Hi Andreas,

I love your patch! Perhaps something to improve:

[auto build test WARNING on iio/togreg]
[also build test WARNING on robh/for-next linus/master v5.14-rc3 next-20210727]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Andreas-Klinger/iio-chemical-Add-support-for-sgp40-gas-sensor/20210728-003718
base:   https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git togreg
config: i386-allyesconfig (attached as .config)
compiler: gcc-10 (Ubuntu 10.3.0-1ubuntu1~20.04) 10.3.0
reproduce (this is a W=1 build):
        # https://github.com/0day-ci/linux/commit/6e2c78f8b661002ac418f2782ddc79352b6f04a3
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Andreas-Klinger/iio-chemical-Add-support-for-sgp40-gas-sensor/20210728-003718
        git checkout 6e2c78f8b661002ac418f2782ddc79352b6f04a3
        # save the attached .config to linux build tree
        make W=1 ARCH=i386 

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

All warnings (new ones prefixed by >>):

>> drivers/iio/chemical/sgp40.c:67:5: warning: no previous prototype for 'sqp40_exp100' [-Wmissing-prototypes]
      67 | int sqp40_exp100(int n)
         |     ^~~~~~~~~~~~


vim +/sqp40_exp100 +67 drivers/iio/chemical/sgp40.c

    60	
    61	/*
    62	 * calculate e^x where n is the exponent multiplied with 100
    63	 *
    64	 * use taylor approximation which is accurate enough for the purpose of
    65	 * coming out with just 500 index points.
    66	 */
  > 67	int sqp40_exp100(int n)
    68	{
    69		int x, xn, y, z;
    70		int s = 1;
    71	
    72		if (n < 0) {
    73			s = -1;
    74			n *= -1;
    75		}
    76	
    77		x = n;
    78	
    79		y = 100 + x;
    80		xn = x * x;
    81		y += xn / 2 / 100;
    82		xn = x * x * x;
    83		y += xn / 6 / 10000;
    84		xn = x * x * x * x;
    85		y += xn / 24 / 1000000;
    86	
    87		if (s == -1)
    88			z = 10000 / y;
    89		else
    90			z = y;
    91	
    92		return z;
    93	}
    94	

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