linux-kernel - Re: [PATCH v3 2/3] media: hantro: Support color conversion via post-processing

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Date:   Thu, 05 Dec 2019 15:46:26 +0100
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Ezequiel Garcia <ezequiel@...labora.com>,
        linux-media@...r.kernel.org
Cc:     kernel@...labora.com, Tomasz Figa <tfiga@...omium.org>,
        linux-rockchip@...ts.infradead.org,
        Heiko Stuebner <heiko@...ech.de>,
        Jonas Karlman <jonas@...boo.se>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Chris Healy <cphealy@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/3] media: hantro: Support color conversion via
 post-processing

On Thu, 2019-12-05 at 11:33 -0300, Ezequiel Garcia wrote:
> Hello Philipp,
> 
> On Fri, 2019-11-15 at 12:44 -0300, Ezequiel Garcia wrote:
> > Hello Philipp,
> > 
> > Thanks for reviewing.
> > 
> > On Thu, 2019-11-14 at 10:48 +0100, Philipp Zabel wrote:
> > > Hi Ezequiel,
> > > 
> > > On Wed, 2019-11-13 at 14:56 -0300, Ezequiel Garcia wrote:
> > > > The Hantro G1 decoder is able to enable a post-processor
> > > > on the decoding pipeline, which can be used to perform
> > > > scaling and color conversion.
> > > > 
> > > > The post-processor is integrated to the decoder, and it's
> > > > possible to use it in a way that is completely transparent
> > > > to the user.
> > > > 
> > > > This commit enables color conversion via post-processing,
> > > > which means the driver now exposes YUV packed, in addition to NV12.
> > > > 
> > > > Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
> > > > ---
> > > >  drivers/staging/media/hantro/Makefile         |   1 +
> > > >  drivers/staging/media/hantro/hantro.h         |  64 +++++++-
> > > >  drivers/staging/media/hantro/hantro_drv.c     |   8 +-
> > > >  .../staging/media/hantro/hantro_g1_h264_dec.c |   2 +-
> > > >  .../media/hantro/hantro_g1_mpeg2_dec.c        |   2 +-
> > > >  drivers/staging/media/hantro/hantro_g1_regs.h |  53 +++++++
> > > >  .../staging/media/hantro/hantro_g1_vp8_dec.c  |   2 +-
> > > >  drivers/staging/media/hantro/hantro_h264.c    |   6 +-
> > > >  drivers/staging/media/hantro/hantro_hw.h      |  13 ++
> > > >  .../staging/media/hantro/hantro_postproc.c    | 141 ++++++++++++++++++
> > > >  drivers/staging/media/hantro/hantro_v4l2.c    |  52 ++++++-
> > > >  drivers/staging/media/hantro/rk3288_vpu_hw.c  |  10 ++
> > > >  12 files changed, 343 insertions(+), 11 deletions(-)
> > > >  create mode 100644 drivers/staging/media/hantro/hantro_postproc.c
> > > > 
> > > > 
> [..]
> > > >  			pix_mp->plane_fmt[0].sizeimage +=
> > > >  				128 * DIV_ROUND_UP(pix_mp->width, 16) *
> > > >  				      DIV_ROUND_UP(pix_mp->height, 16);
> > > > @@ -611,10 +643,23 @@ static int hantro_start_streaming(struct vb2_queue *q, unsigned int count)
> > > >  
> > > >  		vpu_debug(4, "Codec mode = %d\n", codec_mode);
> > > >  		ctx->codec_ops = &ctx->dev->variant->codec_ops[codec_mode];
> > > > -		if (ctx->codec_ops->init)
> > > > +		if (ctx->codec_ops->init) {
> > > >  			ret = ctx->codec_ops->init(ctx);
> > > > +			if (ret)
> > > > +				return ret;
> > > > +		}
> > > > +
> > > > +		if (hantro_needs_postproc(ctx)) {
> > > > +			ret = hantro_postproc_alloc(ctx);
> > > 
> > > Why is this done in start_streaming? Wouldn't capture side REQBUFS be a
> > > better place for this?
> > > 
> > 
> > Yes, makes sense as well.
> > 
> 
> This didn't work so well, so I have decided to leave it as-is in the
> just submitted v4 series.
> 
> The vb2 framework provides two mechanism for drivers to allocate
> buffers, REQBUFS and CREATEBUFS, so the bounce buffer allocation
> has to be hooked on both of them.

That is a good point, now that we don't allocate VB2_MAX_FRAME bounce
buffers at start_streaming time anymore, what happens if additional
capture buffers are created with CREATEBUFS while streaming?

> Also, REQBUFS and CREATEBUFS can be called multiple times
> to grow/shrink the vb2_queue, so the driver has to check
> if the bounce buffers were already created or not.
> 
> Not a big deal, but I felt the implementation ended up being
> too nasty for my taste.
> 
> If fragmentation turns out to be an issue and we want to avoid
> allocating and destroying in start and stop (STREAMOFF, STREAMON),
> we can revisit this.

regards
Philipp