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

[K Prateek Nayak]

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.

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").

-- 
K Prateek Nayak (2):
  cpufreq/amd-pstate: Set min_limit_freq based on bios_min_perf
  cpufreq/amd-pstate: Correctly reset bios_min_perf during suspend and
    offlining

 drivers/cpufreq/amd-pstate.c | 82 ++++++++++++++++++++++++++++--------
 1 file changed, 65 insertions(+), 17 deletions(-)


base-commit: 0e4eef86f0f4df58cb7526fdb968bb779fe66d81
-- 
2.34.1