Start of lore thread for context: https://lore.kernel.org/intel-gfx/20221024210953.1572998-1-gwan-gyeong.mun@xxxxxxxxx/ On Tue, Oct 25, 2022 at 2:25 AM Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx> wrote: > > Hi Ashutosh, > > > > drivers/gpu/drm/i915/i915_hwmon.c:115:16: error: result of comparison of constant 18446744073709551615 with expression of type 'typeof (_Generic((field_msk), char: (unsigned char)0, unsigned char: (unsigned char)0, signed char: (unsigned char)0, unsigned short: (unsigned short)0, short: (unsigned short)0, unsigned int: (unsigned int)0, int: (unsigned int)0, unsigned long: (unsigned long)0, long: (unsigned long)0, unsigned long long: (unsigned long long)0, long long: (unsigned long long)0, default: (field_msk)))' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare] > > > > What is 18446744073709551615? You may want to limit the length of this line > > or checkpatch doesn't complain? > > yeah! I am not a clang user, and this must be some ugly error > output. I don't think it makes sense to break it, though. > > > > bits_to_set = FIELD_PREP(field_msk, nval); > > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > ./include/linux/bitfield.h:114:3: note: expanded from macro 'FIELD_PREP' > > > __BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_PREP: "); \ > > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > ./include/linux/bitfield.h:71:53: note: expanded from macro '__BF_FIELD_CHECK' > > > BUILD_BUG_ON_MSG(__bf_cast_unsigned(_mask, _mask) > \ > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~ > > > ./include/linux/build_bug.h:39:58: note: expanded from macro 'BUILD_BUG_ON_MSG' > > > ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~ > > > ./include/linux/compiler_types.h:357:22: note: expanded from macro 'compiletime_assert' > > > _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) > > > ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > ./include/linux/compiler_types.h:345:23: note: expanded from macro '_compiletime_assert' > > > __compiletime_assert(condition, msg, prefix, suffix) > > > ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > ./include/linux/compiler_types.h:337:9: note: expanded from macro '__compiletime_assert' > > > if (!(condition)) \ > > > > > > Fixes: 99f55efb7911 ("drm/i915/hwmon: Power PL1 limit and TDP setting") > > > Cc: Ashutosh Dixit <ashutosh.dixit@xxxxxxxxx> > > > Cc: Anshuman Gupta <anshuman.gupta@xxxxxxxxx> > > > Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx> > > > Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@xxxxxxxxx> > > > --- > > > drivers/gpu/drm/i915/i915_hwmon.c | 12 +++--------- > > > 1 file changed, 3 insertions(+), 9 deletions(-) > > > > > > diff --git a/drivers/gpu/drm/i915/i915_hwmon.c b/drivers/gpu/drm/i915/i915_hwmon.c > > > index 9e9781493025..782a621b1928 100644 > > > --- a/drivers/gpu/drm/i915/i915_hwmon.c > > > +++ b/drivers/gpu/drm/i915/i915_hwmon.c > > > @@ -101,21 +101,16 @@ hwm_field_read_and_scale(struct hwm_drvdata *ddat, i915_reg_t rgadr, > > > > > > static void > > > hwm_field_scale_and_write(struct hwm_drvdata *ddat, i915_reg_t rgadr, > > > - u32 field_msk, int nshift, > > > - unsigned int scale_factor, long lval) > > > + int nshift, unsigned int scale_factor, long lval) > > > { > > > u32 nval; > > > - u32 bits_to_clear; > > > - u32 bits_to_set; > > > > > > /* Computation in 64-bits to avoid overflow. Round to nearest. */ > > > nval = DIV_ROUND_CLOSEST_ULL((u64)lval << nshift, scale_factor); > > > > > > - bits_to_clear = field_msk; > > > - bits_to_set = FIELD_PREP(field_msk, nval); > > > - > > > hwm_locked_with_pm_intel_uncore_rmw(ddat, rgadr, > > > - bits_to_clear, bits_to_set); > > > + PKG_PWR_LIM_1, > > > + FIELD_PREP(PKG_PWR_LIM_1, nval)); > > > > I don't want to give up so easily. We might have future uses for the > > function where we want field_msk to be passed into the function (rather > > than set inside the function as in this patch). > > > > Do we understand what clang is complaining about? And why this compiles > > with gcc? > > Because we are not compiling the builtin functions with gcc but > gcc has support for them. The FIELD_PREP checks if the first > parameter is a constant: > > BUILD_BUG_ON_MSG(!__builtin_constant_p(_mask), > > where _mask was our field_mask, but we ignore it. Apparently > clang doesn't. So we've been in this code before. I'm having vague memories of commit 444da3f52407 ("bitfield.h: don't compile-time validate _val in FIELD_FIT") But looking at the first __builtin_constant_p check in __BF_FIELD_CHECK, I'm curious if that might need to be __is_constexpr rather than __builtin_constant_p; a change like commit 4d45bc82df66 ("coresight: etm4x: avoid build failure with unrolled loops") __builtin_constant_p is evaluated after most optimizations have run; __is_constexpr must be evaluated by compiler front ends during semantic analysis. But reading through the full lore thread, it sounds like Jani has another suggestion to try instead. https://lore.kernel.org/intel-gfx/87eduwdllr.fsf@xxxxxxxxx/ Please re-cc us and our list if that doesn't work out. > > If we want to stick to gcc only, then I still think the patch is > correct for two reasons: > > 1. it's cleaner > 2. we would get on with the job and if one day we will decide > to suppport builtin functions in gcc as well, we will sleep > peacefully :) > > > Copying llvm@xxxxxxxxxxxxxxx too. > > maybe llvm folks have a better opinion. > > Thanks, > Andi > > > Thanks. > > -- > > Ashutosh > > > > > > > } > > > > > > /* > > > @@ -406,7 +401,6 @@ hwm_power_write(struct hwm_drvdata *ddat, u32 attr, int chan, long val) > > > case hwmon_power_max: > > > hwm_field_scale_and_write(ddat, > > > hwmon->rg.pkg_rapl_limit, > > > - PKG_PWR_LIM_1, > > > hwmon->scl_shift_power, > > > SF_POWER, val); > > > return 0; > > > -- > > > 2.37.1 > > > > -- Thanks, ~Nick Desaulniers
