Add a comprehensive debugfs framework to the ARM SMMUv3 driver,
providing visibility into internal hardware state for debugging
and performance analysis. The debugfs entries are organized under
/sys/kernel/debug/iommu/arm_smmu_v3/, with per-SMMU instance directories
and per-device stream table entries.

Each SMMU instance provides:
- capabilities – static SMMU features and queue sizes.
- registers – SMMU key registers.
- stream_table/ – a directory per device with subdirectories per Stream ID.

Each Stream ID subdirectory contains:
- ste – the Stream Table Entry in decoded and raw format.
- cd – all valid Context Descriptors (Stage 1 translation tables) associated with the device.
- a symlink named with the device's BDF/name pointing to its sysfs directory for easy navigation.

/sys/kernel/debug/iommu/arm_smmu_v3/smmu0/stream_table/
    ├── <sid>/
    │   ├── ste
    │   ├── cd
    │   └── <dev_name>

Changes since RFCv2:
  Address review comments from Nicolin Chen, kernel test robot, and Sashiko
  automated review:

  Build & kerneldoc fixes (patches 1-3):
   - Add missing @unused parameter description to kerneldoc comments to fix
     clang W=1 warnings reported by kernel test robot.
   - Fix commit message: "driver.This" -> "driver. This" (patch 1).

  Correctness fixes:
   - Fix integer overflow: 1 << sid_bits -> 1ULL << sid_bits with %llu format,
     preventing undefined behavior when SIDSIZE = 32 (patch 1).
   - Fix EVTQ register access: use smmu->page1 instead of smmu->base for
     EVTQ_PROD/EVTQ_CONS, which reside in register page 1 (patch 2).
   - Fix STE config bit test: use proper cfg comparison instead of bitwise AND
     on non-mask enumeration values, and extract S1ContextPtr from data[0]
     instead of data[1] (patch 3).

  Resource leak fixes (patches 1-5):
   - Fix device reference leak: call put_device() when single_open() fails in
     all open() callbacks (capabilities, registers, ste, cd).
   - Fix dentry reference leak: add missing dput() after debugfs_lookup() in
     stream table remove path (patch 3).
   - Move kobject_get_path() outside the per-stream loop to avoid repeated
     allocation (patch 4).

  Locking & concurrency fixes:
   - arm_smmu_debugfs_remove(): use scoped_guard() and move
     debugfs_remove_recursive() outside the lock to avoid blocking other SMMU
     instances on active VFS operations (patch 1).
   - smmu_debugfs_ste_show(): change scoped_guard to guard(mutex) since the
     entire function body is within the lock scope (patch 3).
   - smmu_debugfs_cd_show(): change manual mutex_lock/unlock to
     guard(mutex)(&arm_smmu_asid_lock) (patch 5).

  Error handling fixes:
   - Replace if (!debugfs_create_dir(...)) with IS_ERR() checks throughout,
     since debugfs_create_dir() returns ERR_PTR on failure, not NULL
     (patches 1, 3).
   - Add NULL check for smmu->debugfs before dereference in stream table
     create path (patch 3).
   - Add NULL check for kzalloc_obj() result (patch 3).

  Code style & cleanup:
   - Directory tree comment: use ├── for last entry to avoid churn on
     subsequent patches (patches 1-5).
   - Fix tab/space alignment in directory tree comments (patches 1, 2).
   - Reorder function parameters: @smmu first, @dev second (patch 3).
   - Fix return statement indentation (patch 3).
   - Move function declarations from #ifndef-static pattern to header file
     (patch 3).
   - Move char name[32] and snprintf() to function top for reuse by
     iommu_device_sysfs_add() regardless of CONFIG_ARM_SMMU_V3_DEBUGFS
     (patch 1).
   - Adopt non-tab-aligned style for new struct members (patches 1, 3).
   - Remove useless comments: "DebugFS Info" and "Reserved for future
     extensions" (patches 1, 3).
   - Remove spurious blank line (patch 3).

- Link: https://lore.kernel.org/all/20260328101706.3448655-1-xiaqinxin@huawei.com/

Qinxin Xia (5):
  iommu/arm-smmu-v3: Add basic debugfs framework
  iommu/arm-smmu-v3: Add register display to debugfs
  iommu/arm-smmu-v3: Add Stream Table Entry display to debugfs
  iommu/arm-smmu-v3: Add device symlink in stream table debugfs
  iommu/arm-smmu-v3: Add Context Descriptor display to debugfs

 drivers/iommu/Kconfig                              |  11 +
 drivers/iommu/arm/arm-smmu-v3/Makefile             |   1 +
 .../iommu/arm/arm-smmu-v3/arm-smmu-v3-debugfs.c    | 609 +++++++++++++++++++++
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c        |  27 +-
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h        |  30 +
 5 files changed, 675 insertions(+), 3 deletions(-)
 create mode 100644 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-debugfs.c

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2.51.0