[PATCH v3 0/2] Add SMCCC cache clean/invalidate provider

[Srirangan Madhavan <smadhavan@nvidia.com>]

Apologies for the delay in posting v3. We waited until the corresponding
firmware support was available in TF-A. This allowed the provider to be
tested end to end with the CXL Reset series [2].

This series adds an arm64 backend for memregion cache invalidation users
based on the Arm SMCCC cache clean+invalidate interface.

Per DEN0028, this interface targets systems where a Normal Cacheable
memory region can be modified in ways that are not handled by usual PE
coherency mechanisms, and where VA-based CMOs may be too slow or
insufficient for large ranges and/or system-cache implementations.

Representative use cases include device-backed memory state transitions
where stale CPU/system cache lines must be invalidated reliably (for
example secure erase, reset/offline flows, and dynamic memory
reconfiguration).

Patch 1 introduces the Arm SMCCC cache clean/invalidate function IDs and
transient return codes needed by callers [1].

Patch 2 adds a cache maintenance provider that:
- discovers SMCCC support and attributes at init time
- registers with the generic cache coherency framework used by
  cpu_cache_invalidate_memregion()
- handles transient BUSY/RATE_LIMITED responses with bounded retries

This patch set does not add a software fallback path; when firmware does
not implement the SMCCC cache maintenance interface, the provider is not
registered and existing behavior is preserved.

References:
[1] https://developer.arm.com/documentation/den0028/h
[2] https://lore.kernel.org/linux-cxl/20260902072804.665639-1-smadhavan@nvidia.com/

DEN0028 v1.7 has since been confirmed as stable.

Testing:
- With corresponding TF-A support enabled, exercised the provider through
  the CXL Reset path and verified that it invokes the SMCCC call and
  completes the cache flush successfully.
- ARM64 defconfig with CONFIG_CACHEMAINT_FOR_HOTPLUG=y and
  CONFIG_ARM_SMCCC_CACHE=y
- W=1 build of drivers/cache/arm_smccc_cache.o
- W=1 build of the ARM64 Image

Changes since v2:
- Rebased onto Linux v7.3-rc1.
- Preserved the final BUSY or RATE_LIMITED error after retry exhaustion.
- Dropped the redundant feature query for the mandatory ATTRIBUTES call.
- Preserved the full 64-bit maximum-call-rate value returned in X3.
- Reordered local declarations in reverse-fir-tree order.
- Removed the routine provider registration message.

Changes since v1:
- Added Jonathan Cameron's Reviewed-by tags.
- Clarified the ARM_SMCCC_CACHE Kconfig help text.
- Added a Makefile comment identifying the providers that depend on
  CACHEMAINT_FOR_HOTPLUG.
- Dropped the final-backoff-sleep skip in the retry loop.

Changes since RFC:
- Dropped the RFC tag.
- Moved the provider from arch/arm64/mm to drivers/cache.
- Added a dedicated CONFIG_ARM_SMCCC_CACHE option under the existing
  CACHEMAINT_FOR_HOTPLUG menu.
- Dropped the global-operation coalescing optimization.
- Dropped provider handling for SMCCC_RET_NOT_REQUIRED.
- Removed the unnecessary global provider pointer.
- Removed arm64_ prefixes from static provider-local names.
- Documented why these SMCCC Arch cache maintenance calls use SMC64.
- Anchored the SMCCC return-code comment to DEN0028 v1.7.
- Used fsleep() for retry backoff.
- Used unsigned long for retry delay values passed to fsleep().
- Skipped the final backoff sleep when no retry remains.
- Documented the bounded mutex hold time across the serialized retry
  sequence.
- Added mutex_destroy() on the registration failure path.

Srirangan Madhavan (2):
  arm64: smccc: add cache clean/invalidate IDs and return codes
  cache: add SMCCC-backed cache invalidate provider

 drivers/cache/Kconfig           |  11 +++
 drivers/cache/Makefile          |   2 +
 drivers/cache/arm_smccc_cache.c | 149 ++++++++++++++++++++++++++++++++
 include/linux/arm-smccc.h       |  21 ++++-
 tools/include/linux/arm-smccc.h |  21 ++++-
 5 files changed, 200 insertions(+), 4 deletions(-)
 create mode 100644 drivers/cache/arm_smccc_cache.c


base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
-- 
2.43.0