Re: [PATCH] staging: iio: ad5933: Use div64_ul instead of do_div

Greg Kroah-Hartman
2022-10-29T07:51:44Z

On Fri, Oct 28, 2022 at 02:58:49AM +0530, Deepak R Varma wrote:
> do_div() does a 64-by-32 division. Here the divisor is an unsigned long
> which on some platforms is 64 bit wide. So use div64_ul instead of do_div
> to avoid a possible truncation. Issue was identified using the
> coccicheck tool.
>
> Signed-off-by: Deepak R Varma <drv@mailo.com>
> ---
> drivers/staging/iio/impedance-analyzer/ad5933.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/staging/iio/impedance-analyzer/ad5933.c b/drivers/staging/iio/impedance-analyzer/ad5933.c
> index f177b20f0f2d..730bb31a20d8 100644
> --- a/drivers/staging/iio/impedance-analyzer/ad5933.c
> +++ b/drivers/staging/iio/impedance-analyzer/ad5933.c
> @@ -196,7 +196,7 @@ static int ad5933_set_freq(struct ad5933_state *st,
> } dat;
>
> freqreg = (u64)freq * (u64)(1 << 27);
> - do_div(freqreg, st->mclk_hz / 4);
> + freqreg = div64_ul(freqreg, st->mclk_hz / 4);
>
> switch (reg) {
> case AD5933_REG_FREQ_START:
> --
> 2.34.1

No, this isn't ok, please read the mailing list archives for why these
changes are not going to be accepted:
https://lore.kernel.org/r/e2ec77060cc84a33b49d5fd11d7867f6@AcuMS.aculab.com

Please always at least look at the archives of the past few weeks as to
if changes like this are able to be accepted or not.

thanks,

greg k-h