linux-kernel - Re: [PATCH] media: rc: Replace timeval with ktime

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Date:	Thu, 18 Dec 2014 17:38:14 +0800
From:	Chunyan Zhang <zhang.chunyan@...aro.org>
To:	Arnd Bergmann <arnd@...aro.org>
Cc:	m.chehab@...sung.com, david@...deman.nu, uli-lirc@...-eckhardt.de,
	hans.verkuil@...co.com, julia.lawall@...6.fr,
	Himangi Saraogi <himangi774@...il.com>,
	Alexey Khoroshilov <khoroshilov@...ras.ru>, joe@...ches.com,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	Lyra Zhang <zhang.lyra@...il.com>
Subject: Re: [PATCH] media: rc: Replace timeval with ktime_t in imon.c

On Thu, Dec 18, 2014 at 3:50 PM, Arnd Bergmann <arnd@...aro.org> wrote:
> On Thursday 18 December 2014 11:37:13 Chunyan Zhang wrote:
>> This patch changes the 32-bit time type (timeval) to the 64-bit one
>> (ktime_t), since 32-bit time types will break in the year 2038.
>>
>> I use ktime_t instead of all uses of timeval in imon.c
>>
>> This patch also changes do_gettimeofday() to ktime_get() accordingly,
>> since ktime_get returns a ktime_t, but do_gettimeofday returns a
>> struct timeval, and the other reason is that ktime_get() uses
>> the monotonic clock.
>>
>> This patch use a new function which is provided by another patch listed below
>> to get the millisecond time difference.
>
> The patch looks great. Just a few small details that could still be
> improved:
>
>> http://lkml.iu.edu//hypermail/linux/kernel/1412.2/00625.html
>>
>> Signed-off-by: Chunyan Zhang <zhang.chunyan@...aro.org>
>
> In general, when you give a mailing list link, use the 'Link' tag
> under your Signed-off-by line, like
>
> Link: http://lkml.iu.edu//hypermail/linux/kernel/1412.2/00625.html
>
> It's not used much yet, but getting more popular and seems useful to me.
>
> In this particular case, when you have patches that depend on one
> another, you can make do it even better by sending all three patches
> as a series with a [PATCH 0/3] cover letter.
>
OK, I'll send a patch-set including these three patches

> If the media maintainers can provide an Ack for this patch, I would
> suggest to queue it up in the y2038 branch together with your first
> patch that it depends on.
>
>> @@ -1191,16 +1168,16 @@ static inline int tv2int(const struct timeval *a, const struct timeval *b)
>>   */
>>  static int stabilize(int a, int b, u16 timeout, u16 threshold)
>>  {
>> -     struct timeval ct;
>> -     static struct timeval prev_time = {0, 0};
>> -     static struct timeval hit_time  = {0, 0};
>> +     ktime_t ct;
>> +     static ktime_t prev_time = {0};
>> +     static ktime_t hit_time  = {0};
>>       static int x, y, prev_result, hits;
>>       int result = 0;
>
> The "= {0}" part here is redundant, since static variables are always
> initialized to zero. Normally, adding the explicit initializer can
> help readability, but in this case I would leave it out because it shows
> implementation details of ktime_t that are better hidden from drivers.
>
OK, I'll modify them soon

Thanks,
Chunyan

>> @@ -1596,9 +1573,9 @@ static void imon_incoming_packet(struct imon_context *ictx,
>>       int i;
>>       u64 scancode;
>>       int press_type = 0;
>> -     int msec;
>> -     struct timeval t;
>> -     static struct timeval prev_time = { 0, 0 };
>> +     long msec;
>> +     ktime_t t;
>> +     static ktime_t prev_time = {0};
>>       u8 ktype;
>
> Same thing here of course.
>
>         Arnd
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