[PATCH v6 0/2] cpufreq: acpi-cpufreq: fix P-state index mismatch between perf->states[] and freq_table[]

[lirongqing <lirongqing@baidu.com>]

From: Li RongQing <lirongqing@baidu.com>

policy->freq_table is built by filtering out _PSS entries that are not
lower in frequency than the previous one, and the original ACPI P-state
index of each remaining entry is kept in freq_table[].driver_data.  The
index spaces of perf->states[] and freq_table[] therefore differ, and
mixing them up leads to the frequency of one P-state being attributed to
another.

Patch 1/2 has no functional change from v5 and fixes the cached
frequency used by get_cur_freq_on_cpu() to detect a firmware frequency
change behind the OS's back.

Patch 2/2 is reworked.  In v5 it made extract_msr() return 0 for an
unmatched status and had get_cur_freq_on_cpu() set data->resume and
return the cached frequency instead.  As pointed out in the v5 review,
this cannot work: the returned value equals policy->cur, so
cpufreq_verify_current_freq() does not resynchronize policy->cur and
__cpufreq_driver_target() returns early before acpi_cpufreq_target()
can consume data->resume.  It also regressed the case where the OS is at
a lower P-state, which the old freq_table[0] fallback did get the core
to notice.

v6 instead lets extract_msr() look the status up in all of
perf->states[], so ->get() reports the real frequency of a filtered-out
P-state and the cpufreq core detects the mismatch itself.  The
freq_table[0] fallback is kept for a status that matches no _PSS entry,
and get_cur_freq_on_cpu() is left as in 1/2.

v5: <link to v5>

Changes since v5:
 - 1/2: no functional change; drop the changelog paragraph saying the
   extract_msr() fallback is addressed by the next patch.
 - 2/2: look the status up in perf->states[] instead of returning 0
   from extract_msr(); drop the get_cur_freq_on_cpu() change; new
   subject.
 - 2/2: changelog rewritten; drop the incorrect claim that the
   ACPI_ADR_SPACE_SYSTEM_IO path is covered, as ->get() is only
   registered for ACPI_ADR_SPACE_FIXED_HARDWARE.

Li RongQing (2):
  cpufreq: acpi-cpufreq: fix P-state index mismatch in
    get_cur_freq_on_cpu()
  cpufreq: acpi-cpufreq: report filtered-out P-states in extract_msr()

 drivers/cpufreq/acpi-cpufreq.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

-- 
2.9.4