Small trick that may come in handy for others:
In my machine I have both a discrete nVidia GPU and an integrated GPU on the CPU. For some time I have wanted to use both in an OpenCL application, but until now I have not been able to access the iGPU as my primary (and only) monitor is attached to the nVidia card.
It turns out that the iGPU is turned off by default, but it is possible to force on in the BIOS. In my case (ASUS motherboard) it was done by accessing the advanced settings, then Graphics and then set
Primary display to "PCIe" (was Auto)
iGPU multi monitor to "On" (was off)
This turned on the iGPU even with no monitor attached, and triggered installataion of the Intel drives that enabled OpenCL.
I suppose similar settings may exist in other BIOS as well.
