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

On Thu, 04 Dec 2025 11:13:41 +0000,
Ben Horgan [off-list ref] wrote:

Hi Marc,

On 12/4/25 10:48, Marc Zyngier wrote:

quoted

On Thu, 04 Dec 2025 10:36:54 +0000,
Ben Horgan [off-list ref] wrote:

quoted

Hi Marc,

On 12/4/25 09:47, Marc Zyngier wrote:

quoted

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.

Joey just pointed out to me that there is a new third field. Not in the
arm reference manual yet, but mentioned in the xml. I'm unsure if it's
necessary to consider this at the moment though.

https://developer.arm.com/documentation/ddi0601/2025-09/AArch64-Registers/ID-AA64MMFR2-EL1--AArch64-Memory-Model-Feature-Register-2?lang=en

Ah, nice catch. In which case I agree that this should become
UnsignedEnum, as the new EL3 feature is a strict superset of 0b0001.

I'll add fix for that on top.

Thanks,

	M.

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