Re: [PATCH v3 1/9] arm64: Repaint ID_AA64MMFR2_EL1.IDS description

[Marc Zyngier <maz@kernel.org>]

On Thu, 04 Dec 2025 10:36:54 +0000,
Ben Horgan <ben.horgan@arm.com> wrote:
> 
> Hi Marc,
> 
> On 12/4/25 09:47, Marc Zyngier wrote:
> > ID_AA64MMFR2_EL1.IDS, as described in the sysreg file, is pretty horrible
> > as it diesctly give the ESR value. Repaint it using the usual NI/IMP
> > identifiers to describe the absence/presence of FEAT_IDST.
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/sys_regs.c | 2 +-
> >  arch/arm64/tools/sysreg            | 4 ++--
> >  2 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> > index 82da9b03692d4..107d62921b168 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> > @@ -134,7 +134,7 @@ static const struct pvm_ftr_bits pvmid_aa64mmfr2[] = {
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, UAO, IMP),
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, IESB, IMP),
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, AT, IMP),
> > -	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, 0x18),
> > +	MAX_FEAT_ENUM(ID_AA64MMFR2_EL1, IDS, IMP),
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, TTL, IMP),
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, BBM, 2),
> >  	MAX_FEAT(ID_AA64MMFR2_EL1, E0PD, IMP),
> > diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg
> > index 1c6cdf9d54bba..3261e8791ac03 100644
> > --- a/arch/arm64/tools/sysreg
> > +++ b/arch/arm64/tools/sysreg
> > @@ -2257,8 +2257,8 @@ UnsignedEnum	43:40	FWB
> >  	0b0001	IMP
> >  EndEnum
> >  Enum	39:36	IDS
> 
> Should this also be changed to an UnsignedEnum?

I'm not sure this brings much when you only have two values. If IDS
was growing a third value, and that there was an actual order in the
numbering scheme, then yes, that'd be useful.

But at this stage, I'm not confident that this is desirable, let alone
necessary.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.