如何在 kernel 和 hal 层读取同一个标志

很多时候我们需要从 HAL 层（Hardware Abstract Layer）传一个标志给 kernel 层。一般这种传递是不能直接通过定义全局变量来实现的。

此时可以通过读写文件来实现该标志。

譬如我们有这样一个需求，在录像过程中去掉持续对焦功能，而录像预览时开启持续对焦功能。

在 HAL 层中有开始录像和停止录像的接口。

/trunk/ALPS.JB3.TDD.MP.V2_TD_xxx/mediatek/platform/mt6572/hardware/camera/hal/client/CamClient/Record/RecordClient.cpp 文件中

在 /sys/devices/platform/lens_actuator/ 目录下创建一个 VideoRec_Flag 这样的文件，在开始录像时将该文件中写入一个字节的值为1，而在停止录像时将该文件中写入一个字节的值为0。

 bool
 RecordClient::
 startRecording()
 {
     bool ret = false;
     //
     MY_LOGD("+");
     //
     Mutex::Autolock _l(mModuleMtx);
     //
 #if 1
     int flag[]= {};  

     FILE *fd = NULL;
     fd = fopen("/sys/devices/platform/lens_actuator/VideoRec_Flag","w");  

     if(fd == NULL)
      MY_LOGD("BBN_TestMode open failed");
     else{
      MY_LOGD("BBN_TestMode open ok");
      fwrite(&flag,,,fd);
      fclose(fd);
     }
 #endif    

     if(isEnabledState())
     {
         MY_LOGE("Recording has been started");
         goto lbExit;
     }
     //
     MY_LOGD("+ current mIsRecStarted=%d", mIsRecStarted);
     ::android_atomic_write(, &mIsRecStarted);
     //
     mpParamsMgr->getVideoSize(&mi4RecWidth, &mi4RecHeight);
     MY_LOGD("+ record: WxH=%dx%d, format(%s)", mi4RecWidth, mi4RecHeight, MtkCameraParameters::PIXEL_FORMAT_YUV420I);//CameraParameters::PIXEL_FORMAT_YUV420P);
     //
     mTimeStart = systemTime();
     mTimeEnd = mTimeStart;
     mFrameCount = ;
     mLastTimeStamp = ;
     //
     ret = onStateChanged();
     //
 lbExit:
     //
     MY_LOGD("-");
     //
     return  ret;
 }  

 /******************************************************************************
  *
  ******************************************************************************/
 bool
 RecordClient::
 stopRecording()
 {
     bool ret = false;
     status_t status = NO_ERROR;
     //
     MY_LOGD("+");
     //
 #if 1
     int flag[]= {};  

     FILE *fd = NULL;
     fd = fopen("/sys/devices/platform/lens_actuator/VideoRec_Flag","w");  

     if(fd == NULL)
      MY_LOGD("BBN_TestMode open failed");
     else{
      MY_LOGD("BBN_TestMode open ok");
      fwrite(&flag,,,fd);
      fclose(fd);
     }
 #endif  

     Mutex::Autolock _l(mModuleMtx);
     //
     if(!isEnabledState())
     {
         MY_LOGE("Recording has been stopped");
         goto lbExit;
     }
     //
     MY_LOGD("getThreadId(%d), getStrongCount(%d), this(%p)", getThreadId(), getStrongCount(), this);
     //
     MY_LOGD("+ current mIsRecStarted=%d", mIsRecStarted);
     ::android_atomic_write(, &mIsRecStarted);
     //
     ret = onStateChanged();
     //
     mpImgBufQueue->pauseProcessor();
     //
 lbExit:
     //
     MY_LOGD("-");
     //
     return  ret;
 }  

在/trunk/ALPS.JB3.TDD.MP.V2_TD_xxx/mediatek/custom/common/kernel/imgsensor/ov5645_mipi_yuv/ov5645mipiyuv_Sensor.c 文件中

在 OV5645_FOCUS_OVT_AFC_Constant_Focus() 函数中读取之前VideoRec_Flag那个文件中的值，若为1，则进行持续对焦，否则，放弃持续对焦。在驱动文件中是通过写寄存器来实现的。

 static void OV5645_FOCUS_OVT_AFC_Constant_Focus(void)
 {
     printk("FM50AF_VideoRec_Flag=%d \n",FM50AF_VideoRec_Flag);  

    if(FM50AF_VideoRec_Flag)
    {
        OV5645MIPI_write_cmos_sensor(0x3023,0x01);
        OV5645MIPI_write_cmos_sensor(0x3022,0x06);
    }
    else{
         OV5645MIPI_write_cmos_sensor(0x3023,0x01);
         OV5645MIPI_write_cmos_sensor(0x3022,0x80);
         mDELAY();
         OV5645MIPI_write_cmos_sensor(0x3024,0x00);
         OV5645MIPI_write_cmos_sensor(0x3023,0x01);
         OV5645MIPI_write_cmos_sensor(0x3022,0x04);
     }
 }  

具体的读取方式如下：

 int FM50AF_VideoRec_Flag;  

 EXPORT_SYMBOL(FM50AF_VideoRec_Flag);  

 static ssize_t show_VideoRec_Flag(struct device *dev,struct device_attribute *attr, char *buf)
 {
 //  xlog_printk(ANDROID_LOG_DEBUG, "show_VideoRec_Flag test", "[Battery] show_BN_TestMode : %x\n", g_BN_TestMode);  

     printk("show_VideoRec_Flag FM50AF_VideoRec_Flag=%d \n",FM50AF_VideoRec_Flag);
     return sprintf(buf, "%u\n", FM50AF_VideoRec_Flag);  

 }
 static ssize_t store_VideoRec_Flag(struct device *dev,struct device_attribute *attr, const char *buf, size_t size)
 {
     char *pvalue = NULL;
     unsigned int reg_BN_TestMode = ;
     printk( "store_VideoRec_Flag \n");
     if(buf != NULL && size != )
     {
         printk("store_VideoRec_Flag test111", "[Battery] buf is =%s , size is =%d \n",buf,size);
         printk("store_VideoRec_Flag buf= %d ,size=%d \n", *buf,size);
     //  reg_BN_TestMode = simple_strtoul(buf,&pvalue,10);
         FM50AF_VideoRec_Flag=*buf;
     }
 //  return size;
 return FM50AF_VideoRec_Flag;
 }
 static DEVICE_ATTR(VideoRec_Flag, , show_VideoRec_Flag, store_VideoRec_Flag);  

这其中涉及到一些驱动文件中读写文件的格式的写法需要注意下。

至此，就可以实现该需求了。