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

[Jonathan Cameron]

On Thu, 15 Oct 2026 22:54:23 +0300
Andy Shevchenko <andriy.shevchenko@xxxxxxxxx> wrote:

> 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@xxxxxxxxx>
> 
Hmm. This came up before but they never came back with the code
fixes asked for:
https://lore.kernel.org/all/1644395873-3937-1-git-send-email-wangqing@xxxxxxxx/

Anyhow, this looks good and I haven't heard from Jyoti for a few years
so will pick it up without waiting for a tag (most welcome though if Jyoti
is still active!)

Applied to the fixes-togreg branch of iio.git