Re: [PATCH v2 6/6] arm64: cpufeature: Detect BBML3 based on MMFR2 ID

[Anshuman Khandual]

Please do mention full register field here

arm64: cpufeature: Detect BBML3 based on ID_AA64MMFR2_EL1.BBM

On 08/07/26 8:13 PM, Linu Cherian wrote:
> Add MMFR2 ID based BBML3 feature detection, so

Ditto ^^^^^^^^^^^^

> that compliant cpus doesn't need to be added to the
> midr list.

Could be reworded as :

Add ID_AA64MMFR2_EL1.BBM based BBML3 feature detection in
cpu_supports_bbml3() so that cpus with the feature would
not have to be added into MIDR based supports_bbml3_list.

> 
> Signed-off-by: Linu Cherian <linu.cherian@xxxxxxx>
> ---
>  arch/arm64/kernel/cpufeature.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index e9ecaa036479..3f4a36f152d0 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -2133,6 +2133,12 @@ static bool hvhe_possible(const struct arm64_cpu_capabilities *entry,
>  
>  bool cpu_supports_bbml3(void)
>  {
> +	u64 mmfr2;
> +
> +	mmfr2 = __read_sysreg_by_encoding(SYS_ID_AA64MMFR2_EL1);
> +	if (SYS_FIELD_GET(ID_AA64MMFR2_EL1, BBM, mmfr2) >= ID_AA64MMFR2_EL1_BBM_3)
> +		return true;
> +
>  	/* CPUs that support BBML3 but dont advertise through MMFR2 ID */
>  	static const struct midr_range supports_bbml3_list[] = {
>  		MIDR_REV_RANGE(MIDR_CORTEX_X4, 0, 3, 0xf),
> @@ -2153,15 +2159,10 @@ bool cpu_supports_bbml3(void)
>  		{}
>  	};
>  
> -	if (!is_midr_in_range_list(supports_bbml3_list))
> -		return false;
> -
> -	/*
> -	 * We currently ignore the ID_AA64MMFR2_EL1 register, and only care
> -	 * about whether the MIDR check passes.
> -	 */
> +	if (is_midr_in_range_list(supports_bbml3_list))
> +		return true;
>  
> -	return true;
> +	return false;
>  }
>  
>  static bool has_bbml3(const struct arm64_cpu_capabilities *caps, int scope)

With the minor changes to the commit message above.

Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>