Date: Sat, 11 Mar 2017 00:30:09 +0100
From: Pavel Machek <pavel@ucw.cz>
To: Steve Longerbeam <slongerbeam@gmail.com>
Cc: Hans Verkuil <hverkuil@xs4all.nl>, robh+dt@kernel.org,
        mark.rutland@arm.com, shawnguo@kernel.org, kernel@pengutronix.de,
        fabio.estevam@nxp.com, linux@armlinux.org.uk, mchehab@kernel.org,
        nick@shmanahar.org, markus.heiser@darmarIT.de, p.zabel@pengutronix.de,
        laurent.pinchart+renesas@ideasonboard.com, bparrot@ti.com,
        geert@linux-m68k.org, arnd@arndb.de, sudipm.mukherjee@gmail.com,
        minghsiu.tsai@mediatek.com, tiffany.lin@mediatek.com,
        jean-christophe.trotin@st.com, horms+renesas@verge.net.au,
        niklas.soderlund+renesas@ragnatech.se, robert.jarzmik@free.fr,
        songjun.wu@microchip.com, andrew-ct.chen@mediatek.com,
        gregkh@linuxfoundation.org, shuah@kernel.org,
        sakari.ailus@linux.intel.com, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-media@vger.kernel.org, devel@driverdev.osuosl.org
Subject: Re: [PATCH v5 15/39] [media] v4l2: add a frame interval error event
Message-ID: <20170310233008.GC6540@amd>
References: <1489121599-23206-1-git-send-email-steve_longerbeam@mentor.com>
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 <5b0a0e76-2524-4140-5ccc-380a8f949cfa@xs4all.nl>
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On Fri 2017-03-10 10:37:21, Steve Longerbeam wrote:
> Hi Hans,
>=20
> On 03/10/2017 04:03 AM, Hans Verkuil wrote:
> >On 10/03/17 05:52, Steve Longerbeam wrote:
> >>Add a new FRAME_INTERVAL_ERROR event to signal that a video capture or
> >>output device has measured an interval between the reception or transmit
> >>completion of two consecutive frames of video that is outside the nomin=
al
> >>frame interval by some tolerance value.
> >
> >Reading back what was said on this I agree with Sakari that this doesn't
> >belong here.
> >
> >Userspace can detect this just as easily (if not easier) with a timeout.
> >
>=20
>=20
> Unfortunately measuring frame intervals from userland is not accurate
> enough for i.MX6.
>=20
> The issue here is that the IPUv3, specifically the CSI unit, can
> permanently lose vertical sync if there are truncated frames sent
> on the bt.656 bus. We have seen a single missing line of video cause
> loss of vertical sync. The only way to correct this is to shutdown
> the IPU capture hardware and restart, which can be accomplished
> simply by restarting streaming from userland.
>=20
> There are no other indicators from the sensor about these short
> frame events (believe me, we've exhausted all avenues with the ADV718x).
> And the IPUv3 DMA engine has no status indicators for short frames
> either. So the only way to detect them is by measuring frame intervals.
>=20
> The intervals have to be able to resolve a single line of missing video.
> With a PAL video source that requires better than 58 usec accuracy.
>=20
> There is too much uncertainty to resolve this at user level. The
> driver is able to resolve this by measuring intervals between hardware
> interrupts as long as interrupt latency is reasonably low, and we
> have another method using the i.MX6 hardware input capture support
> that can measure these intervals very accurately with no errors
> introduced by interrupt latency.

Requiring < 58 usec interrupt latency for correct operation is a
little too optimistic, no?
									Pavel
--=20
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo=
g.html

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