Re: [PATCH v8 09/14] iio: afe: rescale: fix accuracy for small fractional scales

[kernel test robot <lkp@xxxxxxxxx>]

Hi Liam,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on 6cbb3aa0f9d5d23221df787cf36f74d3866fdb78]

url:    https://github.com/0day-ci/linux/commits/Liam-Beguin/iio-afe-add-temperature-rescaling-support/20210821-032112
base:   6cbb3aa0f9d5d23221df787cf36f74d3866fdb78
config: i386-randconfig-r026-20210821 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce (this is a W=1 build):
        # https://github.com/0day-ci/linux/commit/e5c2e1505fa3f8cf9fe6d3a21f3a5c585efc6dce
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Liam-Beguin/iio-afe-add-temperature-rescaling-support/20210821-032112
        git checkout e5c2e1505fa3f8cf9fe6d3a21f3a5c585efc6dce
        # save the attached .config to linux build tree
        mkdir build_dir
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>

All errors (new ones prefixed by >>):

   ld: drivers/iio/afe/iio-rescale.o: in function `rescale_process_scale':
>> drivers/iio/afe/iio-rescale.c:56: undefined reference to `__divdi3'


vim +56 drivers/iio/afe/iio-rescale.c

    20	
    21	int rescale_process_scale(struct rescale *rescale, int scale_type,
    22				  int *val, int *val2)
    23	{
    24		s64 tmp;
    25		s32 rem, rem2;
    26		u32 mult;
    27		u32 neg;
    28	
    29		switch (scale_type) {
    30		case IIO_VAL_INT:
    31			*val *= rescale->numerator;
    32			if (rescale->denominator == 1)
    33				return scale_type;
    34			*val2 = rescale->denominator;
    35			return IIO_VAL_FRACTIONAL;
    36		case IIO_VAL_FRACTIONAL:
    37		case IIO_VAL_FRACTIONAL_LOG2:
    38			tmp = (s64)*val * 1000000000LL;
    39			tmp = div_s64(tmp, rescale->denominator);
    40			tmp *= rescale->numerator;
    41	
    42			tmp = div_s64_rem(tmp, 1000000000LL, &rem);
    43			*val = tmp;
    44	
    45			/*
    46			 * For small values, the approximation can be costly,
    47			 * change scale type to maintain accuracy.
    48			 *
    49			 * 100 vs. 10000000 NANO caps the error to about 100 ppm.
    50			 */
    51			if (scale_type == IIO_VAL_FRACTIONAL)
    52				tmp = *val2;
    53			else
    54				tmp = 1 << *val2;
    55	
  > 56			 if (abs(rem) > 10000000 && abs(*val / tmp) < 100) {
    57				 *val = div_s64_rem(*val, tmp, &rem2);
    58	
    59				 *val2 = div_s64(rem, tmp);
    60				 if (rem2)
    61					 *val2 += div_s64(rem2 * 1000000000LL, tmp);
    62	
    63				 return IIO_VAL_INT_PLUS_NANO;
    64			 }
    65	
    66			return scale_type;
    67		case IIO_VAL_INT_PLUS_NANO:
    68		case IIO_VAL_INT_PLUS_MICRO:
    69			if (scale_type == IIO_VAL_INT_PLUS_NANO)
    70				mult = 1000000000LL;
    71			else
    72				mult = 1000000LL;
    73			/*
    74			 * For IIO_VAL_INT_PLUS_{MICRO,NANO} scale types if *val OR
    75			 * *val2 is negative the schan scale is negative
    76			 */
    77			neg = *val < 0 || *val2 < 0;
    78	
    79			tmp = (s64)abs(*val) * abs(rescale->numerator);
    80			*val = div_s64_rem(tmp, abs(rescale->denominator), &rem);
    81	
    82			tmp = (s64)rem * mult + (s64)abs(*val2) * abs(rescale->numerator);
    83			tmp = div_s64(tmp, abs(rescale->denominator));
    84	
    85			*val += div_s64_rem(tmp, mult, val2);
    86	
    87			/*
    88			 * If only one of the rescaler elements or the schan scale is
    89			 * negative, the combined scale is negative.
    90			 */
    91			if (neg ^ ((rescale->numerator < 0) ^ (rescale->denominator < 0))) {
    92				if (*val)
    93					*val = -*val;
    94				else
    95					*val2 = -*val2;
    96			}
    97	
    98			return scale_type;
    99		default:
   100			return -EOPNOTSUPP;
   101		}
   102	}
   103	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@xxxxxxxxxxxx

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