linux-kernel - Re: [RFC 07/12] media: uapi: h264: Add DPB entry field reference flags

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Message-ID: <20200710101333.05077f18@collabora.com>
Date:   Fri, 10 Jul 2020 10:13:33 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Ezequiel Garcia <ezequiel@...labora.com>
Cc:     Jonas Karlman <jonas@...boo.se>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-rockchip@...ts.infradead.org" 
        <linux-rockchip@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 07/12] media: uapi: h264: Add DPB entry field reference
 flags

On Fri, 10 Jul 2020 01:21:07 -0300
Ezequiel Garcia <ezequiel@...labora.com> wrote:

> Hello Jonas,
> 
> In the context of the uAPI cleanup,
> I'm revisiting this patch.
> 
> On Sun, 2019-09-01 at 12:45 +0000, Jonas Karlman wrote:
> > Add DPB entry flags to help indicate when a reference frame is a field picture
> > and how the DPB entry is referenced, top or bottom field or full frame.
> > 
> > Signed-off-by: Jonas Karlman <jonas@...boo.se>
> > ---
> >  Documentation/media/uapi/v4l/ext-ctrls-codec.rst | 12 ++++++++++++
> >  include/media/h264-ctrls.h                       |  4 ++++
> >  2 files changed, 16 insertions(+)
> > 
> > diff --git a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> > index bc5dd8e76567..eb6c32668ad7 100644
> > --- a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> > +++ b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> > @@ -2022,6 +2022,18 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
> >      * - ``V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM``
> >        - 0x00000004
> >        - The DPB entry is a long term reference frame
> > +    * - ``V4L2_H264_DPB_ENTRY_FLAG_FIELD_PICTURE``
> > +      - 0x00000008
> > +      - The DPB entry is a field picture
> > +    * - ``V4L2_H264_DPB_ENTRY_FLAG_REF_TOP``
> > +      - 0x00000010
> > +      - The DPB entry is a top field reference
> > +    * - ``V4L2_H264_DPB_ENTRY_FLAG_REF_BOTTOM``
> > +      - 0x00000020
> > +      - The DPB entry is a bottom field reference
> > +    * - ``V4L2_H264_DPB_ENTRY_FLAG_REF_FRAME``
> > +      - 0x00000030
> > +      - The DPB entry is a reference frame
> >  
> >  ``V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE (enum)``
> >      Specifies the decoding mode to use. Currently exposes slice-based and
> > diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
> > index e877bf1d537c..76020ebd1e6c 100644
> > --- a/include/media/h264-ctrls.h
> > +++ b/include/media/h264-ctrls.h
> > @@ -185,6 +185,10 @@ struct v4l2_ctrl_h264_slice_params {
> >  #define V4L2_H264_DPB_ENTRY_FLAG_VALID		0x01
> >  #define V4L2_H264_DPB_ENTRY_FLAG_ACTIVE		0x02
> >  #define V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM	0x04
> > +#define V4L2_H264_DPB_ENTRY_FLAG_FIELD_PICTURE	0x08
> > +#define V4L2_H264_DPB_ENTRY_FLAG_REF_TOP	0x10
> > +#define V4L2_H264_DPB_ENTRY_FLAG_REF_BOTTOM	0x20
> > +#define V4L2_H264_DPB_ENTRY_FLAG_REF_FRAME	0x30
> >    
> 
> I've been going thru the H264 spec and I'm unsure,
> are all these flags semantically needed?
> 
> For instance, if one of REF_BOTTOM or REF_TOP (or both)
> are set, doesn't that indicate it's a field picture?
> 
> Or conversely, if neither REF_BOTTOM or REF_TOP are set,
> then it's a frame picture?

I think that's what I was trying to do here [1]

[1]https://patchwork.kernel.org/patch/11392095/