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

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Date:   Mon, 14 Feb 2022 11:01:19 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
CC:     Jonathan Cameron <jic23@...nel.org>, Qing Wang <wangqing@...o.com>,
        "Jyoti Bhayana" <jbhayana@...gle.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()

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 =  
> >>
> >>  
> > 
> >   
>