linux-kernel - Re: [PATCH] staging: iio: ad5933: Use div64_ul instead of do

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Message-ID: <Y1zbyJPF+YUY6xIh@kroah.com>
Date:   Sat, 29 Oct 2022 09:52:40 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Deepak R Varma <drv@...lo.com>
Cc:     outreachy@...ts.linux.dev, Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Jonathan Cameron <jic23@...nel.org>, linux-iio@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: iio: ad5933: Use div64_ul instead of do_div

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@...lo.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