Re: [PATCH v10 1/3] arm64: cpufeature: introduce helper cpu_has_hw_af()

[Will Deacon]

On Mon, Sep 30, 2019 at 09:57:38AM +0800, Jia He wrote:
> We unconditionally set the HW_AFDBM capability and only enable it on
> CPUs which really have the feature. But sometimes we need to know
> whether this cpu has the capability of HW AF. So decouple AF from
> DBM by new helper cpu_has_hw_af().
> 
> Signed-off-by: Jia He <justin.he@xxxxxxx>
> Suggested-by: Suzuki Poulose <Suzuki.Poulose@xxxxxxx>
> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> ---
>  arch/arm64/include/asm/cpufeature.h | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index 9cde5d2e768f..949bc7c85030 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -659,6 +659,16 @@ static inline u32 id_aa64mmfr0_parange_to_phys_shift(int parange)
>  	default: return CONFIG_ARM64_PA_BITS;
>  	}
>  }
> +
> +/* Check whether hardware update of the Access flag is supported */
> +static inline bool cpu_has_hw_af(void)
> +{
> +	if (IS_ENABLED(CONFIG_ARM64_HW_AFDBM))
> +		return read_cpuid(ID_AA64MMFR1_EL1) & 0xf;

0xf? I think we should have a mask in sysreg.h for this constant.

Will