Re: [Intel-gfx] [PATCH] drm/i915/hwmon: Fix a build error used with clang compiler

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Tue, 25 Oct 2022 07:30:49 -0700, Jani Nikula wrote:
>
> On Tue, 25 Oct 2022, Jani Nikula <jani.nikula@linux.intel.com> wrote:
> > On Tue, 25 Oct 2022, Gwan-gyeong Mun <gwan-gyeong.mun@intel.com> wrote:
> >> If a non-constant variable is used as the first argument of the FIELD_PREP
> >> macro, a build error occurs when using the clang compiler.
> >>
> >> Fix the following build error used with clang compiler:
> >>
> >> 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]
> >>         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@intel.com>
> >> Cc: Anshuman Gupta <anshuman.gupta@intel.com>
> >> Cc: Andi Shyti <andi.shyti@linux.intel.com>
> >> Signed-off-by: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
> >> ---
> >>  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);
> >
> > Please just switch to REG_FIELD_PREP() and it should be fine.
>
> Actually, probably not, but please switch to it anyway. ;)

This is what happens with REG_FIELD_PREP(), that is why we went ahead with
FIELD_PREP(). So REG_FIELD_PREP is not an option.

  CC [M]  drivers/gpu/drm/i915/i915_hwmon.o
In file included from ./include/linux/bits.h:22,
                 from ./include/linux/bitops.h:6,
                 from ./include/linux/hwmon.h:15,
                 from drivers/gpu/drm/i915/i915_hwmon.c:6:
drivers/gpu/drm/i915/i915_hwmon.c: In function ‘hwm_field_scale_and_write’:
./include/linux/build_bug.h:16:51: error: negative width in bit-field ‘<anonymous>’
   16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
      |                                                   ^
./drivers/gpu/drm/i915/i915_reg_defs.h:72:16: note: in expansion of macro ‘BUILD_BUG_ON_ZERO’
   72 |                BUILD_BUG_ON_ZERO(!__is_constexpr(__mask)) +             \
      |                ^~~~~~~~~~~~~~~~~
drivers/gpu/drm/i915/i915_hwmon.c:115:23: note: in expansion of macro ‘REG_FIELD_PREP’
  115 |         bits_to_set = REG_FIELD_PREP(field_msk, nval);
      |                       ^~~~~~~~~~~~~~
./include/linux/build_bug.h:16:51: error: bit-field ‘<anonymous>’ width not an integer constant
   16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
      |                                                   ^
./drivers/gpu/drm/i915/i915_reg_defs.h:73:16: note: in expansion of macro ‘BUILD_BUG_ON_ZERO’
   73 |                BUILD_BUG_ON_ZERO((__mask) == 0 || (__mask) > U32_MAX) +         \
      |                ^~~~~~~~~~~~~~~~~
drivers/gpu/drm/i915/i915_hwmon.c:115:23: note: in expansion of macro ‘REG_FIELD_PREP’
  115 |         bits_to_set = REG_FIELD_PREP(field_msk, nval);
      |                       ^~~~~~~~~~~~~~
./include/linux/build_bug.h:16:51: error: bit-field ‘<anonymous>’ width not an integer constant
   16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
      |                                                   ^
./drivers/gpu/drm/i915/i915_reg_defs.h:74:16: note: in expansion of macro ‘BUILD_BUG_ON_ZERO’
   74 |                BUILD_BUG_ON_ZERO(!IS_POWER_OF_2((__mask) + (1ULL << __bf_shf(__mask)))) + \
      |                ^~~~~~~~~~~~~~~~~
drivers/gpu/drm/i915/i915_hwmon.c:115:23: note: in expansion of macro ‘REG_FIELD_PREP’
  115 |         bits_to_set = REG_FIELD_PREP(field_msk, nval);
      |                       ^~~~~~~~~~~~~~
make[1]: *** [scripts/Makefile.build:250: drivers/gpu/drm/i915/i915_hwmon.o] Error 1
make: *** [Makefile:1992: drivers/gpu/drm/i915] Error 2