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From:   Jernej =?utf-8?B?xaBrcmFiZWM=?= <jernej.skrabec@siol.net>
To:     Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Cc:     Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
        Maxime Ripard <mripard@kernel.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Chen-Yu Tsai <wens@csie.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Greg KH <gregkh@linuxfoundation.org>,
        Jonas Karlman <jonas@kwiboo.se>,
        Nicolas Dufresne <nicolas@ndufresne.ca>,
        linux-media <linux-media@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        devel@driverdev.osuosl.org,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 1/3] media: uapi: h264: update reference lists
Date:   Wed, 08 Jul 2020 17:57:11 +0200
Message-ID: <3602665.eG79kSnugm@jernej-laptop>
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Hi!

Dne sreda, 08. julij 2020 ob 15:28:52 CEST je Ezequiel Garcia napisal(a):
> Hello Jernej,
> 
> I'd like to post a new H264 uAPI cleanup series soon,
> would you mind resending this, or otherwise do you
> mind if I include this patch in the series?

I don't mind at all. Currently my focus was elsewhere...

> 
> See below for a tiny comment.
> 
> On Thu, 4 Jun 2020 at 15:55, Jernej Skrabec <jernej.skrabec@siol.net> wrote:
> > When dealing with with interlaced frames, reference lists must tell if
> > each particular reference is meant for top or bottom field. This info
> > is currently not provided at all in the H264 related controls.
> > 
> > Make reference lists hold a structure which will also hold flags along
> > index into DPB array. Flags will tell if reference is meant for top or
> > bottom field.
> > 
> > Currently the only user of these lists is Cedrus which is just compile
> > fixed here. Actual usage of newly introduced flags will come in
> > following commit.
> > 
> > Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
> > ---
> > 
> >  .../media/v4l/ext-ctrls-codec.rst             | 40 ++++++++++++++++++-
> >  .../staging/media/sunxi/cedrus/cedrus_h264.c  |  6 +--
> >  include/media/h264-ctrls.h                    | 12 +++++-
> >  3 files changed, 51 insertions(+), 7 deletions(-)
> > 
> > diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst index
> > d0d506a444b1..6c36d298db20 100644
> > --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > @@ -1843,10 +1843,10 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type
> > -> 
> >      * - __u32
> >      
> >        - ``slice_group_change_cycle``
> >        -
> > 
> > -    * - __u8
> > +    * - struct :c:type:`v4l2_h264_reference`
> > 
> >        - ``ref_pic_list0[32]``
> >        - Reference picture list after applying the per-slice modifications
> > 
> > -    * - __u8
> > +    * - struct :c:type:`v4l2_h264_reference`
> > 
> >        - ``ref_pic_list1[32]``
> >        - Reference picture list after applying the per-slice modifications
> >      
> >      * - __u32
> > 
> > @@ -1926,6 +1926,42 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type
> > -
> > 
> >        - ``chroma_offset[32][2]``
> >        -
> > 
> > +``Picture Reference``
> > +
> > +.. c:type:: v4l2_h264_reference
> > +
> > +.. cssclass:: longtable
> > +
> > +.. flat-table:: struct v4l2_h264_reference
> > +    :header-rows:  0
> > +    :stub-columns: 0
> > +    :widths:       1 1 2
> > +
> > +    * - __u16
> > +      - ``flags``
> > +      - See :ref:`Picture Reference Flags <h264_reference_flags>`
> > +    * - __u8
> > +      - ``index``
> > +      -
> > +
> > +.. _h264_reference_flags:
> > +
> > +``Picture Reference Flags``
> > +
> > +.. cssclass:: longtable
> > +
> > +.. flat-table::
> > +    :header-rows:  0
> > +    :stub-columns: 0
> > +    :widths:       1 1 2
> > +
> > +    * - ``V4L2_H264_REFERENCE_FLAG_TOP_FIELD``
> > +      - 0x00000001
> > +      -
> > +    * - ``V4L2_H264_REFERENCE_FLAG_BOTTOM_FIELD``
> > +      - 0x00000002
> > +      -
> > +
> > 
> >  ``V4L2_CID_MPEG_VIDEO_H264_DECODE_PARAMS (struct)``
> >  
> >      Specifies the decode parameters (as extracted from the bitstream)
> >      for the associated H264 slice data. This includes the necessary
> > 
> > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c index
> > 54ee2aa423e2..cce527bbdf86 100644
> > --- a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > @@ -166,8 +166,8 @@ static void cedrus_write_frame_list(struct cedrus_ctx
> > *ctx,> 
> >  static void _cedrus_write_ref_list(struct cedrus_ctx *ctx,
> >  
> >                                    struct cedrus_run *run,
> > 
> > -                                  const u8 *ref_list, u8 num_ref,
> > -                                  enum cedrus_h264_sram_off sram)
> > +                                  const struct v4l2_h264_reference
> > *ref_list, +                                  u8 num_ref, enum
> > cedrus_h264_sram_off sram)> 
> >  {
> >  
> >         const struct v4l2_ctrl_h264_decode_params *decode =
> >         run->h264.decode_params; struct vb2_queue *cap_q;
> > 
> > @@ -188,7 +188,7 @@ static void _cedrus_write_ref_list(struct cedrus_ctx
> > *ctx,> 
> >                 int buf_idx;
> >                 u8 dpb_idx;
> > 
> > -               dpb_idx = ref_list[i];
> > +               dpb_idx = ref_list[i].index;
> > 
> >                 dpb = &decode->dpb[dpb_idx];
> >                 
> >                 if (!(dpb->flags & V4L2_H264_DPB_ENTRY_FLAG_ACTIVE))
> > 
> > diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
> > index 080fd1293c42..9b1cbc9bc38e 100644
> > --- a/include/media/h264-ctrls.h
> > +++ b/include/media/h264-ctrls.h
> > @@ -140,6 +140,14 @@ struct v4l2_h264_pred_weight_table {
> > 
> >  #define V4L2_H264_SLICE_FLAG_DIRECT_SPATIAL_MV_PRED    0x04
> >  #define V4L2_H264_SLICE_FLAG_SP_FOR_SWITCH             0x08
> > 
> > +#define V4L2_H264_REFERENCE_FLAG_TOP_FIELD             0x01
> > +#define V4L2_H264_REFERENCE_FLAG_BOTTOM_FIELD          0x02
> > +
> > +struct v4l2_h264_reference {
> > +       __u8 flags;
> > +       __u8 index;
> > +};
> > +
> > 
> >  struct v4l2_ctrl_h264_slice_params {
> >  
> >         /* Size in bytes, including header */
> >         __u32 size;
> > 
> > @@ -182,8 +190,8 @@ struct v4l2_ctrl_h264_slice_params {
> > 
> >          * Entries on each list are indices into
> >          * v4l2_ctrl_h264_decode_params.dpb[].
> >          */
> > 
> > -       __u8 ref_pic_list0[32];
> > -       __u8 ref_pic_list1[32];
> > +       struct v4l2_h264_reference ref_pic_list0[32];
> > +       struct v4l2_h264_reference ref_pic_list1[32];
> 
> Could we use a macro for "32" here? Something like:
> 
> #define V4L2_H264_REF_PIC_LIST_LEN (V4L2_H264_NUM_DPB_ENTRIES * 2).
> 
> Does it make sense to add a comment as well?
> 
> I was thinking something along these lines:
> 
> """
> Pictures in the DPB can be a frame, a complementary field pair or a
> single field.

To be honest, I don't know if user has a free choice to select same or 
different destination (capture) buffer for another field. I never tested it and 
I'm not sure how to test it with ffmpeg. HW deinterlacing cores on Allwinner 
SoCs support only interleaved fields as a input, that's why I never though 
about separate fields.

Best regards,
Jernej

> Therefore, reference pictures lists need twice as much entries, so it
> can reference
> either field of a field pair.
> """
> 
> While it doesn't replace proper H264 specification reading,
> it would add some clarity.
> 
> Thanks,
> Ezequiel