Re: [PATCH v4 1/6] iommu/arm-smmu-v3: Support IDR5.DS and widen the TLBI SCALE field

[Jason Gunthorpe]

On Tue, Jul 14, 2026 at 11:48:47AM -0700, Nicolin Chen wrote:
> An SMMU implementing SMMU_IDR5.DS extends the range invalidation commands:
> the SCALE field grows a 6th bit, raising its maximum value from 31 to 39,
> and TTL == 0b01 becomes a valid level hint for a 16KB translation granule.
> 
> Add a new ARM_SMMU_FEAT_DS feature detecting the DS bit, and widen the
> CMDQ_TLBI_0_SCALE field to its architectural 6 bits. Mask the scale value
> explicitly in arm_smmu_cmdq_batch_add_range(), so the range invalidation
> path emits the same commands as before, keeping the pre-existing 5-bit
> truncation of a scale above 31.
> 
> Also list DS as a valid IDR5 field in the iommu_hw_info_arm_smmuv3 kdoc:
> iommufd has always reported the raw IDR5 register, so a VMM may conclude
> from that bit alone that it can expose DS to its guest.
> 
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Fixes: d68beb276ba2 ("iommu/arm-smmu-v3: Support IOMMU_HWPT_INVALIDATE using a VIOMMU object")
> Cc: stable@xxxxxxxxxxxxxxx # needed by the subsequent fix

I think you don't include these tags, the stable maintainers seem to
figure it out with scripts when things don't compile, as the next
patch wouldn't compile..

> Assisted-by: Claude:claude-fable-5
> Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 4 +++-
>  include/uapi/linux/iommufd.h                | 4 ++--
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 6 +++++-
>  3 files changed, 10 insertions(+), 4 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason