From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from perceval.ideasonboard.com ([95.142.166.194]:51094 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752516Ab1LWL25 (ORCPT ); Fri, 23 Dec 2011 06:28:57 -0500 From: Laurent Pinchart To: Marek Szyprowski Subject: Re: MEM2MEM devices: how to handle sequence number? Date: Fri, 23 Dec 2011 12:28:44 +0100 Cc: "'javier Martin'" , linux-media@vger.kernel.org, s.nawrocki@samsung.com, hverkuil@xs4all.nl, kyungmin.park@samsung.com, shawn.guo@linaro.org, richard.zhao@linaro.org, fabio.estevam@freescale.com, kernel@pengutronix.de, s.hauer@pengutronix.de, r.schwebel@pengutronix.de, "'Pawel Osciak'" References: <013f01ccc141$cdf78ed0$69e6ac70$%szyprowski@samsung.com> In-Reply-To: <013f01ccc141$cdf78ed0$69e6ac70$%szyprowski@samsung.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201112231228.45439.laurent.pinchart@ideasonboard.com> Sender: linux-media-owner@vger.kernel.org List-ID: Hi Marek, On Friday 23 December 2011 08:09:25 Marek Szyprowski wrote: > On Thursday, December 22, 2011 3:34 PM Javier Martin wrote: > > we have a processing chain composed of three v4l2 devices: > > > > --------------------- ----------------------- > > ---------------------- > > > > | v4l2 source | | v4l2 fixer | | v4l2 > > | encoder | > > | > > | (capture) |---------->| (mem2mem)| ------------>| (mem2mem) | > > > > ------------> > > > > |___________| |____________| |____________| > > > > "v4l2 source" generates consecutive sequence numbers so that we can > > detect whether a frame has been lost or not. > > "v4l2 fixer" and "v4l2 encoder" cannot lose frames because they don't > > interact with an external sensor. > > > > How should "v4l2 fixer" and "v4l2 encoder" behave regarding frame > > sequence number? Should they just copy the sequence number from the > > input buffer to the output buffer or should they maintain their own > > count for the CAPTURE queue? > > IMHO mem2mem devices, which process buffers in 1:1 way (there is always > exactly one 'capture'/destination buffer for every 'output'/source buffer) > can simply copy the sequence number from the source buffer to the > destination. > > If there is no such 1:1 mapping between the buffers, drivers should > maintain their own numbers. video encoder is probably an example of such > device. A single destination ('capture') buffer with encoded video data > might contain a fraction, one or more source ('output') video > buffers/frames. > > > If the former option is chosen we should apply a patch like the > > following so that the sequence number of the input buffer is passed to > > the videobuf2 layer: > > > > diff --git a/drivers/media/video/videobuf2-core.c > > b/drivers/media/video/videobuf2-core.c > > index 1250662..7d8a88b 100644 > > --- a/drivers/media/video/videobuf2-core.c > > +++ b/drivers/media/video/videobuf2-core.c > > @@ -1127,6 +1127,7 @@ int vb2_qbuf(struct vb2_queue *q, struct > > v4l2_buffer *b) > > */ > > list_add_tail(&vb->queued_entry, &q->queued_list); > > vb->state = VB2_BUF_STATE_QUEUED; > > + vb->v4l2_buf.sequence = b->sequence; > > /* > > * If already streaming, give the buffer to driver for > > processing. > > Right, such patch is definitely needed. Please resend it with > 'signed-off-by' annotation. I'm not too sure about that. Isn't the sequence number supposed to be ignored by drivers on video output devices ? The documentation is a bit terse on the subject, all it says is __u32 sequence Set by the driver, counting the frames in the sequence. -- Regards, Laurent Pinchart