Ivy Bridge-E CPU don't support xcpm natively

[BrushXue]

This is a follow up of #48. The processor ID issue is resolved. Now I can boot into the system with OC 0.6.6

From this page
https://dortania.github.io/OpenCore-Post-Install/universal/pm.html#enabling-x86platformplugin

Note: Ivy Bridge-E CPUs do officially support XCPM

My CPU is dual E5-2667 v2 and motherboard is C602. I should be able to activate xpcm. However it's not true in my case.
If I use SSDT-PLUG.aml, I'll get the following result:

X86PlatformPlugin::getCPUCStates - Unexpected data for C1
X86PlatformPlugin::getCPUPStates - C000 APSS and _PSS evaluations failed
X86PlatformPlugin::getCPUPStates - acpiPSArrayObj is not an valid OSArray
X86PlatformPlugin::publishAPICStates - Failed to get CPU P States!
X86PlatformPlugin::publishAPICStates - Failed to get max non-turbo PState. Set max non-turbo PState to default value 1

If I use ssdtPRGen, CPU power management will be available (X86PlatformPlugin is correctly loaded). But the frequency is always high (3.3GHz~4.0GHz) and never reach down to 1.2GHz.

[khronokernel]

Note: Ivy Bridge-E CPUs do officially support XCPM

Yeah this is actually incorrect on our part, Apple dropped Ivy Bridge E support with El Capitan and newer. So Mavericks and Yosemite would be the only OSes to support your hardware with XCPM.

Regarding ssdtPRGen creating unideal frequencies, that would need to be investigated further on your end. Acidanthera has an XCPM project for unsupported hardware, however we're unsure if this will ever be finished and released to the general public. I would say keep an eye out a few months from now and see if there's anything new in the world of XCPM

I'll leave this issue open, as I have been meaning to correct the XCPM info earlier in the guides

[BrushXue]

After some research, there's a BIOS option called P States Coordination, which only exists in server motherboards.
Changing it from HW_ALL to SW_ALL solves the high freq issue. Previously when idling it's floating between 3.3GHz~4.0GHz. Now it drops to 1.2GHz constantly. Please add this to HEDT config tutorial as a note.