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

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Date:   Sun, 13 Feb 2022 19:50:55 +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 18:59, Jonathan Cameron a écrit :
> On Wed,  9 Feb 2022 00:37:53 -0800
> Qing Wang <wangqing@...o.com> wrote:
> 
>> From: Wang Qing <wangqing@...o.com>
>>
>> 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@...o.com>
> 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@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 =
> 
>