Re: [PATCH v2] iio: common: scmi_sensors: fix truncating 64-bit divisions

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Tue, Oct 06, 2026 at 10:22:41AM +0530, Arnav Kapoor wrote:
> do_div() divides a 64-bit dividend by a 32-bit divisor: the divisor is
> stored in a uint32_t on all architectures. The driver passes 64-bit
> divisors to it in several places, so they are silently truncated:
> 
> - scmi_iio_set_odr_val() divides by uHz, which exceeds 32 bits for
>   sampling frequencies above ~4294 Hz.
> - convert_ns_to_freq() divides by interval_ns, which exceeds 32 bits
>   for update intervals of ~4.29 s and above. If its low 32 bits happen
>   to be zero, this is a division by zero.
> - scmi_iio_get_odr_val(), scmi_iio_convert_interval_to_ns(),
>   scmi_iio_sensor_update_cb() and scmi_iio_get_raw_available() divide
>   by int_pow(10, n), which returns u64 and exceeds 32 bits for n >= 10.
>   The SCMI exponent fields allow values down to -16.
> 
> Truncation results in wrong sampling frequency, timestamp and
> raw_available values being reported to userspace.
> 
> Use div64_u64() and div64_u64_rem(), which take a 64-bit divisor.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>

-- 
With Best Regards,
Andy Shevchenko