linux-kernel - Re: [PATCH v2] kernel/power/hibernate.c: use 'u64' instead of 's64' to avoid warning

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Date:	Tue, 22 Apr 2014 15:56:55 +0800
From:	Chen Gang <gang.chen.5i5j@...il.com>
To:	Pavel Machek <pavel@....cz>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Guan Xuetao <gxt@...c.pku.edu.cn>, len.brown@...el.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v2] kernel/power/hibernate.c: use 'u64' instead of 's64'
 to avoid warning

On 04/22/2014 03:21 PM, Pavel Machek wrote:
> On Tue 2014-04-22 09:29:20, Chen Gang wrote:
>> For do_div(), it need 'u64' type, which means the outside must be sure
>> of 'start' is not bigger than 'stop', or it will report warning.
>>
>> Even if 'start' was really bigger than 'stop', it would print incorrect
>> information, but for kernel, it still can continue, so use WARN_ON() is
>> enough.
>>
>> The related warning (with allmodconfig for unicore32):
>>
>>     CC      kernel/power/hibernate.o
>>   kernel/power/hibernate.c: In function ‘swsusp_show_speed’:
>>   kernel/power/hibernate.c:237: warning: comparison of distinct pointer types lacks a cast
>>
>>
> 
> Certainly better, but
> 
>> -	s64 elapsed_centisecs64;
>> +	u64 elapsed_centisecs64;
>>  	int centisecs;
>>  	int k;
>>  	int kps;
>>  
>>  	elapsed_centisecs64 = timeval_to_ns(stop) - timeval_to_ns(start);
>> +	WARN_ON((s64)elapsed_centisecs64 < 0);
>>  	do_div(elapsed_centisecs64, NSEC_PER_SEC / 100);
>>  	centisecs = elapsed_centisecs64;
> 
> ...do we need to do the WARN_ON()? Only result of underflow will be
> very long elapsed time reported... that does not sound too
> bad. ... and it will be quite obvious what went wrong.
> 									Pavel
> 

Hmm... that sounds reasonable to me.  If no any other reply within 2
days, I shall send patch v3 for it.

BTW: sorry, I guess I can not finish allmodconfig for unicore32 within
this month (2014-04-30) -- at present I only finish 40-50%, I
will/should try to finish it within next month.


Thanks.
-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed
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