linux-kernel - Re: [PATCH] iio: use div64_u64() instead of do

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Message-ID: <CA+=V6c31+BvssWX-eG=LdeC8o4mE7e1whnT74jbQWRY2w5Zbqg@mail.gmail.com>
Date:   Mon, 14 Feb 2022 09:42:33 -0800
From:   Jyoti Bhayana <jbhayana@...gle.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Jonathan Cameron <jic23@...nel.org>,
        Qing Wang <wangqing@...o.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: use div64_u64() instead of do_div()

yes, this is wrong. Also, the logic would be broken as the two apis
do_div() and div64_u64 return values are completely different.
Thanks,
Jyoti


On Mon, Feb 14, 2022 at 3:01 AM Jonathan Cameron
<Jonathan.Cameron@...wei.com> wrote:
>
> On Sun, 13 Feb 2022 19:54:01 +0100
> Christophe JAILLET <christophe.jaillet@...adoo.fr> wrote:
>
> > Le 13/02/2022 à 19:50, Christophe JAILLET a écrit :
> > > Le 13/02/2022 à 18:59, Jonathan Cameron a écrit :
> > >> On Wed,  9 Feb 2022 00:37:53 -0800
> > >> Qing Wang <wangqing-DGpbCiVdSXo@...lic.gmane.org> wrote:
> > >>
> > >>> From: Wang Qing <wangqing-DGpbCiVdSXo@...lic.gmane.org>
> > >>>
> > >>> do_div() does a 64-by-32 division.
> > >>> When the divisor is u64, do_div() truncates it to 32 bits, this means it
> > >>> can test non-zero and be truncated to zero for division.
> > >>>
> > >>> fix do_div.cocci warning:
> > >>> do_div() does a 64-by-32 division, please consider using div64_u64
> > >>> instead.
> > >>>
> > >>> Signed-off-by: Wang Qing <wangqing-DGpbCiVdSXo@...lic.gmane.org>
> > >> These look correct to me.  Jyoti, please could give these a sanity check?
> > >>
> > >
> > > This is wrong.
> > >
> > > See [1].
> > >
> > > CJ
> > >
> > > [1]:
> > > https://lore.kernel.org/linux-kernel/20211117112559.jix3hmx7uwqmuryg-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org/
> >
> > Broken link, sorry:
> >
> > [1]
> > https://lore.kernel.org/linux-kernel/20211117112559.jix3hmx7uwqmuryg@pengutronix.de/
> >
> oops.  Thanks for the heads up. I'd forgotten the slightly odd convention
> around do_div
>
> Jonathan
>
>
> > >
> > >
> > >> Thanks,
> > >>
> > >> Jonathan
> > >>
> > >>> ---
> > >>>   drivers/iio/common/scmi_sensors/scmi_iio.c | 10 +++++-----
> > >>>   1 file changed, 5 insertions(+), 5 deletions(-)
> > >>>
> > >>> diff --git a/drivers/iio/common/scmi_sensors/scmi_iio.c
> > >>> b/drivers/iio/common/scmi_sensors/scmi_iio.c
> > >>> index d538bf3..d6df5da
> > >>> --- a/drivers/iio/common/scmi_sensors/scmi_iio.c
> > >>> +++ b/drivers/iio/common/scmi_sensors/scmi_iio.c
> > >>> @@ -160,7 +160,7 @@ static int scmi_iio_set_odr_val(struct iio_dev
> > >>> *iio_dev, int val, int val2)
> > >>>       mult = scnprintf(buf, sizeof(buf), "%llu", sf) - 1;
> > >>>       sec = int_pow(10, mult) * UHZ_PER_HZ;
> > >>> -    do_div(sec, uHz);
> > >>> +    div64_u64(sec, uHz);
> > >>>       if (sec == 0) {
> > >>>           dev_err(&iio_dev->dev,
> > >>>               "Trying to set invalid sensor update value for sensor %s",
> > >>> @@ -237,10 +237,10 @@ static void convert_ns_to_freq(u64 interval_ns,
> > >>> u64 *hz, u64 *uhz)
> > >>>       u64 rem, freq;
> > >>>       freq = NSEC_PER_SEC;
> > >>> -    rem = do_div(freq, interval_ns);
> > >>> +    rem = div64_u64(freq, interval_ns);
> > >>>       *hz = freq;
> > >>>       *uhz = rem * 1000000UL;
> > >>> -    do_div(*uhz, interval_ns);
> > >>> +    div64_u64(*uhz, interval_ns);
> > >>>   }
> > >>>   static int scmi_iio_get_odr_val(struct iio_dev *iio_dev, int *val,
> > >>> int *val2)
> > >>> @@ -266,7 +266,7 @@ static int scmi_iio_get_odr_val(struct iio_dev
> > >>> *iio_dev, int *val, int *val2)
> > >>>       mult = SCMI_SENS_CFG_GET_UPDATE_EXP(sensor_config);
> > >>>       if (mult < 0) {
> > >>>           sensor_interval_mult = int_pow(10, abs(mult));
> > >>> -        do_div(sensor_update_interval, sensor_interval_mult);
> > >>> +        div64_u64(sensor_update_interval, sensor_interval_mult);
> > >>>       } else {
> > >>>           sensor_interval_mult = int_pow(10, mult);
> > >>>           sensor_update_interval =
> > >>> @@ -500,7 +500,7 @@ static u64 scmi_iio_convert_interval_to_ns(u32 val)
> > >>>       mult = SCMI_SENS_INTVL_GET_EXP(val);
> > >>>       if (mult < 0) {
> > >>>           sensor_interval_mult = int_pow(10, abs(mult));
> > >>> -        do_div(sensor_update_interval, sensor_interval_mult);
> > >>> +        div64_u64(sensor_update_interval, sensor_interval_mult);
> > >>>       } else {
> > >>>           sensor_interval_mult = int_pow(10, mult);
> > >>>           sensor_update_interval =
> > >>
> > >>
> > >
> > >
> >
>