Re: [PATCH v2] staging: iio: frequency: ad9832/ad9834: add comment explaining do_div usage

[Joshua Crofts]

On Wed, 22 Jul 2026 13:52:27 +0530
Mohamad Raizudeen <raizudeen.kerneldev@xxxxxxxxx> wrote:
> Previous attempts to change do_div() to div64_ul() were rejected because
> mclk will always fit within 32 bits for this hardware, making do_div()
> safe to use.
> 
> However, Coccinelle continues to flag this as a false positive. To
> prevent future developers from submitting unnecessary fixes, add a
> comment explaining why do_div() is intentionally kept.
> 
> Suggested-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>
> Signed-off-by: Mohamad Raizudeen <raizudeen.kerneldev@xxxxxxxxx>
> ---

Please don't send a new version as a reply to the previous version,
as it can break tooling such as b4 for patch review.

As for the comment, I think it's good, however I'm not sure whether
this should be split into two patches, given that this is a small
change. Andy, what do you think?

> diff --git a/drivers/staging/iio/frequency/ad9832.c b/drivers/staging/iio/frequency/ad9832.c
> index 60c33e10c46f..6d046e9121e2 100644
> --- a/drivers/staging/iio/frequency/ad9832.c
> +++ b/drivers/staging/iio/frequency/ad9832.c
> @@ -118,6 +118,13 @@ static unsigned long ad9832_calc_freqreg(unsigned long mclk, unsigned long fout)
>  {
>  	u64 freqreg = (u64)fout << AD9832_FREQ_BITS;
>  
> +       /*
> +	* mclk is an unsigned long, which triggers a Coccinelle false positive
> +	* warning about using do_div() for 64-by-32 division. However, mclk
> +	* for this hardware will always fit within 32 bits, so do_div() is
> +	* safe to use here.
> +	*/
> +

Unnecessary blank line here, you want to couple the comment with the
line that it's describing.

>  	do_div(freqreg, mclk);
>  	return freqreg;
>  }
> diff --git a/drivers/staging/iio/frequency/ad9834.c b/drivers/staging/iio/frequency/ad9834.c
> index 33dfd723923c..8722f3a01cde 100644
> --- a/drivers/staging/iio/frequency/ad9834.c
> +++ b/drivers/staging/iio/frequency/ad9834.c
> @@ -103,6 +103,13 @@ static unsigned int ad9834_calc_freqreg(unsigned long mclk, unsigned long fout)
>  {
>  	unsigned long long freqreg = (u64)fout * (u64)BIT(AD9834_FREQ_BITS);
>  
> +       /*
> +	* mclk is an unsigned long, which triggers a Coccinelle false positive
> +	* warning about using do_div() for 64-by-32 division. However, mclk
> +	* for this hardware will always fit within 32 bits, so do_div() is
> +	* safe to use here.
> +	*/
> +

Ditto.

>  	do_div(freqreg, mclk);
>  	return freqreg;
>  }



-- 
Kind regards,
Joshua Crofts