linux-kernel - Re: [PATCH] power: supply: da9150: use div64_u64() instead of do

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Message-ID: <9b563415-f58a-15f1-b375-64ef4e98ca05@wanadoo.fr>
Date:   Fri, 11 Feb 2022 21:53:08 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Sebastian Reichel <sebastian.reichel@...labora.com>,
        Qing Wang <wangqing@...o.com>
Cc:     Support Opensource <support.opensource@...semi.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] power: supply: da9150: use div64_u64() instead of
 do_div()

Le 11/02/2022 à 21:50, Sebastian Reichel a écrit :
> Hi,
> 
> On Wed, Feb 09, 2022 at 12:39:46AM -0800, Qing Wang 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>
>> ---
> 
> Thanks, queued.

All these patches are broken and should be NACKed, fixed or reverted if 
applied.

See [1].

CJ

[1]: 
https://lore.kernel.org/linux-kernel/19b96972-cee7-937f-21ce-c78982ed2048@linaro.org/

> 
> -- Sebastian
> 
>>   drivers/power/supply/da9150-fg.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/power/supply/da9150-fg.c b/drivers/power/supply/da9150-fg.c
>> index 6e36782..896491a
>> --- a/drivers/power/supply/da9150-fg.c
>> +++ b/drivers/power/supply/da9150-fg.c
>> @@ -250,7 +250,7 @@ static int da9150_fg_current_avg(struct da9150_fg *fg,
>>   	div = (u64) (sd_gain * shunt_val * 65536ULL);
>>   	do_div(div, 1000000);
>>   	res = (u64) (iavg * 1000000ULL);
>> -	do_div(res, div);
>> +	div64_u64(res, div);
>>   
>>   	val->intval = (int) res;
>>   
>> -- 
>> 2.7.4
>>