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

[Семён Марьясин]

Tested-by: Semyon Maryasin <simeon@xxxxxxxxxxxxx>

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?

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@xxxxxxxxxxxxxxx>:
>
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
> ---
> 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
>
>


-- 
С уважением,
Семён Марьясин