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Message-ID: <20240610114306.GR18479@pendragon.ideasonboard.com>
Date: Mon, 10 Jun 2024 14:43:06 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Tomasz Figa <tfiga@...omium.org>
Cc: Ricardo Ribalda <ribalda@...omium.org>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
"hn.chen" <hn.chen@...plusit.com>,
Hans Verkuil <hverkuil@...all.nl>,
Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v10 4/6] media: uvcvideo: Allow hw clock updates with
buffers not full
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@...plusit.com>
> > Reviewed-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> > Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> > 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.
> Anyway:
>
> Reviewed-by: Tomasz Figa <tfiga@...omium.org>
--
Regards,
Laurent Pinchart
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