From: Tomasz Figa <tfiga@chromium.org>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Heng-Ruey Hsu <henryhsu@chromium.org>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Linux Media Mailing List <linux-media@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Ricky Liang <jcliang@chromium.org>
Subject: Re: [PATCH] media: uvcvideo: Add boottime clock support
Date: Wed, 17 Oct 2018 17:28:52 +0900 [thread overview]
Message-ID: <CAAFQd5B+4x4aSUywtdukwgUmQNQsQsbK4sjedNphwNFteaTscg@mail.gmail.com> (raw)
In-Reply-To: <13883852.6N9L7C0n48@avalon>
Hi Laurent,
On Wed, Oct 17, 2018 at 5:02 PM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Heng-Ruey,
>
> Thank you for the patch.
>
> 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.
Generally, I'd see a V4L2_BUF_FLAG_TIMESTAMP_BOOTTIME flag being added
and user space being given choice to select the time stamp base it
needs, perhaps by setting the flag in v4l2_buffer struct at QBUF time?
Best regards,
Tomasz
> > Signed-off-by: Heng-Ruey Hsu <henryhsu@chromium.org>
> > ---
> > drivers/media/usb/uvc/uvc_driver.c | 4 ++++
> > drivers/media/usb/uvc/uvc_video.c | 2 ++
> > 2 files changed, 6 insertions(+)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_driver.c
> > b/drivers/media/usb/uvc/uvc_driver.c index d46dc432456c..a9658f38c586
> > 100644
> > --- a/drivers/media/usb/uvc/uvc_driver.c
> > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > @@ -2287,6 +2287,8 @@ static int uvc_clock_param_get(char *buffer, const
> > struct kernel_param *kp) {
> > if (uvc_clock_param == CLOCK_MONOTONIC)
> > return sprintf(buffer, "CLOCK_MONOTONIC");
> > + else if (uvc_clock_param == CLOCK_BOOTTIME)
> > + return sprintf(buffer, "CLOCK_BOOTTIME");
> > else
> > return sprintf(buffer, "CLOCK_REALTIME");
> > }
> > @@ -2298,6 +2300,8 @@ static int uvc_clock_param_set(const char *val, const
> > struct kernel_param *kp)
> >
> > if (strcasecmp(val, "monotonic") == 0)
> > uvc_clock_param = CLOCK_MONOTONIC;
> > + else if (strcasecmp(val, "boottime") == 0)
> > + uvc_clock_param = CLOCK_BOOTTIME;
> > else if (strcasecmp(val, "realtime") == 0)
> > uvc_clock_param = CLOCK_REALTIME;
> > else
> > diff --git a/drivers/media/usb/uvc/uvc_video.c
> > b/drivers/media/usb/uvc/uvc_video.c index 86a99f461fd8..d4248d5cd9cd 100644
> > --- a/drivers/media/usb/uvc/uvc_video.c
> > +++ b/drivers/media/usb/uvc/uvc_video.c
> > @@ -425,6 +425,8 @@ static inline ktime_t uvc_video_get_time(void)
> > {
> > if (uvc_clock_param == CLOCK_MONOTONIC)
> > return ktime_get();
> > + else if (uvc_clock_param == CLOCK_BOOTTIME)
> > + return ktime_get_boottime();
> > else
> > return ktime_get_real();
> > }
>
> --
> Regards,
>
> Laurent Pinchart
>
>
>
next prev parent reply other threads:[~2018-10-17 16:23 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-17 7:52 [PATCH] media: uvcvideo: Add boottime clock support Heng-Ruey Hsu
2018-10-17 8:02 ` Laurent Pinchart
2018-10-17 8:28 ` Tomasz Figa [this message]
2018-10-17 20:50 ` Laurent Pinchart
2018-10-18 4:31 ` Tomasz Figa
2018-10-18 17:28 ` Alexandru M Stan
2018-11-01 14:03 ` Laurent Pinchart
2018-11-01 14:30 ` Tomasz Figa
2018-11-01 15:03 ` Lars-Peter Clausen
2018-11-23 14:46 ` Tomasz Figa
2019-03-06 6:09 ` Tomasz Figa
2019-03-13 1:24 ` Laurent Pinchart
2019-03-13 2:38 ` Tomasz Figa
2019-08-06 4:15 ` Tomasz Figa
2019-08-06 8:34 ` Kieran Bingham
2019-08-07 13:38 ` Tomasz Figa
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