On Wednesday 06 May 2015 17:58:01 Hans Verkuil wrote: > > On 05/04/2015 12:14 PM, Arnd Bergmann wrote: > > On Monday 04 May 2015 09:42:36 Hans Verkuil wrote: > >> Ping! (Added Arnd to the CC list) > > > > Hi Hans, > > > > sorry I missed this the first time > > > >> On 04/27/2015 09:40 AM, Hans Verkuil wrote: > >>> Added the y2038 mailinglist since I would like to get their input for > >>> this API. > >>> > >>> Y2038 experts, can you take a look at my comment in the code below? > >>> > >>> Thanks! > >> > >> Arnd, I just saw your patch series adding struct __kernel_timespec to > >> uapi/linux/time.h. I get the feeling that it might take a few kernel > >> cycles before we have a timespec64 available in userspace. Based on that > >> I think this CEC API should drop the timestamps for now and wait until > >> timespec64 becomes available before adding it. > >> > >> The timestamps are a nice-to-have, but not critical. So adding it later > >> shouldn't be a problem. What is your opinion? > > > > It will take a little while for the patches to make it in, I would guess > > 4.3 at the earliest. Using your own struct works just as well and would > > be less ambiguous. > > > > However, for timestamps, I would recommend not using timespec anyway. > > Instead, just use a single 64-bit nanosecond value from ktime_get_ns() > > (or ktime_get_boot_ns() if you need a time that keeps ticking across > > suspend). This is more efficient to get and simpler to use as long > > as you don't need to convert from nanosecond to timespec. > > Possibly stupid follow-up question: > > is ktime_get_ns() just a different representation as ktime_get_ts64()? Yes. > Or is there some offset between the two? They seem to be identical based > on a quick test, but I'd like to be certain that that's always the case. > > Users need to be able to relate this timestamp to a struct timespec as > returned by V4L2 (and others). * ktime_get_ns() uses the same timebase as ktime_get_ts64(). * ktime_get_boot_ns() uses the same timebase as ktime_get_boottime() or getboottime64(), which differs from the first after suspend * ktime_get_real_ns() uses the same time as gettimeofday() in user space, which is always different from the other two. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
