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

[Jani Nikula <jani.nikula@linux.intel.com>]

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.

BR,
Jani.


> -
>  	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));
>  }
>  
>  /*
> @@ -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;

-- 
Jani Nikula, Intel Open Source Graphics Center