linux-kernel - Re: [PATCH] drm/msm: avoid using 'timespec'

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Date:   Tue, 10 Jul 2018 23:27:00 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Sean Paul <seanpaul@...omium.org>
Cc:     Rob Clark <robdclark@...il.com>, David Airlie <airlied@...ux.ie>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        linux-arm-msm@...r.kernel.org,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno@...ts.freedesktop.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm: avoid using 'timespec'

On Tue, Jul 10, 2018 at 10:47 PM, Sean Paul <seanpaul@...omium.org> wrote:
> On Mon, Jun 18, 2018 at 05:39:42PM +0200, Arnd Bergmann wrote:
>> The timespec structure and associated interfaces are deprecated and will
>> be removed in the future because of the y2038 overflow.
>>
>> The use of ktime_to_timespec() in timeout_to_jiffies() does not
>> suffer from that overflow, but is easy to avoid by just converting
>> the ktime_t into jiffies directly.
>>
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>> ---
>>  drivers/gpu/drm/msm/msm_drv.h | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
>> index b2da1fbf81e0..cc8977476a41 100644
>> --- a/drivers/gpu/drm/msm/msm_drv.h
>> +++ b/drivers/gpu/drm/msm/msm_drv.h
>> @@ -353,8 +353,7 @@ static inline unsigned long timeout_to_jiffies(const ktime_t *timeout)
>>               remaining_jiffies = 0;
>>       } else {
>>               ktime_t rem = ktime_sub(*timeout, now);
>> -             struct timespec ts = ktime_to_timespec(rem);
>> -             remaining_jiffies = timespec_to_jiffies(&ts);
>> +             remaining_jiffies = ktime_divns(rem, NSEC_PER_SEC / HZ);
>
> Do you need to wrap rem in ktime_to_ns() just to be safe?

The ktime_t interfaces are still defined to use an opaque type,
as previously it was a union that could be a seconds/nanoseconds
pair depending on the architecture. These days, ktime_t is just
a 64-bit integer, so div_u64() would work just as well as ktime_divns(),
but this is the documented way to do it.

      Arnd