On Thu, Aug 25, 2022 at 09:48:35AM -0700, Oliver Upton wrote:
> Hi Reiji,
>
> On Wed, Aug 24, 2022 at 10:08:38PM -0700, Reiji Watanabe wrote:
> > Introduce helpers to extract a field of an ID register.
> > Subsequent patches will use those helpers.
> >
> > Signed-off-by: Reiji Watanabe <reijiw@xxxxxxxxxx>
> > ---
> > .../selftests/kvm/include/aarch64/processor.h | 2 ++
> > .../testing/selftests/kvm/lib/aarch64/processor.c | 15 +++++++++++++++
> > 2 files changed, 17 insertions(+)
> >
> > diff --git a/tools/testing/selftests/kvm/include/aarch64/processor.h b/tools/testing/selftests/kvm/include/aarch64/processor.h
> > index a8124f9dd68a..a9b4b4e0e592 100644
> > --- a/tools/testing/selftests/kvm/include/aarch64/processor.h
> > +++ b/tools/testing/selftests/kvm/include/aarch64/processor.h
> > @@ -193,4 +193,6 @@ void smccc_hvc(uint32_t function_id, uint64_t arg0, uint64_t arg1,
> >
> > uint32_t guest_get_vcpuid(void);
> >
> > +int cpuid_get_sfield(uint64_t val, int field_shift);
> > +unsigned int cpuid_get_ufield(uint64_t val, int field_shift);
> > #endif /* SELFTEST_KVM_PROCESSOR_H */
> > diff --git a/tools/testing/selftests/kvm/lib/aarch64/processor.c b/tools/testing/selftests/kvm/lib/aarch64/processor.c
> > index 6f5551368944..0b2ad46e7ff5 100644
> > --- a/tools/testing/selftests/kvm/lib/aarch64/processor.c
> > +++ b/tools/testing/selftests/kvm/lib/aarch64/processor.c
> > @@ -528,3 +528,18 @@ void smccc_hvc(uint32_t function_id, uint64_t arg0, uint64_t arg1,
> > [arg4] "r"(arg4), [arg5] "r"(arg5), [arg6] "r"(arg6)
> > : "x0", "x1", "x2", "x3", "x4", "x5", "x6", "x7");
> > }
> > +
> > +/* Helpers to get a signed/unsigned feature field from ID register value */
> > +int cpuid_get_sfield(uint64_t val, int field_shift)
> > +{
> > + int width = 4;
> > +
> > + return (int64_t)(val << (64 - width - field_shift)) >> (64 - width);
> > +}
>
> I don't believe this helper is ever used.
>
> > +unsigned int cpuid_get_ufield(uint64_t val, int field_shift)
> > +{
> > + int width = 4;
> > +
> > + return (uint64_t)(val << (64 - width - field_shift)) >> (64 - width);
> > +}
>
> I would recommend not open-coding this and instead make use of
> ARM64_FEATURE_MASK(). You could pull in linux/bitfield.h to tools, or do
> something like this:
>
> #define ARM64_FEATURE_GET(ftr, val) \
> ((ARM64_FEATURE_MASK(ftr) & val) >> ftr##_SHIFT)
>
> Slight preference for FIELD_{GET,SET}() as it matches the field
> extraction in the kernel as well.
Was doing that with this commit:
[PATCH v5 05/13] tools: Copy bitfield.h from the kernel sources
Maybe you could just use it given that it's already reviewed.
>
> --
> Thanks,
> Oliver
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