[RFC PATCH 0/3] cxl: Auto-create a region for Type-2 memdev attach

[Richard Cheng <icheng@nvidia.com>]

A Type-2 accelerator driver calls devm_cxl_probe_mem() to register its
memdev and get an HPA range, but today only if FW already committed a
region. Real accelerators can have usable memory with no committed decoder,
so get nothing.

If no FW region is mapped, the core picks the device's unused manual
DEVMEM decoder and a compatible x1 Type-2 RAM root, allocates the full
volatile DPA and HPA, commits the decoder, and returns the range. Unbind
resets and removes it. Strict first cut with single decoder, IW=1, minimum
granularity, first-compatible root.

The design intent is that the provider F_LOCKs its region against userspace
but must reset its own software region on detach. A plain flag would also
allow reset on generic kill/delete paths, so we thread a reset context
through teardown and commit rollback. devm_cxl_probe_mem() may now commit
decoders.

Testing result is in the following.
- Built clean with clang/LLVM on arm64
- cxl_test, type2_test=1. accel0 takes the unchanged attach path. accel1
  drives auto_create -> a committed 512 MB RAM region. The test asserts
  the 512 MB HPA range. committed state and 256 byte granularity confirmed
  via sysfs.
- Unbind tears the region down with no orphaned decoder, rebind re-creates
  a fresh committed region.
- Mock test only. Real accelerators whose FW commits a decoder take the
  attach path, and vfio-cxl binds only FW-committed devices, so auto-create
  has no real-HW caller yet.

Best regards,
Richard Cheng.

Richard Cheng (3):
  cxl/region: Reset software-created regions on memdev detach
  cxl/region: Auto-create a region for memdev attach
  cxl/test: Exercise Type-2 automatic region creation

 drivers/cxl/core/region.c      | 422 +++++++++++++++++++++++++++++----
 tools/testing/cxl/test/accel.c |   7 +
 tools/testing/cxl/test/cxl.c   |  61 ++++-
 3 files changed, 439 insertions(+), 51 deletions(-)


base-commit: 1c6b4ceafc3b994871c29340e0c1ddb0af5800e7
-- 
2.43.0