Re: [PATCH] staging: iio: frequency: ad9832/ad9834: use div64_ul instead of do_div

[Joshua Crofts]

On Tue, 30 Jun 2026 08:53:22 +0530
Mohamad Raizudeen <raizudeen.kerneldev@xxxxxxxxx> wrote:

> Coccinelle warns that do_div() should not be used when the divisor is an unsigned long, because do_div() expects a 32-bit divisor.
> 
> In this case, the 'mclk' divisor is an 'unsigned long', which can be 64-bit on certain architectures. The correct function to use here is div64_ul().
> 
> Because do_div() modifies the dividend in place, while div64_ul() returns the result, the code was updated to directly return the result of div64_ul. This keeps the math exactly the same but fixes the warning and makes the code safer.

Please try to wrap your lines to 72 characters.

> 
> Signed-off-by: Mohamad Raizudeen <raizudeen.kerneldev@xxxxxxxxx>
> ---
>  drivers/staging/iio/frequency/ad9832.c | 3 +--
>  drivers/staging/iio/frequency/ad9834.c | 3 +--
>  2 files changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/staging/iio/frequency/ad9832.c b/drivers/staging/iio/frequency/ad9832.c
> index b87ea1781b27..91df7ee65bfc 100644
> --- a/drivers/staging/iio/frequency/ad9832.c
> +++ b/drivers/staging/iio/frequency/ad9832.c
> @@ -115,8 +115,7 @@ static unsigned long ad9832_calc_freqreg(unsigned long mclk, unsigned long fout)
>  {
>  	unsigned long long freqreg = (u64)fout *
>  				     (u64)((u64)1L << AD9832_FREQ_BITS);
> -	do_div(freqreg, mclk);
> -	return freqreg;
> +	return div64_ul(freqreg, mclk);
>  }

I've actually sent a patch for this previously, however the
discussion ended with the fact that there really isn't a point in
doing this, since mclk will always be a value that can fit
into a 32-bit unsigned type, therefore truncation isn't possible.

See here:
https://lore.kernel.org/all/20260409182755.499a419c@pumpkin/

-- 
Kind regards

CJD