Re: [PATCH 1/2] iommu/arm-smmu-v3: Detect Tegra264 erratum

[Nicolin Chen]

On Thu, May 28, 2026 at 09:36:34PM +0530, Ashish Mhetre wrote:
> On 5/28/2026 4:04 PM, Robin Murphy wrote:
> > On 2026-05-28 11:16 am, Ashish Mhetre wrote:
> > > Tegra264 SMMU is affected by 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. The second issue is
> > > guaranteed to evict the entry. ATC_INV is not affected and must not be
> > > doubled.
> > > 
> > > Add the ARM_SMMU_OPT_TLBI_TWICE option and set it on instances matching
> > > the existing "nvidia,tegra264-smmu" compatible. No callers consume the
> > > option yet, next patch wires the workaround into the CMDQ issue paths.
> > 
> > Can you not detect this implementation from IIDR like for our other
> > workarounds? Otherwise what about ACPI?
> 
> Neither IDR nor IIDR flags this Tegra264-specific bug. We cannot
> detect it from any HW register, so we have to rely on the Tegra264
> device tree.
> Regarding ACPI, the bug is in Tegra264 only, and Tegra264 is
> device-tree-only. It doesn't support ACPI/IORT as of now.

Let's add a note in the commit message.

Nicolin