[PATCH] iio: hid-sensors: fix fractional part for unit exponents -7 and -8

[PATCH] iio: hid-sensors: fix fractional part for unit exponents -7 and -8

[Srinivas Pandruvada]

split_micro_fraction() scales the remainder to micro units by
multiplying it by 10^(6 - exp). The unit exponent of a HID field goes
down to -8, so exp can be 7 or 8 here. Then the argument of int_pow()
is negative, which the unsigned parameter turns into a huge power of
ten: 0 modulo 2^64. As a result, the fractional part of a value read
from the hysteresis attributes is always reported as 0.

Divide by 10^(exp - 6) in these two cases. This matches the reverse
conversion in convert_to_vtf_format().

Fixes: 73c6768b710a ("iio: hid-sensors: Common attribute and trigger")
Cc: stable@vger.kernel.org
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
---
 drivers/iio/common/hid-sensors/hid-sensor-attributes.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/common/hid-sensors/hid-sensor-attributes.c b/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
index 9e7c26e37880..0e6ea5373434 100644
--- a/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
+++ b/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
@@ -98,7 +98,10 @@ static void split_micro_fraction(unsigned int no, int exp, int *val1, int *val2)
 	int divisor = int_pow(10, exp);
 
 	*val1 = no / divisor;
-	*val2 = no % divisor * int_pow(10, 6 - exp);
+	if (exp > 6)
+		*val2 = no % divisor / int_pow(10, exp - 6);
+	else
+		*val2 = no % divisor * int_pow(10, 6 - exp);
 }
 
 /*
-- 
2.56.0

Re: [PATCH] iio: hid-sensors: fix fractional part for unit exponents -7 and -8

[Andy Shevchenko]

On Mon, Nov 02, 2026 at 02:23:08PM -0800, Srinivas Pandruvada wrote:
> split_micro_fraction() scales the remainder to micro units by
> multiplying it by 10^(6 - exp). The unit exponent of a HID field goes
> down to -8, so exp can be 7 or 8 here. Then the argument of int_pow()
> is negative, which the unsigned parameter turns into a huge power of
> ten: 0 modulo 2^64. As a result, the fractional part of a value read
> from the hysteresis attributes is always reported as 0.
> 
> Divide by 10^(exp - 6) in these two cases. This matches the reverse
> conversion in convert_to_vtf_format().

...

>  	*val1 = no / divisor;
> -	*val2 = no % divisor * int_pow(10, 6 - exp);
> +	if (exp > 6)
> +		*val2 = no % divisor / int_pow(10, exp - 6);
> +	else
> +		*val2 = no % divisor * int_pow(10, 6 - exp);

Please, make no % divisor to be in a temporary variable. It may lead to

	foo = var / div;
	bar = var % div;

compiled to the single assembly instruction (on x86, for example).

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] iio: hid-sensors: fix fractional part for unit exponents -7 and -8

[kernel test robot]

Hi Srinivas,

kernel test robot noticed the following build errors:

[auto build test ERROR on jic23-iio/togreg]
[also build test ERROR on linus/master v7.3 next-20261030]
[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#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Srinivas-Pandruvada/iio-hid-sensors-fix-fractional-part-for-unit-exponents-7-and-8/20261102-142308
base:   https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git togreg
patch link:    https://lore.kernel.org/r/20261102222309.439895-1-srinivas.pandruvada%40linux.intel.com
patch subject: [PATCH] iio: hid-sensors: fix fractional part for unit exponents -7 and -8
config: parisc-randconfig-1000-20261104 (https://download.01.org/0day-ci/archive/20261104/202611040803.1mUBmX0y-lkp@intel.com/config)
compiler: hppa-linux-gcc (GCC) 8.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20261104/202611040803.1mUBmX0y-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202611040803.1mUBmX0y-lkp@intel.com/

All errors (new ones prefixed by >>, old ones prefixed by <<):

>> ERROR: modpost: drivers/iio/common/hid-sensors/hid-sensor-iio-common.ko: symbol '__udivdi3' undefined!

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] iio: hid-sensors: fix fractional part for unit exponents -7 and -8

[kernel test robot]

Hi Srinivas,

kernel test robot noticed the following build errors:

[auto build test ERROR on jic23-iio/togreg]
[also build test ERROR on linus/master v7.3 next-20261030]
[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#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Srinivas-Pandruvada/iio-hid-sensors-fix-fractional-part-for-unit-exponents-7-and-8/20261102-142308
base:   https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git togreg
patch link:    https://lore.kernel.org/r/20261102222309.439895-1-srinivas.pandruvada%40linux.intel.com
patch subject: [PATCH] iio: hid-sensors: fix fractional part for unit exponents -7 and -8
config: i386-randconfig-1001-20261103 (https://download.01.org/0day-ci/archive/20261104/202611040826.T95bI1SU-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.4.0-5) 12.4.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20261104/202611040826.T95bI1SU-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202611040826.T95bI1SU-lkp@intel.com/

All errors (new ones prefixed by >>):

   ld: drivers/iio/common/hid-sensors/hid-sensor-attributes.o: in function `split_micro_fraction':
>> drivers/iio/common/hid-sensors/hid-sensor-attributes.c:102:(.text+0x573): undefined reference to `__udivdi3'


vim +102 drivers/iio/common/hid-sensors/hid-sensor-attributes.c

    95	
    96	static void split_micro_fraction(unsigned int no, int exp, int *val1, int *val2)
    97	{
    98		int divisor = int_pow(10, exp);
    99	
   100		*val1 = no / divisor;
   101		if (exp > 6)
 > 102			*val2 = no % divisor / int_pow(10, exp - 6);
   103		else
   104			*val2 = no % divisor * int_pow(10, 6 - exp);
   105	}
   106	

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki