On Mon, Jun 10, 2024 at 8:43 PM Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > On Wed, May 29, 2024 at 05:03:08PM +0900, Tomasz Figa wrote: > > On Sat, Mar 23, 2024 at 10:48:05AM +0000, Ricardo Ribalda wrote: > > > With UVC 1.5 we get as little as one clock sample per frame. Which means > > > that it takes 32 frames to move from the software timestamp to the > > > hardware timestamp method. > > > > > > This results in abrupt changes in the timestamping after 32 frames (~1 > > > second), resulting in noticeable artifacts when used for encoding. > > > > > > With this patch we modify the update algorithm to work with whatever > > > amount of values are available. > > > > > > Tested-by: HungNien Chen <hn.chen@xxxxxxxxxxxxx> > > > Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx> > > > Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > > > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx> > > > --- > > > drivers/media/usb/uvc/uvc_video.c | 16 ++++++++++++++-- > > > 1 file changed, 14 insertions(+), 2 deletions(-) > > > > > > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c > > > index d6ca383f643e3..af25b9f1b53fe 100644 > > > --- a/drivers/media/usb/uvc/uvc_video.c > > > +++ b/drivers/media/usb/uvc/uvc_video.c > > > @@ -768,10 +768,10 @@ void uvc_video_clock_update(struct uvc_streaming *stream, > > > > > > spin_lock_irqsave(&clock->lock, flags); > > > > > > - if (clock->count < clock->size) > > > + if (clock->count < 2) > > > goto done; > > > > > > - first = &clock->samples[clock->head]; > > > + first = &clock->samples[(clock->head - clock->count + clock->size) % clock->size]; > > > last = &clock->samples[(clock->head - 1 + clock->size) % clock->size]; > > > > > > /* First step, PTS to SOF conversion. */ > > > @@ -786,6 +786,18 @@ void uvc_video_clock_update(struct uvc_streaming *stream, > > > if (y2 < y1) > > > y2 += 2048 << 16; > > > > > > + /* > > > + * Have at least 1/4 of a second of timestamps before we > > > + * try to do any calculation. Otherwise we do not have enough > > > + * precision. This value was determined by running Android CTS > > > + * on different devices. > > > + * > > > + * dev_sof runs at 1KHz, and we have a fixed point precision of > > > + * 16 bits. > > > + */ > > > + if ((y2 - y1) < ((1000 / 4) << 16)) > > > + goto done; > > > > Not a comment for this patch directly, but... > > > > This kind of makes me wonder if we don't want to have some documentation > > that specifies what the userspace can expect from the timestamps, so > > that this isn't changed randomly in the future breaking what was fixed > > by this patch. > > I think timestamp handling should really be moved to userspace. It will > be easier to handle with floating-point arithmetic there. That would > have been difficult to manage for applications a while ago, but now that > we have libcamera, we could implement it there. This isn't high on my > todo list though. While indeed that would probably be a better way to handle the complex logic if we designed the driver today, we already have userspace that expects the timestamps to be handled correctly in the kernel. I suspect moving it to the userspace would require some core V4L2 changes to define a new timestamp handling mode, where multiple raw hardware timestamps are exposed to the userspace, instead of the high level system monotonic one. Best regards, Tomasz
