[PATCH RFC v2 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
only has 64 SIDs, only 6 bits for SID in the system chip bus.
However there are many device IPs, such as SDHC, PCIE, NETC, GPU,
NPU, Display, VPU, ISP, ISI, JPEG, SATA, DMA and etc. Each Kind IP has
mutilple instances inside the SoC. So I introudce this patchset to
support shared SID.

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.

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@DU0PR04MB9417.eurprd04.prod.outlook.com/

Signed-off-by: Peng Fan <peng.fan at nxp.com>
---
Changes in v2:
- Only update cover-letter to make it clear about why introducing shared
  SID
- Link to v1: https://patch.msgid.link/20260916-smmu-shared-sid-v1-0-517384504aee@nxp.com

---
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 at nxp.com>