On 2022-10-27 17:09, Reiji Watanabe wrote:
I think that with this patch both PMUVer and Perfmon values get set to
0 (pmuver_to_perfmon() returns 0 for both ID_AA64DFR0_PMUVER_IMP_DEF
and no PMU at all). Am I missing anything here?
When pmuver_to_perfmon() returns 0 for ID_AA64DFR0_PMUVER_IMP_DEF,
cpuid_feature_cap_perfmon_field() is called with 'cap' == 0. Then,
the code in cpuid_feature_cap_perfmon_field() updates the 'val' with 0
if the given 'features' (sanitized) value is
ID_AA64DFR0_PMUVER_IMP_DEF.
So, now the val(== 0) is not larger than the cap (== 0), and
cpuid_feature_cap_perfmon_field() ends up returning the given
'features'
value as it is without updating the PERFMON field.
Ah, thanks for spelling it out for me, I was definitely looking
at the wrong side of things. You're absolutely right. The code
I have now makes sure to:
(1) preserve the IMP_DEF view of the PMU if userspace provides
such setting
(2) directly places the emulated PMU revision in the feature
set without calling cpuid_feature_cap_perfmon_field(),
which indeed does the wrong thing.
Hopefully I got it right this time! ;-)
Thanks again,
M.
--
Jazz is not dead. It just smells funny...
