Re: [RFC PATCH 0/2] cpufreq/amd-pstate: Fixes for "Requested CPU Min frequency" support

[Mario Limonciello <mario.limonciello@amd.com>]

On 7/15/26 02:48, K Prateek Nayak wrote:
> It was noted during internal testing that amd-pstate active mode with
> performance governor always sets the min_perf to nominal_perf despite
> BIOS having supplied bios_min_perf as the preferred idling perf.
> 
> Users who set the "Requested CPU Min frequency" from BIOS are known to
> have profiled their workload at different operating frequency to know
> the best configuration and amd-pstate should use the same as the lower
> limit when configured.
> 
> While testing the fix for above, it was noted that kexec fails to
> persist bios_min_freq even when both, the old and new kernel are aware
> of bios_min_perf.
> 
> The suspend, offlining paths switched to persisting the CPPC_REQ MSR
> state at the time of suspend / offlining with only min_perf being reset
> to bios_min_perf.
> 
> msr_init() path only accepts the configured min_perf as bios_min_perf
> when it finds rest of the bits in CPPC_REQ MSR to be 0. This is
> intentional to prevent stale value of last CPPC_REQ from kernels that
> are not aware of bios_min_perf to be mistakenly interpreted as the
> bios_min_perf during kexec boot.

Is it a real valid case we need to worry about for someone kexec'ing 
between kernels that are aware of this vs not aware of it?

During kernel development; sure this might happen.  But I would think 
once this is available in mainline any of the distro kernels will have 
picked this up and people will start with a distro kernel with support, 
or they'll start with a distro kernel without and upgrade to one with.

I can't imagine a case people will go the other way.

> 
> Work around this limitation by stashing the state of CPPC_REQ during
> suspend / offlining in cpudata and then only programming the
> bios_min_perf into CPPC_REQ while keeping the rest of the bits as 0.
> 
> Resume / onlining callbacks use the stashed state to restore the
> CPPC_REQ before the CPU resumes normal operation.
> 
> Patches are prepared on top of linux-pm:bleeding-edge at commit
> 0e4eef86f0f4d ("Merge branch 'thermal-intel' into bleeding-edge").
>