题：
①什么时候被创建？
在函数msm_camera_probe()，源码路径为：/kernel/drivers/media/msm/msm.c，主要是通过如下两条语句进行创建：
msm_class = class_create(THIS_MODULE, "msm_camera");
device_config = device_create(msm_class, NULL, devno,NULL, "%s%d",device_name, dev_num);//其中device_name = "config",dev_num = 0
②什么时候打开？具体分析见下。
由上面的分析可知，当内核驱动向用户空间发送SM_V4L2_OPEN请求，调用create_v4l2_conf_thread( )函数创建用户空间 config 线程，该函数的源码如下：\vendor\qcom\proprietary\mm-camera\server\core\mctl\mctl.c
void *create_v4l2_conf_thread(struct config_thread_arguments* arg)
{
.................................
rc = pthread_create(&pme->cam_mctl_thread_id, NULL, cam_mctl_thread, pme);
...........................
}
它创建一个线程，然后该线程执行的函数为cam_mctl_thread( )，然后它又调用mctl_init( ),即cam_mctl_thread( ) -----> mctl_init( )。mctl_init（）源码如下：
/vendor/qcom/proprietary/mm-camera/server/core/mctl/mctl.c
int mctl_init(m_ctrl_t* pme)
{
..........................
CDBG("%s: dev name is %s\n", __func__, config_device);
p_cfg_ctrl->camfd = open(config_device, O_RDWR);
..............................
mctl_proc_init_ops(p_cfg_ctrl);
s_comp_ops = &p_cfg_ctrl->comp_ops[MCTL_COMPID_SENSOR];
if(!s_comp_ops->handle) {
sensor_init_data_t sensor_init_data;
tmp_handle = sensor_Client_open(s_comp_ops);
...........................
}
.........
..........................
if (s_comp_ops->init) {
rc = s_comp_ops->init(s_comp_ops->handle, &p_cfg_ctrl->ops, &sensor_init_data);
.......................
}
....................................
}
open()函数打开/dev/camera/config0节点后，随后调用sensor_Client_open()函数，最有调用s_comp_ops->init()函数, 该函数利用config0节点去完成sensor的初始化工作。sensor_Client_open()完成函数指针_comp_ops->init()的赋值，源码如下:
/vendor/qcom/proprietary/mm-camera/server/hardware/sensor/sensor_interface.c
uint32_t sensor_Client_open(module_ops_t *ops)
{
.....................
ops->handle = (uint32_t)sensor_Client->handle;
ops->init = sensor_Client_init;
ops->set_params = sensor_Client_set_params;
ops->get_params = sensor_Client_get_params;
ops->process = NULL;
ops->abort = NULL;
ops->destroy= sensor_Client_destroy;
............................
}
因此，调用s_comp_ops->init()，实际是调用的函数sensor_Client_init()函数，然后该函数会调用到sensor_init()，
即s_comp_ops->init() --> sensor_Client_init() ---> sensor_init()。sensor_init( )的源码如下：
/vendor/qcom/proprietary/mm-camera/server/hardware/sensor/sensor.c
int8_t sensor_init(sensor_ctrl_t *sctrl)
{
struct msm_camsensor_info sinfo;
......................
sensor_common_parm_init(sctrl);
rc = ioctl(sctrl->sfd, MSM_CAM_IOCTL_GET_SENSOR_INFO, &sinfo);
........................
sctrl->start = &sensors[cnt];
rc = sctrl->start->s_start(sctrl);
if (sctrl->sensor.out_data.sensor_output.output_format == SENSOR_BAYER) {
rc = sensor_load_chromatix(sctrl);
........................
}
........................
}
在sensor_init()函数中，利用系统调用ioctl(),获取sensor的信息（包括sensor的类型yuv or raw，af enable ？ 闪光灯类型，sensor名等）。
其中：rc = sctrl->start->s_start(sctrl);
s_start()会调用s5k4e1_process_start(),对于函数指针s_start()的赋值，是用过一个宏定义进行的，具体参照文件/vendor/qcom/proprietary/mm-camera/server/hardware/sensor/sensor.c中的源码。
rc = sensor_load_chromatix(sctrl);
这条语句就会去加载我们的库文件了（仅仅针对RAW sensor）。
现分析函数s5k4e1_process_start()，源码如下：/vendor/qcom/proprietary/mm-camera/server/hardware/sensor/s5k4e1/s5k4e1_u.c
int8_t s5k4e1_process_start(void *ctrl)
{
sensor_ctrl_t *sctrl = (sensor_ctrl_t *) ctrl;
sctrl->fn_table = &s5k4e1_func_tbl;
sctrl->sensor.inputformat = s5k4e1_inputformat;
sctrl->sensor.crop_info = s5k4e1_cropinfo;
sctrl->sensor.mode_res = s5k4e1_mode_res;
sensor_util_get_output_info(sctrl);
sctrl->sensor.op_mode = SENSOR_MODE_VIDEO;
sctrl->sensor.out_data.sensor_output.connection_mode = SENSOR_MIPI_CSI;
sctrl->sensor.out_data.sensor_output.output_format = SENSOR_BAYER;
sctrl->sensor.out_data.sensor_output.raw_output = SENSOR_10_BIT_DIRECT;
sctrl->sensor.out_data.aec_info.max_gain = 16.0;
sctrl->sensor.out_data.aec_info.max_linecount = sctrl->sensor.output_info[sctrl->sensor.
mode_res[SENSOR_MODE_PREVIEW]].frame_length_lines * 24;
sctrl->sensor.snapshot_exp_wait_frames = 1;
sctrl->sensor.out_data.lens_info.focal_length = 3.49;
sctrl->sensor.out_data.lens_info.pix_size = 1.4;
sctrl->sensor.out_data.lens_info.f_number = 2.2;
sctrl->sensor.out_data.lens_info.total_f_dist = 1.97;
sctrl->sensor.out_data.lens_info.hor_view_angle = 54.8;
sctrl->sensor.out_data.lens_info.ver_view_angle = 42.5;
sensor_util_config(sctrl);
return TRUE;
}
其中：
sensor_util_get_output_info(sctrl);这条语句调用到内核获取长宽等
sensor_util_config(sctrl);这条语句调用到内核完成初始化
至此，整个摄像头open过程分析完成。
到此为止,很容易看出:
Android中Camera的调用流程可分为以下几个层次：
Package->Framework->JNI->Camera(cpp)--(binder)-->CameraService->Camera HAL->Camera Driver --> 通过消息内核驱动激活用户空间，完成Sensor初始化 ---> open完成http://blog.csdn.net/unicornkylin/article/details/13293295
