Re: [PATCH v2] iio: hid-sensors: fix fractional part for unit exponents -7 and -8

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 05 Nov 2026 15:56:26 -0800
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> wrote:

> On Thu, 2026-11-05 at 22:26 +0300, Семён Марьясин wrote:
> > Tested-by: Semyon Maryasin <simeon@maryasin.name>
> > 
> > Here is what I observe with this patch:
> > 1. Enable sensor and run xxd /dev/HID-SENSOR-2000e1.3.auto
> > 2. In the second terminal, do rmmod intel_ishtp_hid
> > 3. Observed result: xxd stops with "xxd: No such device"
> > 4. At the same time, in kernel logs I see the following:
> > 
> > ноя 05 22:19:16 dook kernel: hid-sensor-hub 001F:8087:0AC2.0005:
> > timeout waiting for response from ISHTP device
> > ноя 05 22:19:19 dook kernel: hid-sensor-hub 001F:8087:0AC2.0005:
> > timeout waiting for response from ISHTP device
> > ноя 05 22:19:22 dook kernel: hid-sensor-hub 001F:8087:0AC2.0006:
> > timeout waiting for response from ISHTP device
> > ноя 05 22:19:25 dook kernel: hid-sensor-hub 001F:8087:0AC2.0006:
> > timeout waiting for response from ISHTP device
> > 
> > No system crash, so I suppose this is okay?
> >   
> That is fine.
Applied to the fixes-togreg branch of iio.git.

Thanks,

Jonathan

> 
> Thanks,
> Srinivas
> 
> 
> > After subsequent modprobe the sensor initializes and works properly.
> > No kernel crash with this patch.
> > 
> > ср, 4 нояб. 2026 г. в 19:53, Srinivas Pandruvada
> > <srinivas.pandruvada@linux.intel.com>:  
> > > 
> > > 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>
> > > ---
> > > v2:
> > > - Fix __udivdi3 link error on 32-bit by using a 32-bit divisor
> > > - Address Andy's comment:
> > > Keep no % divisor in a temporary variable next to no / divisor
> > > 
> > >  drivers/iio/common/hid-sensors/hid-sensor-attributes.c | 7 ++++++-
> > >  1 file changed, 6 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..d44091faf122 100644
> > > --- a/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
> > > +++ b/drivers/iio/common/hid-sensors/hid-sensor-attributes.c
> > > @@ -96,9 +96,14 @@ static void simple_div(int dividend, int
> > > divisor, int *whole, int *micro_frac)
> > >  static void split_micro_fraction(unsigned int no, int exp, int
> > > *val1, int *val2)
> > >  {
> > >         int divisor = int_pow(10, exp);
> > > +       unsigned int rem;
> > > 
> > >         *val1 = no / divisor;
> > > -       *val2 = no % divisor * int_pow(10, 6 - exp);
> > > +       rem = no % divisor;
> > > +       if (exp > 6)
> > > +               *val2 = rem / (unsigned int)int_pow(10, exp - 6);
> > > +       else
> > > +               *val2 = rem * int_pow(10, 6 - exp);
> > >  }
> > > 
> > >  /*
> > > --
> > > 2.56.0
> > > 
> > >   
> >