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PC Processors

m_ozin
Journeyman III

AMD P-state & CPPC Problem in Linux - 3960X - Prime TRX40-Pro

Hello Everyone,

I have a Threadripper 3960X (Zen2) CPU with Asus Prime TRX40-Pro motherboard.

Although AMD says Zen2 processors support CPPC, it is not possible to activate this feature on TRX40 and Castle Peak CPUs.

I have checked several forums as well none so far activated this feature.

So, I did my research and my observations are below.

As we know Linux kernel uses standard implementation of ACPI.

CPPC can be declared either declared by either ACPI _OSC or CPUID intruction.

However, AMD CPUs declares CPPC via CPUID intruction.

However, cpuid 0x80000008 (ebx) CPPC bit is always 0 (disabled) whether you enable or disable CPPC in BIOS.

Asus AMI Bios does not have _OSC declaration for CPPC support in DSDT and SSDT tables.

There exists _CPC declarations in a SSDT table but since CPPC support is not declared, it is omitted by Linux kernel.

Hence, amd_pstate module declares "the _CPC object is not present in SBIOS or ACPI disabled"

Although acpi_cpufreq module works completely fine for these CPUs, there is a question in all TRX40 owner's mind who uses Linux:

Do TRX40 platform and Zen2 Threadripper CPUs really support the standard implementation of ACPI CPPC or is it just a "special feature" for Windows?

1 Solution
m_ozin
Journeyman III

UPDATE

A patch to Linux CPPC code is submitted by Perry Yuan from AMD in order to workaround this CPPC feature declaration problem and amd-pstate driver now works as expected.

For those who wants to apply the patch beforehand and benefit this feature can check the link below.

https://bugzilla.kernel.org/show_bug.cgi?id=218171

Problem is finally solved.

View solution in original post

3 Replies
gilvbp
Journeyman III

Same problem on Asus rampage ii zenith extreme (3970x)

m_ozin
Journeyman III

UPDATE

A patch to Linux CPPC code is submitted by Perry Yuan from AMD in order to workaround this CPPC feature declaration problem and amd-pstate driver now works as expected.

For those who wants to apply the patch beforehand and benefit this feature can check the link below.

https://bugzilla.kernel.org/show_bug.cgi?id=218171

Problem is finally solved.

thanks for the feedback. 

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