linux-kernel - Re: [PATCH 5/8] media: cedrus: Detect first slice of a frame

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Date:   Mon, 26 Aug 2019 20:47:57 +0200
From:   Jernej Škrabec <jernej.skrabec@...l.net>
To:     Boris Brezillon <boris.brezillon@...labora.com>
Cc:     mchehab@...nel.org, hverkuil-cisco@...all.nl,
        paul.kocialkowski@...tlin.com, mripard@...nel.org,
        pawel@...iak.com, m.szyprowski@...sung.com,
        kyungmin.park@...sung.com, tfiga@...omium.org, wens@...e.org,
        acourbot@...omium.org, gregkh@...uxfoundation.org,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-arm-kernel@...ts.infradead.org,
        ezequiel@...labora.com, jonas@...boo.se
Subject: Re: [PATCH 5/8] media: cedrus: Detect first slice of a frame

Dne ponedeljek, 26. avgust 2019 ob 20:28:31 CEST je Boris Brezillon 
napisal(a):
> Hi Jernej,
> 
> On Thu, 22 Aug 2019 21:44:57 +0200
> 
> Jernej Skrabec <jernej.skrabec@...l.net> wrote:
> > When codec supports multiple slices in one frame, VPU has to know when
> > first slice of each frame is being processed, presumably to correctly
> > clear/set data in auxiliary buffers.
> > 
> > Add first_slice field to cedrus_run structure and set it according to
> > timestamps of capture and output buffers. If timestamps are different,
> > it's first slice and viceversa.
> > 
> > Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> > ---
> > 
> >  drivers/staging/media/sunxi/cedrus/cedrus.h     | 1 +
> >  drivers/staging/media/sunxi/cedrus/cedrus_dec.c | 2 ++
> >  2 files changed, 3 insertions(+)
> > 
> > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.h
> > b/drivers/staging/media/sunxi/cedrus/cedrus.h index
> > 2f017a651848..32cb38e541c6 100644
> > --- a/drivers/staging/media/sunxi/cedrus/cedrus.h
> > +++ b/drivers/staging/media/sunxi/cedrus/cedrus.h
> > @@ -70,6 +70,7 @@ struct cedrus_mpeg2_run {
> > 
> >  struct cedrus_run {
> >  
> >  	struct vb2_v4l2_buffer	*src;
> >  	struct vb2_v4l2_buffer	*dst;
> > 
> > +	bool first_slice;
> > 
> >  	union {
> >  	
> >  		struct cedrus_h264_run	h264;
> > 
> > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> > b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c index
> > 56ca4c9ad01c..d7b54accfe83 100644
> > --- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> > @@ -31,6 +31,8 @@ void cedrus_device_run(void *priv)
> > 
> >  	run.src = v4l2_m2m_next_src_buf(ctx->fh.m2m_ctx);
> >  	run.dst = v4l2_m2m_next_dst_buf(ctx->fh.m2m_ctx);
> > 
> > +	run.first_slice =
> > +		run.src->vb2_buf.timestamp != run.dst-
>vb2_buf.timestamp;
> 
> Can't we use slice->first_mb_in_slice to determine if a slice is the
> first? I'd expect ->first_mb_in_slice to be 0 (unless we decide to
> support ASO).

I'm not sure if that is always the case, I would have to check the standard. 
Anyway, this method of comparing timestamps was suggested to me a while ago 
when we were discussing details on a way forward for multi-slice decoding. I 
highly doubt someone would decode slices in mixed order (from different frames) 
in same instance.

I can change that in next version if ->first_mb_in_slice == 0 is always true 
for the first slice.

Best regards,
Jernej

> 
> >  	/* Apply request(s) controls if needed. */
> >  	src_req = run.src->vb2_buf.req_obj.req;