linux-kernel - Re: [PATCH v5 04/11] media: uapi: h264: Add the concept of start code

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Date:   Wed, 14 Aug 2019 13:49:28 +0200
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Ezequiel Garcia <ezequiel@...labora.com>,
        linux-media@...r.kernel.org, kernel@...labora.com,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Tomasz Figa <tfiga@...omium.org>,
        linux-rockchip@...ts.infradead.org,
        Heiko Stuebner <heiko@...ech.de>,
        Jonas Karlman <jonas@...boo.se>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        fbuergisser@...omium.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 04/11] media: uapi: h264: Add the concept of start code

Hi,

On Wed 14 Aug 19, 10:11, Hans Verkuil wrote:
> On 8/12/19 9:35 PM, Ezequiel Garcia wrote:
> > Stateless decoders have different expectations about the
> > start code that is prepended on H264 slices. Add a
> > menu control to express the supported start code types
> > (including no start code).
> > 
> > Drivers are allowed to support only one start code type,
> > but they can support both too.
> > 
> > Note that this is independent of the H264 decoding mode,
> > which specifies the granularity of the decoding operations.
> > Either in frame-based or slice-based mode, this new control
> > will allow to define the start code expected on H264 slices.
> > 
> > Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
> > Tested-by: Philipp Zabel <p.zabel@...gutronix.de>
> > ---
> > Changes in v5:
> > * Improve specification as suggested by Hans.
> > Changes in v4:
> > * New patch.
> > ---
> >  .../media/uapi/v4l/ext-ctrls-codec.rst        | 33 +++++++++++++++++++
> >  .../media/uapi/v4l/pixfmt-compressed.rst      |  3 +-
> >  drivers/media/v4l2-core/v4l2-ctrls.c          |  9 +++++
> >  include/media/h264-ctrls.h                    |  6 ++++
> >  4 files changed, 50 insertions(+), 1 deletion(-)
> > 
> 
> <snip>
> 
> > diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
> > index e6c510877f67..31555c99f64a 100644
> > --- a/include/media/h264-ctrls.h
> > +++ b/include/media/h264-ctrls.h
> > @@ -27,6 +27,7 @@
> >  #define V4L2_CID_MPEG_VIDEO_H264_SLICE_PARAMS	(V4L2_CID_MPEG_BASE+1003)
> >  #define V4L2_CID_MPEG_VIDEO_H264_DECODE_PARAMS	(V4L2_CID_MPEG_BASE+1004)
> >  #define V4L2_CID_MPEG_VIDEO_H264_DECODING_MODE	(V4L2_CID_MPEG_BASE+1005)
> > +#define V4L2_CID_MPEG_VIDEO_H264_STARTCODE	(V4L2_CID_MPEG_BASE+1006)
> 
> I almost forgot: can you change this to _START_CODE? Since it is two words?

Agreed, I like it better this way too.

> Thanks!
> 
> 	Hans
> 
> >  
> >  /* enum v4l2_ctrl_type type values */
> >  #define V4L2_CTRL_TYPE_H264_SPS			0x0110
> > @@ -41,6 +42,11 @@ enum v4l2_mpeg_video_h264_decoding_mode {
> >  	V4L2_MPEG_VIDEO_H264_FRAME_BASED_DECODING,
> >  };
> >  
> > +enum v4l2_mpeg_video_h264_start_code {
> > +	V4L2_MPEG_VIDEO_H264_NO_STARTCODE,
> > +	V4L2_MPEG_VIDEO_H264_ANNEX_B_STARTCODE,

Could we apply the same START_CODE renaming here too?

I was also thinking that it would be slightly more readable put like this,
with START_CODE as a prefix since it's common to both options and the name of
the enum:

- V4L2_MPEG_VIDEO_H264_START_CODE_NONE
- V4L2_MPEG_VIDEO_H264_START_CODE_ANNEX_B

What do you think?

Cheers,

Paul

> > +};
> > +
> >  #define V4L2_H264_SPS_CONSTRAINT_SET0_FLAG			0x01
> >  #define V4L2_H264_SPS_CONSTRAINT_SET1_FLAG			0x02
> >  #define V4L2_H264_SPS_CONSTRAINT_SET2_FLAG			0x04
> > 
> 

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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