core(ocl): add parameter to limit device max workgroup size

used by OpenCV

modules/core/src/ocl.cpp

@@ -1257,6 +1257,14 @@ struct Device::Impl
         else
             vendorID_ = UNKNOWN_VENDOR;
 
+        const size_t CV_OPENCL_DEVICE_MAX_WORK_GROUP_SIZE = utils::getConfigurationParameterSizeT("OPENCV_OPENCL_DEVICE_MAX_WORK_GROUP_SIZE", 0);
+        if (CV_OPENCL_DEVICE_MAX_WORK_GROUP_SIZE > 0)
+        {
+            const size_t new_maxWorkGroupSize = std::min(maxWorkGroupSize_, CV_OPENCL_DEVICE_MAX_WORK_GROUP_SIZE);
+            if (new_maxWorkGroupSize != maxWorkGroupSize_)
+                CV_LOG_WARNING(NULL, "OpenCL: using workgroup size: " << new_maxWorkGroupSize << " (was " << maxWorkGroupSize_ << ")");
+            maxWorkGroupSize_ = new_maxWorkGroupSize;
+        }
 #if 0
         if (isExtensionSupported("cl_khr_spir"))
         {