Introduce some fixed width variant of the GENMASK() and the BIT() macros in bits.h. Note that the main goal is not to get the correct type, but rather to enforce more checks at compile time. 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@xxxxxxxxx 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. In this v4, I introduce one big change: split the definition of the asm and non-asm GENMASK(). I think this is controversial. Especially, Yuri commented that he did not want such split. So I initially implemented a first draft in which both the asm and non-asm version would rely on the same helper macro, i.e. adding this: #define __GENMASK_t(t, w, h, l) \ (((t)~_ULL(0) - ((t)1 << (l)) + 1) & \ ((t)~_ULL(0) >> (w - 1 - (h)))) to uapi/bits.h. And then, the different GENMASK()s would look like this: #define __GENMASK(h, l) __GENMASK_t(unsigned long, __BITS_PER_LONG, h, l) and so on. I implemented it, and the final result looks quite ugly. Not only do we need to manually provide the width each time, the biggest concern is that adding this to the uapi is asking for trouble. Who knows how people are going to use this? And once it is in the uapi, there is virtually no way back. 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. For asm, the long and long long variants seems sufficient. And so, after implementing both, the asm and non-asm split seems way more clean and I think this is the best compromise. Let me know what you think :) 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. v3: https://lore.kernel.org/intel-xe/20240208074521.577076-1-lucas.demarchi@xxxxxxxxx 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. v2: https://lore.kernel.org/intel-xe/20240124050205.3646390-1-lucas.demarchi@xxxxxxxxx v1: https://lore.kernel.org/intel-xe/20230509051403.2748545-1-lucas.demarchi@xxxxxxxxx -- 2.43.0 --- Lucas De Marchi (3): bits: introduce fixed-type BIT drm/i915: Convert REG_GENMASK* to fixed-width GENMASK_* test_bits: add tests for fixed-type genmasks Vincent Mailhol (4): bits: fix typo 'unsigned __init128' -> 'unsigned __int128' bits: split the definition of the asm and non-asm GENMASK() test_bits: add tests for __GENMASK() and __GENMASK_ULL() test_bits: add tests for fixed-type BIT Yury Norov (1): bits: introduce fixed-type genmasks drivers/gpu/drm/i915/i915_reg_defs.h | 108 ++++------------------------------- include/linux/bitops.h | 1 - include/linux/bits.h | 65 +++++++++++++++++---- lib/test_bits.c | 47 +++++++++++++++ 4 files changed, 111 insertions(+), 110 deletions(-) --- base-commit: 7eb172143d5508b4da468ed59ee857c6e5e01da6 change-id: 20250228-fixed-type-genmasks-8d1a555f34e8 Best regards, -- Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
