[PATCH v2 0/6] iommu/arm-smmu: Add interconnect bandwidth voting support

[Bibek Kumar Patro]

On some Qualcomm SoCs the SMMU register space is gated behind an
interconnect fabric that requires an active bandwidth vote before
registers can be accessed. In the common case this vote is held
implicitly by other clients (e.g. the GMU device holds a GEM_NOC
vote whenever the GPU is active), so the SMMU works without any
explicit vote from the driver.

However, during certain power transitions — specifically sleep/wakeup
sequences — the interconnect vote can be dropped before the SMMU is
powered down. If the SMMU is then accessed (e.g. during runtime
resume) while the vote is absent, register reads fail intermittently.
The precise ordering makes this difficult to reproduce consistently.

This series adds support for an optional interconnect path in the
arm-smmu driver. When an 'interconnects' property is present in the
SMMU device node, the driver acquires the path and votes for bandwidth
before any register access, releasing the vote on runtime suspend and
on error paths. Platforms that do not describe an interconnect path
are unaffected.

Changes in v2:
- dt-bindings: Cleaned up 'interconnects' property description —
  removed "Optional" prefix and driver implementation details as
  flagged by Krzysztof Kozlowski.
- dt-bindings: Added allOf conditional using 'items' to restrict the
  'interconnects' property to Adreno SMMU nodes only (qcom,adreno-smmu
  with qcom,qcs615-smmu-500, qcom,qcs8300-smmu-500,
  qcom,sa8775p-smmu-500 or qcom,sc7280-smmu-500 compatible), so
  non-Adreno SMMU nodes on the same SoC cannot use this property.
- Added DTS patches for kodiak, lemans, monaco and talos to add
  the GEM_NOC interconnect path for the adreno_smmu node on each
  platform.
Link to v1:
https://lore.kernel.org/all/20260516-smmu_interconnect_addition-v1-0-f889d933f5c1@xxxxxxxxxxxxxxxx/

Signed-off-by: Bibek Kumar Patro <bibek.patro@xxxxxxxxxxxxxxxx>
---
Bibek Kumar Patro (6):
      dt-bindings: iommu: arm,smmu: Document interconnects property
      iommu/arm-smmu: Add interconnect bandwidth voting support
      arm64: dts: qcom: kodiak: Add GEM_NOC interconnect for adreno SMMU
      arm64: dts: qcom: lemans: Add GEM_NOC interconnect for adreno SMMU
      arm64: dts: qcom: monaco: Add GEM_NOC interconnect for adreno SMMU
      arm64: dts: qcom: talos: Add GEM_NOC interconnect for adreno SMMU

 .../devicetree/bindings/iommu/arm,smmu.yaml        | 27 ++++++++++
 arch/arm64/boot/dts/qcom/kodiak.dtsi               |  2 +
 arch/arm64/boot/dts/qcom/lemans.dtsi               |  2 +
 arch/arm64/boot/dts/qcom/monaco.dtsi               |  2 +
 arch/arm64/boot/dts/qcom/talos.dtsi                |  2 +
 drivers/iommu/arm/arm-smmu/arm-smmu.c              | 57 +++++++++++++++++++++-
 drivers/iommu/arm/arm-smmu/arm-smmu.h              |  2 +
 7 files changed, 92 insertions(+), 2 deletions(-)
---
base-commit: c1ecb239fa3456529a32255359fc78b69eb9d847
change-id: 20260516-smmu_interconnect_addition-d9567535e9d7

Best regards,
-- 
Bibek Kumar Patro <bibek.patro@xxxxxxxxxxxxxxxx>