On Fri, Nov 23, 2018 at 11:46 PM Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote: > > Hi Laurent, > > On Fri, Nov 2, 2018 at 12:03 AM Lars-Peter Clausen <lars@xxxxxxxxxx> wrote: > > > > On 11/01/2018 03:30 PM, Tomasz Figa wrote: > > > On Thu, Nov 1, 2018 at 11:03 PM Laurent Pinchart > > > <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > >> > > >> Hi Alexandru, > > >> > > >> On Thursday, 18 October 2018 20:28:06 EET Alexandru M Stan wrote: > > >>> On Wed, Oct 17, 2018 at 9:31 PM, Tomasz Figa wrote: > > >>>> On Thu, Oct 18, 2018 at 5:50 AM Laurent Pinchart wrote: > > >>>>> On Wednesday, 17 October 2018 11:28:52 EEST Tomasz Figa wrote: > > >>>>>> On Wed, Oct 17, 2018 at 5:02 PM Laurent Pinchart wrote: > > >>>>>>> On Wednesday, 17 October 2018 10:52:42 EEST Heng-Ruey Hsu wrote: > > >>>>>>>> Android requires camera timestamps to be reported with > > >>>>>>>> CLOCK_BOOTTIME to sync timestamp with other sensor sources. > > >>>>>>> > > >>>>>>> What's the rationale behind this, why can't CLOCK_MONOTONIC work ? If > > >>>>>>> the monotonic clock has shortcomings that make its use impossible for > > >>>>>>> proper synchronization, then we should consider switching to > > >>>>>>> CLOCK_BOOTTIME globally in V4L2, not in selected drivers only. > > >>>>>> > > >>>>>> CLOCK_BOOTTIME includes the time spent in suspend, while > > >>>>>> CLOCK_MONOTONIC doesn't. I can imagine the former being much more > > >>>>>> useful for anything that cares about the actual, long term, time > > >>>>>> tracking. Especially important since suspend is a very common event on > > >>>>>> Android and doesn't stop the time flow there, i.e. applications might > > >>>>>> wake up the device to perform various tasks at necessary times. > > >>>>> > > >>>>> Sure, but this patch mentions timestamp synchronization with other > > >>>>> sensors, and from that point of view, I'd like to know what is wrong with > > >>>>> the monotonic clock if all devices use it. > > >>>> > > >>>> AFAIK the sensors mentioned there are not camera sensors, but rather > > >>>> things we normally put under IIO, e.g. accelerometers, gyroscopes and > > >>>> so on. I'm not sure how IIO deals with timestamps, but Android seems > > >>>> to operate in the CLOCK_BOTTIME domain. Let me add some IIO folks. > > >>>> > > >>>> Gwendal, Alexandru, do you think you could shed some light on how we > > >>>> handle IIO sensors timestamps across the kernel, Chrome OS and > > >>>> Android? > > >>> > > >>> On our devices of interest have a specialized "sensor" that comes via > > >>> IIO (from the EC, cros-ec-ring driver) that can be used to more > > >>> accurately timestamp each frame (since it's recorded with very low > > >>> jitter by a realtime-ish OS). In some high level userspace thing > > >>> (specifically the Android Camera HAL) we try to pick the best > > >>> timestamp from the IIO, whatever's closest to what the V4L stuff gives > > >>> us. > > >>> > > >>> I guess the Android convention is for sensor timestamps to be in > > >>> CLOCK_BOOTTIME (maybe because it likes sleeping so much). There's > > >>> probably no advantage to using one over the other, but the important > > >>> thing is that they have to be the same, otherwise the closest match > > >>> logic would fail. > > >> > > >> That's my understanding too, I don't think CLOCK_BOOTTIME really brings much > > >> benefit in this case, > > > > > > I think it does have a significant benefit. CLOCK_MONOTONIC stops when > > > the device is sleeping, but the sensors can still capture various > > > actions. We would lose the time keeping of those actions if we use > > > CLOCK_MONOTONIC. > > > > > >> but it's important than all timestamps use the same > > >> clock. The question is thus which clock we should select. Mainline mostly uses > > >> CLOCK_MONOTONIC, and Android CLOCK_BOOTTIME. Would you like to submit patches > > >> to switch Android to CLOCK_MONOTONIC ? :-) > > > > > > Is it Android using CLOCK_BOOTTIME or the sensors (IIO?). I have > > > almost zero familiarity with the IIO subsystem and was hoping someone > > > from there could comment on what time domain is used for those > > > sensors. > > > > IIO has the option to choose between BOOTTIME or MONOTONIC (and a few > > others) for the timestamp on a per device basis. > > > > There was a bit of a discussion about this a while back. See > > https://lkml.org/lkml/2018/7/10/432 and the following thread. > > Given that IIO supports BOOTTIME in upstream already and also the > important advantage of using it over MONOTONIC for systems which keep > capturing events during sleep, do you think we could move on with some > way to support it in uvcvideo or preferably V4L2 in general? Gentle ping. Best regards, Tomasz
