[PATCH v5 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 is unchanged from v4 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 new in v5.  As Rafael pointed out, Sashiko observed that
the extract_msr() fallback interferes with 1/2 and can render it
ineffective: when the status read from the hardware matches no
freq_table entry, extract_msr() returns freq_table[0].frequency instead
of reporting the status as unknown.  If the OS is already at the P-state
corresponding to freq_table[0], a firmware switch to a filtered-out
P-state then compares equal to the cached frequency, data->resume is
left clear and the next ->target() call does not rewrite the control
register.  So 1/2 alone does not make the detection work in that case,
and the two patches are posted together rather than separately as I had
suggested earlier.

v4: https://lkml.iu.edu/2609.1/07369.html

Changes since v4:
 - Drop "cpufreq: acpi-cpufreq: fix P-state index mismatch in
   extract_io()", which has been applied.  This series is based on top
   of it.
 - Add 2/2 to stop extract_msr() from masking firmware P-state changes,
   as reported by Sashiko, and note the dependency in 1/2's changelog.
 - 1/2: no functional change; changelog extended to say that it fixes
   only the cached side of the comparison, and a duplicate
   Signed-off-by was removed.

Li RongQing (2):
  cpufreq: acpi-cpufreq: fix P-state index mismatch in
    get_cur_freq_on_cpu()
  cpufreq: acpi-cpufreq: don't mask firmware P-state changes

 drivers/cpufreq/acpi-cpufreq.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

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2.9.4