Re: [PATCH v5 3/3] iommu/arm-smmu-v3: Enable CFGI/TLBI-repeat workaround on Tegra264

[Nicolin Chen]

On Thu, Jul 09, 2026 at 09:56:09AM +0000, Ashish Mhetre wrote:
> Nvidia Tegra264 SMMU is affected by an erratum where a TLB entry can
> survive an invalidation that races with concurrent traffic targeting
> the same entry. The hardware-recommended software workaround is to
> issue every CFGI/TLBI command (each followed by CMD_SYNC) twice, and
> that infrastructure is already in place behind
> arm_smmu_erratum_repeat_tlbi_cfgi_key.
> 
> Neither IDR nor IIDR flags this Tegra264-specific bug, so hardware
> detection is not possible. Tegra264 is device-tree-only (no ACPI/IORT
> support) and already has a dedicated "nvidia,tegra264-smmu" compatible,
> so DT-probe is the only viable detection path.
> 
> Enable the workaround on instances matching the existing
> "nvidia,tegra264-smmu" compatible by calling static_branch_enable() on
> arm_smmu_erratum_repeat_tlbi_cfgi_key. Document the erratum in
> Documentation/arch/arm64/silicon-errata.rst.
> 
> Signed-off-by: Ashish Mhetre <amhetre@xxxxxxxxxx>

Reviewed-by: Nicolin Chen <nicolinc@xxxxxxxxxx>

Sashiko pointed out a concern at PATCH-3 regarding the static key:
https://sashiko.dev/#/patchset/20260709095613.831769-1-amhetre%40nvidia.com

It's a false positive. But perhaps we could fold in an inline note;
it'd belong to the missing description that I commented in PATCH-2.

Nicolin