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.
--
Thanks,
Oliver
