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Date:   Sun, 09 Aug 2020 23:11:14 +0200
From:   Jernej Škrabec <jernej.skrabec@...l.net>
To:     Jonas Karlman <jonas@...boo.se>,
        Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Cc:     Ezequiel Garcia <ezequiel@...labora.com>,
        linux-media <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tomasz Figa <tfiga@...omium.org>, kernel@...labora.com,
        Hans Verkuil <hverkuil@...all.nl>,
        Alexandre Courbot <acourbot@...omium.org>,
        Jeffrey Kardatzke <jkardatzke@...omium.org>,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Maxime Ripard <mripard@...nel.org>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Subject: Re: [PATCH v2 03/14] media: uapi: h264: Split prediction weight parameters

Dne nedelja, 09. avgust 2020 ob 15:55:50 CEST je Ezequiel Garcia napisal(a):
> On Sat, 8 Aug 2020 at 18:01, Jonas Karlman <jonas@...boo.se> wrote:
> > On 2020-08-06 17:12, Ezequiel Garcia wrote:
> > > The prediction weight parameters are only required under
> > > certain conditions, which depend on slice header parameters.
> > > 
> > > As specified in section 7.3.3 Slice header syntax, the prediction
> > > weight table is present if:
> > > 
> > > ((weighted_pred_flag && (slice_type == P || slice_type == SP)) || \
> > > (weighted_bipred_idc == 1 && slice_type == B))
> > 
> > Maybe a macro can be added to help check this contition?
> > 
> > Something like this maybe:
> > 
> > #define V4L2_H264_CTRL_PRED_WEIGHTS_REQUIRED(pps, slice) \
> > 
> >         ((((pps)->flags & V4L2_H264_PPS_FLAG_WEIGHTED_PRED) && \
> >         
> >          ((slice)->slice_type == V4L2_H264_SLICE_TYPE_P || \
> >          
> >            (slice)->slice_type == V4L2_H264_SLICE_TYPE_SP)) || \
> >          
> >          ((pps)->weighted_bipred_idc == 1 && \
> >          
> >           (slice)->slice_type == V4L2_H264_SLICE_TYPE_B))
> 
> Yeah, that could make sense.
> 
> Note that the biggest value in having the prediction weight table
> separated is to allow  applications to skip setting this largish control,
> reducing the amount of data that needs to be passed from userspace
> -- especially when not needed :-)
> 
> > > Given its size, it makes sense to move this table to its control,
> > > so applications can avoid passing it if the slice doesn't specify it.
> > > 
> > > Before this change struct v4l2_ctrl_h264_slice_params was 960 bytes.
> > > With this change, it's 188 bytes and struct v4l2_ctrl_h264_pred_weight
> > > is 772 bytes.
> > > 
> > > Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
> > > ---
> > > v2: Fix missing Cedrus changes and mssing control declaration,
> > > 
> > >     as noted by Hans and Jernej.
> > > 
> > > ---
> > > 
> > >  .../media/v4l/ext-ctrls-codec.rst             | 19 ++++++++++++-------
> > >  drivers/media/v4l2-core/v4l2-ctrls.c          |  8 ++++++++
> > >  drivers/staging/media/sunxi/cedrus/cedrus.c   |  7 +++++++
> > >  drivers/staging/media/sunxi/cedrus/cedrus.h   |  1 +
> > >  .../staging/media/sunxi/cedrus/cedrus_dec.c   |  2 ++
> > >  .../staging/media/sunxi/cedrus/cedrus_h264.c  |  6 ++----
> > >  include/media/h264-ctrls.h                    |  5 +++--
> > >  include/media/v4l2-ctrls.h                    |  2 ++
> > >  8 files changed, 37 insertions(+), 13 deletions(-)
> > > 
> > > diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > > b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst index
> > > d1438b1e259f..c36ce5a95fc5 100644
> > > --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > > +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > > @@ -1879,18 +1879,23 @@ enum
> > > v4l2_mpeg_video_h264_hierarchical_coding_type -> > 
> > >        - 0x00000008
> > >        -
> > > 
> > > -``Prediction Weight Table``
> > > +``V4L2_CID_MPEG_VIDEO_H264_PRED_WEIGHTS (struct)``
> > > +    Prediction weight table defined according to :ref:`h264`,
> > > +    section 7.4.3.2 "Prediction Weight Table Semantics".
> > > +    The prediction weight table must be passed by applications
> > > +    under the conditions explained in section 7.3.3 "Slice header
> > > +    syntax".
> > > 
> > > -    The bitstream parameters are defined according to :ref:`h264`,
> > > -    section 7.4.3.2 "Prediction Weight Table Semantics". For further
> > > -    documentation, refer to the above specification, unless there is
> > > -    an explicit comment stating otherwise.
> > > +    .. note::
> > > +
> > > +       This compound control is not yet part of the public kernel API
> > > and
> > > +       it is expected to change.
> > > 
> > > -.. c:type:: v4l2_h264_pred_weight_table
> > > +.. c:type:: v4l2_ctrl_h264_pred_weights
> > > 
> > >  .. cssclass:: longtable
> > > 
> > > -.. flat-table:: struct v4l2_h264_pred_weight_table
> > > +.. flat-table:: struct v4l2_ctrl_h264_pred_weights
> > > 
> > >      :header-rows:  0
> > >      :stub-columns: 0
> > >      :widths:       1 1 2
> > > 
> > > diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c
> > > b/drivers/media/v4l2-core/v4l2-ctrls.c index 3f3fbcd60cc6..76c8dc8fb31c
> > > 100644
> > > --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> > > +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> > > @@ -897,6 +897,7 @@ const char *v4l2_ctrl_get_name(u32 id)
> > > 
> > >       case V4L2_CID_MPEG_VIDEO_H264_DECODE_PARAMS:            return
> > >       "H264 Decode Parameters"; case
> > >       V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE:              return "H264
> > >       Decode Mode"; case V4L2_CID_MPEG_VIDEO_H264_START_CODE:          
> > >           return "H264 Start Code";> > 
> > > +     case V4L2_CID_MPEG_VIDEO_H264_PRED_WEIGHTS:             return
> > > "H264 Prediction Weight Table";> > 
> > >       case V4L2_CID_MPEG_VIDEO_MPEG2_LEVEL:                   return
> > >       "MPEG2 Level"; case V4L2_CID_MPEG_VIDEO_MPEG2_PROFILE:           
> > >            return "MPEG2 Profile"; case
> > >       V4L2_CID_MPEG_VIDEO_MPEG4_I_FRAME_QP:              return "MPEG4
> > >       I-Frame QP Value";> > 
> > > @@ -1412,6 +1413,9 @@ void v4l2_ctrl_fill(u32 id, const char **name,
> > > enum v4l2_ctrl_type *type,> > 
> > >       case V4L2_CID_MPEG_VIDEO_H264_DECODE_PARAMS:
> > >               *type = V4L2_CTRL_TYPE_H264_DECODE_PARAMS;
> > >               break;
> > > 
> > > +     case V4L2_CID_MPEG_VIDEO_H264_PRED_WEIGHTS:
> > > +             *type = V4L2_CTRL_TYPE_H264_PRED_WEIGHTS;
> > > +             break;
> > > 
> > >       case V4L2_CID_MPEG_VIDEO_VP8_FRAME_HEADER:
> > >               *type = V4L2_CTRL_TYPE_VP8_FRAME_HEADER;
> > >               break;
> > > 
> > > @@ -1790,6 +1794,7 @@ static int std_validate_compound(const struct
> > > v4l2_ctrl *ctrl, u32 idx,> > 
> > >       case V4L2_CTRL_TYPE_H264_SPS:
> > >       case V4L2_CTRL_TYPE_H264_PPS:
> > > 
> > >       case V4L2_CTRL_TYPE_H264_SCALING_MATRIX:
> > > +     case V4L2_CTRL_TYPE_H264_PRED_WEIGHTS:
> > >       case V4L2_CTRL_TYPE_H264_SLICE_PARAMS:
> > >       
> > >       case V4L2_CTRL_TYPE_H264_DECODE_PARAMS:
> > >               break;
> > > 
> > > @@ -2553,6 +2558,9 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct
> > > v4l2_ctrl_handler *hdl,> > 
> > >       case V4L2_CTRL_TYPE_H264_DECODE_PARAMS:
> > >               elem_size = sizeof(struct v4l2_ctrl_h264_decode_params);
> > >               break;
> > > 
> > > +     case V4L2_CTRL_TYPE_H264_PRED_WEIGHTS:
> > > +             elem_size = sizeof(struct v4l2_ctrl_h264_pred_weights);
> > > +             break;
> > > 
> > >       case V4L2_CTRL_TYPE_VP8_FRAME_HEADER:
> > >               elem_size = sizeof(struct v4l2_ctrl_vp8_frame_header);
> > >               break;
> > > 
> > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.c
> > > b/drivers/staging/media/sunxi/cedrus/cedrus.c index
> > > bc27f9430eeb..027cdd1be5a0 100644
> > > --- a/drivers/staging/media/sunxi/cedrus/cedrus.c
> > > +++ b/drivers/staging/media/sunxi/cedrus/cedrus.c
> > > @@ -78,6 +78,13 @@ static const struct cedrus_control cedrus_controls[]
> > > = {
> > > 
> > >               .codec          = CEDRUS_CODEC_H264,
> > >               .required       = true,
> > >       
> > >       },
> > > 
> > > +     {
> > > +             .cfg = {
> > > +                     .id     = V4L2_CID_MPEG_VIDEO_H264_PRED_WEIGHTS,
> > > +             },
> > > +             .codec          = CEDRUS_CODEC_H264,
> > > +             .required       = true,
> > 
> > This should probably be false if this control is to be optional as implied
> > by the commit message.
> 
> Well, the control is optional if the driver implements it as optional,
> which Cedrus isn't currently doing :-)

Why do you think so? Prediction weights are filled only when they are 
needed:https://elixir.bootlin.com/linux/latest/source/drivers/staging/media/
sunxi/cedrus/cedrus_h264.c#L370

Best regards,
Jernej

> 
> I have been reluctant to change Cedrus much, since I am not
> testing there. Perhaps we can address this with a follow-up patch,
> adding the macro you suggest and changing the control to optional?
> 
> Speaking of optional controls, note that v4l2 controls are cached
> per-fd (per context). This means for instance, that the active PPS
> and SPS need only be passed to drivers when activated,
> and not on each frame.
> 
> Similarly, another optimization to reduce the amount of
> data passed is to have default scaling matrices in the kernel,
> and allow applications to not pass them, and have the drivers
> fallback to default (default or previously set?) in that case.
> 
> I have tested these things, but haven't posted patches because
> I'm not entirely sure how well-defined and specified this behavior
> currently is. It is something to keep in mind though, as a future
> optimization.
> 
> Thanks!
> Ezequiel
> 
> > Best regards,
> > Jonas
> > 
> > > +     },
> > > 
> > >       {
> > >       
> > >               .cfg = {
> > >               
> > >                       .id     = V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE,
> > > 
> > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.h
> > > b/drivers/staging/media/sunxi/cedrus/cedrus.h index
> > > 96765555ab8a..93c843ae14bb 100644
> > > --- a/drivers/staging/media/sunxi/cedrus/cedrus.h
> > > +++ b/drivers/staging/media/sunxi/cedrus/cedrus.h
> > > @@ -62,6 +62,7 @@ struct cedrus_h264_run {
> > > 
> > >       const struct v4l2_ctrl_h264_scaling_matrix      *scaling_matrix;
> > >       const struct v4l2_ctrl_h264_slice_params        *slice_params;
> > >       const struct v4l2_ctrl_h264_sps                 *sps;
> > > 
> > > +     const struct v4l2_ctrl_h264_pred_weights        *pred_weights;
> > > 
> > >  };
> > >  
> > >  struct cedrus_mpeg2_run {
> > > 
> > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> > > b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c index
> > > 58c48e4fdfe9..6385026d1b6b 100644
> > > --- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> > > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> > > @@ -57,6 +57,8 @@ void cedrus_device_run(void *priv)
> > > 
> > >                       V4L2_CID_MPEG_VIDEO_H264_SLICE_PARAMS);
> > >               
> > >               run.h264.sps = cedrus_find_control_data(ctx,
> > >               
> > >                       V4L2_CID_MPEG_VIDEO_H264_SPS);
> > > 
> > > +             run.h264.pred_weights = cedrus_find_control_data(ctx,
> > > +                     V4L2_CID_MPEG_VIDEO_H264_PRED_WEIGHTS);
> > > 
> > >               break;
> > >       
> > >       case V4L2_PIX_FMT_HEVC_SLICE:
> > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > > b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c index
> > > cce527bbdf86..a9ba78b15907 100644
> > > --- a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
> > > @@ -256,10 +256,8 @@ static void cedrus_write_scaling_lists(struct
> > > cedrus_ctx *ctx,> > 
> > >  static void cedrus_write_pred_weight_table(struct cedrus_ctx *ctx,
> > >  
> > >                                          struct cedrus_run *run)
> > >  
> > >  {
> > > 
> > > -     const struct v4l2_ctrl_h264_slice_params *slice =
> > > -             run->h264.slice_params;
> > > -     const struct v4l2_h264_pred_weight_table *pred_weight =
> > > -             &slice->pred_weight_table;
> > > +     const struct v4l2_ctrl_h264_pred_weights *pred_weight =
> > > +             run->h264.pred_weights;
> > > 
> > >       struct cedrus_dev *dev = ctx->dev;
> > >       int i, j, k;
> > > 
> > > diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
> > > index 4c0bb7f5fb05..54cd9bec0b23 100644
> > > --- a/include/media/h264-ctrls.h
> > > +++ b/include/media/h264-ctrls.h
> > > @@ -36,6 +36,7 @@
> > > 
> > >  #define V4L2_CID_MPEG_VIDEO_H264_DECODE_PARAMS      
> > >  (V4L2_CID_MPEG_BASE+1004) #define V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE
> > >  (V4L2_CID_MPEG_BASE+1005) #define V4L2_CID_MPEG_VIDEO_H264_START_CODE 
> > >  (V4L2_CID_MPEG_BASE+1006)> > 
> > > +#define V4L2_CID_MPEG_VIDEO_H264_PRED_WEIGHTS       
> > > (V4L2_CID_MPEG_BASE+1007)> > 
> > >  /* enum v4l2_ctrl_type type values */
> > >  #define V4L2_CTRL_TYPE_H264_SPS                      0x0110
> > > 
> > > @@ -43,6 +44,7 @@
> > > 
> > >  #define V4L2_CTRL_TYPE_H264_SCALING_MATRIX   0x0112
> > >  #define V4L2_CTRL_TYPE_H264_SLICE_PARAMS     0x0113
> > >  #define V4L2_CTRL_TYPE_H264_DECODE_PARAMS    0x0114
> > > 
> > > +#define V4L2_CTRL_TYPE_H264_PRED_WEIGHTS     0x0115
> > > 
> > >  enum v4l2_mpeg_video_h264_decode_mode {
> > >  
> > >       V4L2_MPEG_VIDEO_H264_DECODE_MODE_SLICE_BASED,
> > > 
> > > @@ -125,7 +127,7 @@ struct v4l2_h264_weight_factors {
> > > 
> > >       __s16 chroma_offset[32][2];
> > >  
> > >  };
> > > 
> > > -struct v4l2_h264_pred_weight_table {
> > > +struct v4l2_ctrl_h264_pred_weights {
> > > 
> > >       __u16 luma_log2_weight_denom;
> > >       __u16 chroma_log2_weight_denom;
> > >       struct v4l2_h264_weight_factors weight_factors[2];
> > > 
> > > @@ -177,7 +179,6 @@ struct v4l2_ctrl_h264_slice_params {
> > > 
> > >       __s32 delta_pic_order_cnt0;
> > >       __s32 delta_pic_order_cnt1;
> > > 
> > > -     struct v4l2_h264_pred_weight_table pred_weight_table;
> > > 
> > >       /* Size in bits of dec_ref_pic_marking() syntax element. */
> > >       __u32 dec_ref_pic_marking_bit_size;
> > >       /* Size in bits of pic order count syntax. */
> > > 
> > > diff --git a/include/media/v4l2-ctrls.h b/include/media/v4l2-ctrls.h
> > > index f40e2cbb21d3..cb25f345e9ad 100644
> > > --- a/include/media/v4l2-ctrls.h
> > > +++ b/include/media/v4l2-ctrls.h
> > > @@ -51,6 +51,7 @@ struct video_device;
> > > 
> > >   * @p_h264_scaling_matrix:   Pointer to a struct
> > >   v4l2_ctrl_h264_scaling_matrix. * @p_h264_slice_params:     Pointer to
> > >   a struct v4l2_ctrl_h264_slice_params. * @p_h264_decode_params:   
> > >   Pointer to a struct v4l2_ctrl_h264_decode_params.> > 
> > > + * @p_h264_pred_weights:     Pointer to a struct
> > > v4l2_ctrl_h264_pred_weights.> > 
> > >   * @p_vp8_frame_header:              Pointer to a VP8 frame header
> > >   structure. * @p_hevc_sps:                      Pointer to an HEVC
> > >   sequence parameter set structure. * @p_hevc_pps:                     
> > >   Pointer to an HEVC picture parameter set structure.> > 
> > > @@ -74,6 +75,7 @@ union v4l2_ctrl_ptr {
> > > 
> > >       struct v4l2_ctrl_h264_scaling_matrix *p_h264_scaling_matrix;
> > >       struct v4l2_ctrl_h264_slice_params *p_h264_slice_params;
> > >       struct v4l2_ctrl_h264_decode_params *p_h264_decode_params;
> > > 
> > > +     struct v4l2_ctrl_h264_pred_weights *p_h264_pred_weights;
> > > 
> > >       struct v4l2_ctrl_vp8_frame_header *p_vp8_frame_header;
> > >       struct v4l2_ctrl_hevc_sps *p_hevc_sps;
> > >       struct v4l2_ctrl_hevc_pps *p_hevc_pps;




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