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T8x00/T9x00 P states bug (Aspire 7720G)

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I have bought a second hand Aspire 7720G (Inspyre bios) and upgraded the processor to a T9300 from a T7500. The processor is detected ok, but it turns out that the P States Frequencies (PSS fields) are not set ok and this makes Windows and Linux unable to downclock the processors using Speedstep. (Making my laptop very hot: 45C in Linux vs 32 with the T7500)

I tested with the Black 4.0 edition bios and also with the original Acer rom. I also edited both BIOSses with a hex editor to update the microcode to the latest version for this cpu. The upgrade works, but the ACPI data doesn't get written ok.

When I switch back to the T7500 everything goes ok. When I use the T9300 Linux complains about Firmware bug invalid PSS frequency 0x0Mhz, while reading the ACPI data in the kernel. It only keeps a single frequency 2.4 Ghz (while the proc is 2.5Ghz). When using the T7500 the cpufreq-info shows that there are 6 frequency steps available (800 - 2400 or so), the T9300 only shows one: 2.4Ghz.
In windows the T7500 auto downclocks (seen in HWINFO64), the T9300 keeps at 2.5Ghz. Clearly something is wrong. Using Throttlestop in Windows works, but in Linux there is no way to manually set the frequencies, or supply the correct values somehow. All the things I tried there had no effect.

I understand that this Inspyre bios from Acer calculates the frequencies instead of using tables with preset values, so I guess something goes wrong there with this newer generation of processors. (I also tested with a T8100, also the same issue).
Itś strange, because Acer sold these laptops also with T9300 processors themselves. I guess they screwed up.

Attached is the 1.45 Black Edition 4.0, without the microcode updates.

I would love to know if I can do anything about this, or if someone knows how to fix these frequency settings.

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