Re: [PATCH] iio: use div64_u64() instead of do_div()

[Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>]

Le 13/02/2022 à 18:59, Jonathan Cameron a écrit :
> On Wed,  9 Feb 2022 00:37:53 -0800
> Qing Wang <wangqing@xxxxxxxx> wrote:
>
> > From: Wang Qing <wangqing@xxxxxxxx>
> >
> > 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@xxxxxxxx>
> 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@xxxxxxxxxxxxxx/

> 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 =