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

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Date:   Sun, 13 Feb 2022 19:54:01 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Jonathan Cameron <jic23@...nel.org>, Qing Wang <wangqing@...o.com>
Cc:     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()

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/

> 
> 
>> 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 =
>>
>>
> 
>