From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from smtp-vbr1.xs4all.nl ([194.109.24.21]:4376 "EHLO smtp-vbr1.xs4all.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750852AbaBUHRs (ORCPT ); Fri, 21 Feb 2014 02:17:48 -0500 Message-ID: <5306FD7F.6070207@xs4all.nl> Date: Fri, 21 Feb 2014 08:17:19 +0100 From: Hans Verkuil MIME-Version: 1.0 To: Laurent Pinchart CC: Sakari Ailus , linux-media@vger.kernel.org, k.debski@samsung.com Subject: Re: [PATCH v5.1 3/7] v4l: Add timestamp source flags, mask and document them References: <20140217232931.GW15635@valkosipuli.retiisi.org.uk> <1392925276-20412-1-git-send-email-sakari.ailus@iki.fi> <53066763.3070000@xs4all.nl> <1806212.4rVLkqN7y6@avalon> In-Reply-To: <1806212.4rVLkqN7y6@avalon> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: On 02/21/2014 12:30 AM, Laurent Pinchart wrote: > Hi Hans, > > On Thursday 20 February 2014 21:36:51 Hans Verkuil wrote: >> On 02/20/2014 08:41 PM, Sakari Ailus wrote: >>> Some devices do not produce timestamps that correspond to the end of the >>> frame. The user space should be informed on the matter. This patch >>> achieves >>> that by adding buffer flags (and a mask) for timestamp sources since more >>> possible timestamping points are expected than just two. >>> >>> A three-bit mask is defined (V4L2_BUF_FLAG_TSTAMP_SRC_MASK) and two of the >>> eight possible values is are defined V4L2_BUF_FLAG_TSTAMP_SRC_EOF for end >>> of frame (value zero) V4L2_BUF_FLAG_TSTAMP_SRC_SOE for start of exposure >>> (next value). >> >> Sorry, but I still have two small notes: >>> Signed-off-by: Sakari Ailus >>> --- >>> since v5: >>> - Add a note on software generated timestamp inaccuracy. >>> >>> Documentation/DocBook/media/v4l/io.xml | 38 +++++++++++++++++++++---- >>> drivers/media/v4l2-core/videobuf2-core.c | 4 +++- >>> include/media/videobuf2-core.h | 2 ++ >>> include/uapi/linux/videodev2.h | 4 ++++ >>> 4 files changed, 41 insertions(+), 7 deletions(-) >>> >>> diff --git a/Documentation/DocBook/media/v4l/io.xml >>> b/Documentation/DocBook/media/v4l/io.xml index 46d24b3..22b87bc 100644 >>> --- a/Documentation/DocBook/media/v4l/io.xml >>> +++ b/Documentation/DocBook/media/v4l/io.xml >>> @@ -653,12 +653,6 @@ plane, are stored in struct >>> v4l2_plane instead.> >>> In that case, struct v4l2_buffer contains an >>> array of plane structures. >>> >>> - For timestamp types that are sampled from the system clock >>> -(V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC) it is guaranteed that the timestamp >>> is >>> -taken after the complete frame has been received (or transmitted in >>> -case of video output devices). For other kinds of >>> -timestamps this may vary depending on the driver. >>> - >>> >>> >>> >>> struct <structname>v4l2_buffer</structname> >>> >>> >>> @@ -1119,6 +1113,38 @@ in which case caches have not been used. >>> The CAPTURE buffer timestamp has been taken from the >>> corresponding OUTPUT buffer. This flag applies only to mem2mem >>> devices. >>> >>> + >>> + V4L2_BUF_FLAG_TSTAMP_SRC_MASK >>> + 0x00070000 >>> + Mask for timestamp sources below. The timestamp source >>> + defines the point of time the timestamp is taken in relation to >>> + the frame. Logical and operation between the >>> + flags field and >>> + V4L2_BUF_FLAG_TSTAMP_SRC_MASK produces the >>> + value of the timestamp source. >>> + >>> + >>> + V4L2_BUF_FLAG_TSTAMP_SRC_EOF >>> + 0x00000000 >>> + End Of Frame. The buffer timestamp has been taken >>> + when the last pixel of the frame has been received or the >>> + last pixel of the frame has been transmitted. In practice, >>> + software generated timestamps will typically be read from >>> + the clock a small amount of time after the last pixel has >>> + been received, depending on the system and other activity >> >> s/been received/been received or transmitted/ >> >>> + in it. >>> + >>> + >>> + V4L2_BUF_FLAG_TSTAMP_SRC_SOE >>> + 0x00010000 >>> + Start Of Exposure. The buffer timestamp has been >>> + taken when the exposure of the frame has begun. In >>> + practice, software generated timestamps will typically be >>> + read from the clock a small amount of time after the last >>> + pixel has been received, depending on the system and other >>> + activity in it. This is only valid for buffer type >>> + V4L2_BUF_TYPE_VIDEO_CAPTURE. >> >> I would move the last sentence up to just before "In practice...". The >> way it is now it looks like an afterthought. >> >> I am also not sure whether the whole "In practice" sentence is valid >> here. Certainly the bit about "the last pixel" isn't since this is the >> "SOE" case and not the End Of Frame. In the case of the UVC driver (and >> that's the only one using this timestamp source) the timestamps come from >> the hardware as I understand it, so the "software generated" bit doesn't >> apply. >> >> I would actually be inclined to drop it altogether for this particular >> timestamp source. But it's up to Laurent. > > What do you mean, drop what altogether ? The "In practice ... activity in it." sentence. Regards, Hans > >>> + >>> >>> >>>
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