linux-kernel - Re: [PATCH 2/2] media: cedrus: Allow using the current dst buffer as reference

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Message-ID: <9b8098a9fde4f7645ffe2da263cee038dd823e69.camel@bootlin.com>
Date:   Wed, 09 Jan 2019 15:42:29 +0100
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com
Cc:     Maxime Ripard <maxime.ripard@...tlin.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Chen-Yu Tsai <wens@...e.org>, Randy Li <ayaka@...lik.info>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Alexandre Courbot <acourbot@...omium.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH 2/2] media: cedrus: Allow using the current dst buffer
 as reference

Hi,

On Wed, 2019-01-09 at 15:29 +0100, Hans Verkuil wrote:
> On 01/09/19 15:19, Paul Kocialkowski wrote:
> > It was reported that some cases of interleaved video decoding require
> > using the current destination buffer as a reference. However, this is
> > no longer possible after the move to vb2_find_timestamp because only
> > dequeued and done buffers are considered.
> > 
> > Add a helper in our driver that also considers the current destination
> > buffer before resorting to vb2_find_timestamp and use it in MPEG-2.
> 
> This patch looks good, but can you also add checks to handle the case
> when no buffer with the given timestamp was found? Probably should be done
> in a third patch.
> 
> I suspect the driver will crash if an unknown timestamp is passed on to the
> driver. I would really like to see that corner case fixed.

You're totally right and I think that more generarlly, the current code
flow is rather fragile whenever something wrong happens in our setup()
codec op. I think we should at least have that op return an error code
and properly deal with it when that occurs.

I am planning on making a cleanup series to fix that.

Before using timestamps, reference buffer index validation was done in
std_validate and now it's fully up to the driver. I wonder if it would
be feasible to bring something back in there since all stateless
drivers will face the same issue. The conditions set in
cedrus_reference_index_find seem generic enough for that, but we should
check that std_validate is not called too early, when the queue is in a
different state (and the buffer might not be dequeud or done yet).

What do you think?

Cheers,

Paul

> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > ---
> >  drivers/staging/media/sunxi/cedrus/cedrus_dec.c   | 13 +++++++++++++
> >  drivers/staging/media/sunxi/cedrus/cedrus_dec.h   |  2 ++
> >  drivers/staging/media/sunxi/cedrus/cedrus_mpeg2.c | 10 ++++++----
> >  3 files changed, 21 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> > index 443fb037e1cf..2c295286766c 100644
> > --- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> > @@ -22,6 +22,19 @@
> >  #include "cedrus_dec.h"
> >  #include "cedrus_hw.h"
> >  
> > +int cedrus_reference_index_find(struct vb2_queue *queue,
> > +				struct vb2_buffer *vb2_buf, u64 timestamp)
> > +{
> > +	/*
> > +	 * Allow using the current capture buffer as reference, which can occur
> > +	 * for field-coded pictures.
> > +	 */
> > +	if (vb2_buf->timestamp == timestamp)
> > +		return vb2_buf->index;
> > +	else
> > +		return vb2_find_timestamp(queue, timestamp, 0);
> > +}
> > +
> >  void cedrus_device_run(void *priv)
> >  {
> >  	struct cedrus_ctx *ctx = priv;
> > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.h b/drivers/staging/media/sunxi/cedrus/cedrus_dec.h
> > index d1ae7903677b..8d0fc248220f 100644
> > --- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.h
> > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.h
> > @@ -16,6 +16,8 @@
> >  #ifndef _CEDRUS_DEC_H_
> >  #define _CEDRUS_DEC_H_
> >  
> > +int cedrus_reference_index_find(struct vb2_queue *queue,
> > +				struct vb2_buffer *vb2_buf, u64 timestamp);
> >  void cedrus_device_run(void *priv);
> >  
> >  #endif
> > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_mpeg2.c b/drivers/staging/media/sunxi/cedrus/cedrus_mpeg2.c
> > index cb45fda9aaeb..81c66a8aa1ac 100644
> > --- a/drivers/staging/media/sunxi/cedrus/cedrus_mpeg2.c
> > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_mpeg2.c
> > @@ -10,6 +10,7 @@
> >  #include <media/videobuf2-dma-contig.h>
> >  
> >  #include "cedrus.h"
> > +#include "cedrus_dec.h"
> >  #include "cedrus_hw.h"
> >  #include "cedrus_regs.h"
> >  
> > @@ -159,8 +160,8 @@ static void cedrus_mpeg2_setup(struct cedrus_ctx *ctx, struct cedrus_run *run)
> >  	cedrus_write(dev, VE_DEC_MPEG_PICBOUNDSIZE, reg);
> >  
> >  	/* Forward and backward prediction reference buffers. */
> > -	forward_idx = vb2_find_timestamp(cap_q,
> > -					 slice_params->forward_ref_ts, 0);
> > +	forward_idx = cedrus_reference_index_find(cap_q, &run->dst->vb2_buf,
> > +						  slice_params->forward_ref_ts);
> >  
> >  	fwd_luma_addr = cedrus_dst_buf_addr(ctx, forward_idx, 0);
> >  	fwd_chroma_addr = cedrus_dst_buf_addr(ctx, forward_idx, 1);
> > @@ -168,8 +169,9 @@ static void cedrus_mpeg2_setup(struct cedrus_ctx *ctx, struct cedrus_run *run)
> >  	cedrus_write(dev, VE_DEC_MPEG_FWD_REF_LUMA_ADDR, fwd_luma_addr);
> >  	cedrus_write(dev, VE_DEC_MPEG_FWD_REF_CHROMA_ADDR, fwd_chroma_addr);
> >  
> > -	backward_idx = vb2_find_timestamp(cap_q,
> > -					  slice_params->backward_ref_ts, 0);
> > +	backward_idx = cedrus_reference_index_find(cap_q, &run->dst->vb2_buf,
> > +						   slice_params->backward_ref_ts);
> > +
> >  	bwd_luma_addr = cedrus_dst_buf_addr(ctx, backward_idx, 0);
> >  	bwd_chroma_addr = cedrus_dst_buf_addr(ctx, backward_idx, 1);
> >  
> > 
-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com