Working Linux OpenCL Driver

I tried to install both, the ATI and the Nvidia OpenCL-drivers on an intel-laptop with intel-onboard-graphics, but none worked, although they should.
Did someone try this with success?

None of the intel-onboard-graphics chips support OpenCL. With the AMD CPU driver you should be able to get the CPU device. The Nvidia/AMD drivers only support their respective Nvidia/AMD GPUs.

Thats clear. I only want to use the CPU. The driver didn’t work for me.