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Date:   Mon, 14 Feb 2022 11:01:19 +0000
From:   Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To:     Christophe JAILLET <christophe.jaillet@wanadoo.fr>
CC:     Jonathan Cameron <jic23@kernel.org>, Qing Wang <wangqing@vivo.com>,
        "Jyoti Bhayana" <jbhayana@google.com>,
        Lars-Peter Clausen <lars@metafoo.de>,
        <linux-iio@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] iio: use div64_u64() instead of do_div()
Message-ID: <20220214110119.00006347@Huawei.com>
In-Reply-To: <29e74800-1c3f-e043-97e6-d83f7a53fafb@wanadoo.fr>
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        <9e5ed543-cd45-85db-50b5-52c2afd54c55@wanadoo.fr>
        <29e74800-1c3f-e043-97e6-d83f7a53fafb@wanadoo.fr>
Organization: Huawei Technologies Research and Development (UK) Ltd.
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On Sun, 13 Feb 2022 19:54:01 +0100
Christophe JAILLET <christophe.jaillet@wanadoo.fr> wrote:

> Le 13/02/2022 ? 19:50, Christophe JAILLET a ?crit?:
> > Le 13/02/2022 ? 18:59, Jonathan Cameron a ?crit?:  
> >> On Wed,? 9 Feb 2022 00:37:53 -0800
> >> Qing Wang <wangqing-DGpbCiVdSXo@public.gmane.org> wrote:
> >>  
> >>> From: Wang Qing <wangqing-DGpbCiVdSXo@public.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@public.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 =  
> >>
> >>  
> > 
> >   
>