Thank you for contacting the Intel Communities.
I would like to recommend you to check with the manufacturer of your device if this could be enabled in your system's BIOS.
Reasoning: This is because the OEM or manufacturer of your device, is entitle to enable or disable what can be managed by the different tools you use with your computer.
The Intel® Extreme Tuning Utility communicates directly with the BIOS in your system, so chances are that options related to graphics are locked to be changed or managed by this utility.
If any additional questions or inquiries are present, feel free to contact us back.
I don't really think that restricting clocks is an OEM BIOS issue.
Intel SpeedStep is enabled, and that is really the only setting that needs to be ticked for this.
When adjusting the Intel Graphics CC settings, when set to "Maximum Battery Life", the GPU is restricted to 400 MHz, while at "Balanced" and "Maximum Performance" the GPU is allowed its full boost range (to 1 GHz). I believe this is also similar to how we can restrict the percentage of CPU clock in Power Options.
Thus, I assume software can restrict GPU clock rates, and if XTU cannot control it them it would be great to have a GPU limiter in Power Options or the Intel CC.
Sorry, but under Linux you can adjust the maximum clock of the GPU via the /sys/class/drm/card0/gt_max_freq_mhz.
Viewing the gt_cur_freq_mhz shows the current clock, and the above method does work.
However, linux does use the open-source Intel GPU driver (running Ubuntu 16.04), but this means it is not hardware related- I don't need an unlocked processor.