No rush, please allow your reviewers a week or two before submitting a new iteration unless you want to disregard the previous version for some reason, of course. This will not get into the upcoming merge window, anyways. So, what should I do? Go through the v5 and all discussions in there, or just jump on this? On Sat, Mar 08, 2025 at 01:48:47AM +0900, Vincent Mailhol via B4 Relay wrote: > 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 v4 and onward, I introduce one big change: split the definition of > the asm and non-asm GENMASK(). I think this is controversial. > Especially, Yury 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_TYPE(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_TYPE(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. > > Adding to this, that macro can not even be generalized to u128 > integers, whereas after the split, it is. > > 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 :) > > 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: 4/2 up/down: 5/-4 (1) > Function old new delta > intel_psr_invalidate 666 668 +2 > mst_stream_compute_config 1652 1653 +1 > intel_psr_flush 977 978 +1 > intel_dp_compute_link_config 1327 1328 +1 > cfg80211_inform_bss_data 5109 5108 -1 > intel_drrs_activate 379 376 -3 > Total: Before=22723481, After=22723482, chg +0.00% > > (done with GCC 12.4.1 on an x86_64 defconfig) > > -- > 2.43.0 > > --- > 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@xxxxxxxxxx > > 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@xxxxxxxxxx > > - 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@xxxxxxxxxx > > 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@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. > > - Link to v2: https://lore.kernel.org/intel-xe/20240124050205.3646390-1-lucas.demarchi@xxxxxxxxx > > Link to v1: https://lore.kernel.org/intel-xe/20230509051403.2748545-1-lucas.demarchi@xxxxxxxxx > > --- > 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: split the definition of the asm and non-asm GENMASK() > test_bits: add tests for __GENMASK() and __GENMASK_ULL() > test_bits: add tests for BIT_U*() > > 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 | 91 ++++++++++++++++++++--------- > lib/test_bits.c | 49 ++++++++++++++++ > 4 files changed, 124 insertions(+), 125 deletions(-) > --- > base-commit: 0312e94abe484b9ee58c32d2f8ba177e04955b35 > change-id: 20250228-fixed-type-genmasks-8d1a555f34e8 > > Best regards, > -- > Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> >
