Hi Suzuki,
On Tue, Nov 08, 2016 at 01:56:21PM +0000, Suzuki K. Poulose wrote:
> diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
> index 87b4465..4174f09 100644
> --- a/arch/arm64/include/asm/cpucaps.h
> +++ b/arch/arm64/include/asm/cpucaps.h
> @@ -34,7 +34,8 @@
> #define ARM64_HAS_32BIT_EL0 13
> #define ARM64_HYP_OFFSET_LOW 14
> #define ARM64_MISMATCHED_CACHE_LINE_SIZE 15
> +#define ARM64_HAS_NO_FPSIMD 16
>
> -#define ARM64_NCAPS 16
> +#define ARM64_NCAPS 17
>
> #endif /* __ASM_CPUCAPS_H */
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 9890d20..ce45770 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -213,6 +213,11 @@ static inline bool system_supports_mixed_endian_el0(void)
> return id_aa64mmfr0_mixed_endian_el0(read_system_reg(SYS_ID_AA64MMFR0_EL1));
> }
>
> +static inline bool system_supports_fpsimd(void)
> +{
> + return !cpus_have_const_cap(ARM64_HAS_NO_FPSIMD);
> +}
Any particular reason why using negation instead of a ARM64_HAS_FPSIMD?
A potential problem would be the default cpus_have_const_cap()
implementation and the default static key having a slight performance
impact.
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index fc2bd19..f89385d 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -746,6 +746,14 @@ static bool hyp_offset_low(const struct arm64_cpu_capabilities *entry,
> return idmap_addr > GENMASK(VA_BITS - 2, 0) && !is_kernel_in_hyp_mode();
> }
>
> +static bool has_no_fpsimd(const struct arm64_cpu_capabilities *entry, int __unused)
> +{
> + u64 pfr0 = read_system_reg(SYS_ID_AA64PFR0_EL1);
> +
> + return cpuid_feature_extract_signed_field(pfr0,
> + ID_AA64PFR0_FP_SHIFT) < 0;
> +}
> +
> static const struct arm64_cpu_capabilities arm64_features[] = {
> {
> .desc = "GIC system register CPU interface",
> @@ -829,6 +837,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
> .def_scope = SCOPE_SYSTEM,
> .matches = hyp_offset_low,
> },
> + {
> + /* FP/SIMD is not implemented */
> + .capability = ARM64_HAS_NO_FPSIMD,
> + .def_scope = SCOPE_SYSTEM,
> + .min_field_value = 0,
> + .matches = has_no_fpsimd,
> + },
If we go for negation, I don't think we need a min_field_value at all,
the matching is done by the has_no_fpsimd() function.
--
Catalin
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