[PATCH v2 0/2] iommu/arm-smmu-v3: Tegra264 invalidation workaround

[Ashish Mhetre]

Nvidia Tegra264 SMMUs are 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. The
second issue must execute only after the first issue's CMD_SYNC has
completed, giving the sequence:

    TLBI/CFGI ... CMD_SYNC TLBI/CFGI ... CMD_SYNC

ATC_INV is not affected and must not be doubled.

This series implements the workaround by hooking the duplication into
the single chokepoint that every synchronous submission flows through,
arm_smmu_cmdq_issue_cmdlist().

Patch 1 detects affected instances using the existing
"nvidia,tegra264-smmu" compatible string and exposes the condition
via a new ARM_SMMU_OPT_TLBI_TWICE option bit.

Patch 2 wires the option into the CMDQ submission path: when @sync is
true and the cmdlist carries a CFGI/TLBI opcode, the same cmdlist is
re-issued a second time. The batch capacity-rollover path is also
adjusted to force a SYNC on chunks that carry CFGI/TLBI commands so
each flushed chunk is correctly doubled.

The series is based on Jason Gunthorpe's "Remove SMMUv3
struct arm_smmu_cmdq_ent" series [1], specifically commit 13428b0bf794
("iommu/arm-smmu-v3: Directly encode TLBI commands") which is the
final patch of that series in linux-next.

[1] https://lore.kernel.org/all/177919957385.1012282.14787407041669291032.b4-ty@xxxxxxxxxx/

Changes since v1:
- Patch 1: Add IIDR/IDR/ACPI rationale to the commit message, explaining
  why the erratum is detected from the device tree compatible string
  rather than from a HW register or ACPI/IORT.
- Rebased onto the publicly accessible base 13428b0bf794 (final commit
  of Jason's series in linux-next) so that the base-commit is resolvable
  on lore.kernel.org.
- Patch 2: Picked up Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>.
- No code changes since v1.


Ashish Mhetre (2):
  iommu/arm-smmu-v3: Detect Tegra264 erratum
  iommu/arm-smmu-v3: Issue CFGI/TLBI twice on Tegra264

 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 70 +++++++++++++++++++--
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  8 +++
 2 files changed, 72 insertions(+), 6 deletions(-)


base-commit: 13428b0bf7947098daf9a1db14a74d33eb1b5079
-- 
2.50.1