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

["Bence Csókás" <bence.csokas@arm.com>]

Hi,

On 2026. 09. 10. 10:21, Srirangan Madhavan wrote:
> 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.

Reviewed-by: Bence Csókás <bence.csokas@arm.com>

I have yet to try it out on actual hardware, but from looking at the 
code, it now seems to match the spec.

> 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

Bence