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

[Linu Cherian]

Hi,

On Fri, Jul 10, 2026 at 12:41:57PM +0530, Anshuman Khandual wrote:
> 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.
> 

Okay, will change.


> > 
> > 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>