Re: [PATCH 14/15] iio: scmi: use 64-bit divisions for rates and intervals

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 27 Oct 2026 17:19:18 +0100
Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote:

> From: Josef Bacik <josef@toxicpanda.com>
> 
> do_div() only uses the low 32 bits of its divisor.  Two divisors in this
> driver need more:
> 
> - scmi_iio_set_odr_val() divides by the requested sampling frequency in
>   micro-Hertz, which exceeds 32 bits from 4295 Hz on.  The update interval
>   sent to the firmware is then computed from the wrong frequency.
> - convert_ns_to_freq() divides by the update interval in nanoseconds, which
>   exceeds 32 bits from 4.3 seconds on.  The sampling frequency and the list
>   of available frequencies of a slow sensor are reported wrong.
> 
> Use div64_u64().  A requested frequency of 0, which was a division by zero,
> is refused with -EINVAL like other values that cannot be represented.
> 
> Fixes: f774117c96f9 ("iio/scmi: Adding support for IIO SCMI Based Sensors")
> Cc: stable <stable@kernel.org>
> Cc: Jyoti Bhayana <jbhayana@google.com>
> Cc: David Lechner <dlechner@baylibre.com>
> Cc: "Nuno Sá" <nuno.sa@analog.com>
> Cc: Andy Shevchenko <andy@kernel.org>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

We have some other fixes in this area. They don't completely overlap
though much of the content does match.

https://lore.kernel.org/all/20261006045244.13993-1-kapoorarnav43@gmail.com/

> ---
>  drivers/iio/common/scmi_sensors/scmi_iio.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/iio/common/scmi_sensors/scmi_iio.c b/drivers/iio/common/scmi_sensors/scmi_iio.c
> index 442b40ef27cf..0e51e9c16b90 100644
> --- a/drivers/iio/common/scmi_sensors/scmi_iio.c
> +++ b/drivers/iio/common/scmi_sensors/scmi_iio.c
> @@ -161,8 +161,7 @@ static int scmi_iio_set_odr_val(struct iio_dev *iio_dev, int val, int val2)
>  	do_div(sf,  MICROHZ_PER_HZ);
>  	mult = scnprintf(buf, sizeof(buf), "%llu", sf) - 1;
>  
> -	sec = int_pow(10, mult) * MICROHZ_PER_HZ;
> -	do_div(sec, uHz);
> +	sec = uHz ? div64_u64(int_pow(10, mult) * MICROHZ_PER_HZ, uHz) : 0;
>  	if (sec == 0) {
>  		dev_err(&iio_dev->dev,
>  			"Trying to set invalid sensor update value for sensor %s",
> @@ -237,13 +236,10 @@ static int scmi_iio_read_avail(struct iio_dev *iio_dev,
>  
>  static void convert_ns_to_freq(u64 interval_ns, u64 *hz, u64 *uhz)
>  {
> -	u64 rem, freq;
> +	u64 rem;
>  
> -	freq = NSEC_PER_SEC;
> -	rem = do_div(freq, interval_ns);
> -	*hz = freq;
> -	*uhz = rem * 1000000UL;
> -	do_div(*uhz, interval_ns);
> +	*hz = div64_u64_rem(NSEC_PER_SEC, interval_ns, &rem);
> +	*uhz = div64_u64(rem * 1000000UL, interval_ns);
>  }
>  
>  static int scmi_iio_get_odr_val(struct iio_dev *iio_dev, int *val, int *val2)
>