[PATCH RFC 0/4] iommu/arm-smmu-v3: Support shared Stream IDs

[Peng Fan (OSS)]

Some SoCs have a limited number of IOMMU Stream IDs (SIDs) and
hardware that inherently shares them. For example, the NXP i.MX95
eDMA controller has 64 channels where each TX/RX pair is assigned
a single SID by the hardware - the two channel devices are distinct
from Linux's perspective but present the same SID to the SMMU.

The current ARM SMMUv3 driver rejects this with:
  "Aliasing StreamID unsupported, expect DMA to be broken"

I took comments in [1] and implement this patchset and only want to
support a very simple case that multiple platform devices share one SID.

This series adds support for multiple masters to share a single
SID, allowing per-channel DMA devices behind an IOMMU without
requiring one SID per channel.

Patch 1 converts the streams RB tree to an XArray for O(1) SID
lookup, simplifying duplicate-SID handling.

Patch 2 adds reference counting to streams so that multiple
masters can share a SID. Insert increments the refcount; remove
either transfers ownership or decrements. A per-SID linked list
tracks co-sharing masters.

Patch 3 places devices that share a SID into the same IOMMU
group, ensuring they share a single IOMMU domain.

Patch 4 wires up STE write ordering (first master writes, last
master tears down) and gates features that require unambiguous
SID-to-device mapping: SVA, IOPF/stall, and vSMMU nesting are
disabled for shared-SID masters.

[1] https://lore.kernel.org/linux-iommu/DU0PR04MB94172CB3F138AD39E9B6DEEF887F9@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
---
Peng Fan (4):
      iommu/arm-smmu-v3: Convert streams from RB tree to XArray
      iommu/arm-smmu-v3: Support shared SIDs in insert/remove_master
      iommu/arm-smmu-v3: Group aliasing devices into the same IOMMU group
      iommu/arm-smmu-v3: Wire up shared-SID STE ordering and feature gating

 .../iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c    |   4 +-
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c    |   7 +
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c        | 265 ++++++++++++++++-----
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h        |  34 ++-
 4 files changed, 247 insertions(+), 63 deletions(-)
---
base-commit: e6e35979777d646fe3c7c94dca7dd32fb25d45f4
change-id: 20260916-smmu-shared-sid-e488f6c4d4f0

Best regards,
--  
Peng Fan <peng.fan@xxxxxxx>