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

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Date:   Mon, 31 Oct 2022 15:36:21 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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 Sat, Oct 29, 2022 at 09:52:40AM +0200, Greg Kroah-Hartman wrote:
> 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.

Hello Greg,
My apologies for not looking at the lore mailing archive. I only looked at the
past git commits and found a few similar changes accepted in the past. My bad. I
will always look at the mailing archive as well going forward.

There are other review comments from the experts on similar patches. I
appreciate everyone's time and comment. I will look at those and revert
accordingly.

Thank you,
./drv
>
> thanks,
>
> greg k-h