[PATCH v8 0/6] bits: Fixed-type GENMASK_U*() and BIT_U*()

[Vincent Mailhol via B4 Relay]

Introduce some fixed width variant of the GENMASK() and the BIT()
macros in bits.h. For example:

  GENMASK_U16(16, 0)

will raise a build bug.

This series is a continuation of:

  https://lore.kernel.org/intel-xe/20240208074521.577076-1-lucas.demarchi@intel.com

from Lucas De Marchi. Above series is one year old. I really think
that this was a good idea and I do not want this series to die. So I
am volunteering to revive it.

Meanwhile, many changes occurred in bits.h. The most significant
change is that __GENMASK() was moved to the uapi headers. For this
reason, a new GENMASK_TYPE() is introduced instead and the uapi
__GENMASK() is left untouched.

Finally, I do not think it makes sense to expose the fixed width
variants to the asm. The fixed width integers type are a C concept. So
the GENMASK_U*() are only visible to the non-asm code. For asm, the
long and long long variants seem sufficient.

This series does not modify the actual GENMASK(), GENMASK_ULL() and
GENMASK_U128(). A consolidation of the existing genmasks will be
proposed later on in a separate series.

As requested, here are the bloat-o-meter stats:

  $ ./scripts/bloat-o-meter vmlinux_before.o vmlinux_after.o 
  add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0 (0)
  Function                                     old     new   delta
  Total: Before=22781662, After=22781662, chg +0.00%

(done with GCC 12.4.1 on an x86_64_defconfig)

--
2.43.0

---
Changes from v7:

  - Meanwhile, in commit db6fe4d61ece ("lib: Move KUnit tests into
    tests/ subdirectory"), lib/test_bits.c was moved to
    lib/tests/test_bits.c. Rebase onto Linus's master branch so that
    this change is reflected.

  - Remove the note in the cover letter on the return type, instead
    add an explanation in patch "bits: introduce fixed-type
    GENMASK_U*()".

  - s/shift-count-overflow/-Wshift-count-overflow/g

  - Link to v7: https://lore.kernel.org/r/20250322-fixed-type-genmasks-v7-0-da380ff1c5b9@wanadoo.fr

Changes from v6:

  - Split the series in two: this series leave any existing GENMASK*()
    unmodified. The consolidation will be done in a separate series.

  - Collect some Reviewed-by tag.

  - Address miscellaneous nitpick on the code comments and the line
    wrapping (details in each patch).

  - Link to v6: https://lore.kernel.org/r/20250308-fixed-type-genmasks-v6-0-f59315e73c29@wanadoo.fr

Changes from v5:

  - Update the cover letter message. I was still refering to
    GENMASK_t() instead of GENMASK_TYPE().

  - Add a comment in the cover letter to explain that a common
    GENMASK_TYPE() for C and asm wouldn't allow to generate the u128
    variant.

  - Restore the comment saying that BUILD_BUG_ON() is not available in
    asm code.

  - Add a FIXME message to highlight the absence of the asm GENMASK*()
    unit tests.

  - Use git's histogram diff algorithm

  - Link to v5: https://lore.kernel.org/r/20250306-fixed-type-genmasks-v5-0-b443e9dcba63@wanadoo.fr

Changes from v4:

  - Rebase on https://github.com/norov/linux/tree/bitmap-for-next

  - Rename GENMASK_t() to GENMASK_TYPE()

  - First patch of v4 (the typo fix 'init128' -> 'int128') is removed
    because it was resent separately in:
    https://lore.kernel.org/all/20250305-fix_init128_typo-v1-1-cbe5b8e54e7d@wanadoo.fr

  - Replace the (t)~ULL(0) by type_max(t). This way, GENMASK_TYPE()
    can now be used to generate GENMASK_U128().

  - Get rid of the unsigned int cast for the U8 and U16 variants.

  - Add the BIT_TYPE() helper macro.

  - Link to v4: https://lore.kernel.org/r/20250305-fixed-type-genmasks-v4-0-1873dcdf6723@wanadoo.fr

Changes from v3:

  - Rebase on v6.14-rc5

  - Fix a typo in GENMASK_U128() comment.

  - Split the asm and non-asm definition of 

  - Replace ~0ULL by ~ULL(0)

  - Since v3, __GENMASK() was moved to the uapi and people started
    using directly. Introduce GENMASK_t() instead.

  - Link to v3: https://lore.kernel.org/intel-xe/20240208074521.577076-1-lucas.demarchi@intel.com

Changes from v2:

  - Document both in commit message and code about the strict type
    checking and give examples how it´d break with invalid params.

  - Link to v2: https://lore.kernel.org/intel-xe/20240124050205.3646390-1-lucas.demarchi@intel.com

Link to v1: https://lore.kernel.org/intel-xe/20230509051403.2748545-1-lucas.demarchi@intel.com

---
Lucas De Marchi (3):
      bits: introduce fixed-type BIT_U*()
      drm/i915: Convert REG_GENMASK*() to fixed-width GENMASK_U*()
      test_bits: add tests for GENMASK_U*()

Vincent Mailhol (3):
      bits: add comments and newlines to #if, #else and #endif directives
      bits: introduce fixed-type GENMASK_U*()
      test_bits: add tests for BIT_U*()

 drivers/gpu/drm/i915/i915_reg_defs.h | 108 ++++-------------------------------
 include/linux/bitops.h               |   1 -
 include/linux/bits.h                 |  57 +++++++++++++++++-
 lib/tests/test_bits.c                |  30 ++++++++++
 4 files changed, 96 insertions(+), 100 deletions(-)
---
base-commit: 2df0c02dab829dd89360d98a8a1abaa026ef5798
change-id: 20250228-fixed-type-genmasks-8d1a555f34e8

Best regards,
-- 
Vincent Mailhol <mailhol.vincent at wanadoo.fr>