linux-kernel - Re: [PATCH v7 02/11] media: uapi: h264: Rename pixel format

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Date:   Mon, 19 Aug 2019 14:41:10 +0200
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Ezequiel Garcia <ezequiel@...labora.com>
Cc:     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 v7 02/11] media: uapi: h264: Rename pixel format

Hi,

On Fri 16 Aug 19, 13:01, Ezequiel Garcia wrote:
> The V4L2_PIX_FMT_H264_SLICE_RAW name was originally suggested
> because the pixel format would represent H264 slices without any
> start code.
> 
> However, as we will now introduce a start code menu control,
> give the pixel format a more meaningful name, while it's
> still early enough to do so.

I definitely agree that SLICE_RAW is not the suffix we are looking for, but I'm
not sure that _SLICE is self-describing given that we can operate either
per-frame or per-slice, and _SLICE sort of implies the latter. Also, VP8 uses
_FRAME to clearly indicate that it operates per-frame.

In addition, the _SLICE suffix is used by MPEG-2 in the stable API. Since we
certainly want MPEG-2 to allow per-slice and per-frame decoding as well as
H.264 and that the _SLICE format is specified to be the broken "concatenated
slices" that cedrus expects, we probably want to use another suffix. This way,
we could deprecated MPEG2_SLICE and introduce a new format for MPEG-2 that would
have consistent naming with the other mpeg formats.

One suggestion I had was to call it H264_PARSED (and apply this to MPEG-2 and
HEVC when similar controls to H.264 are set in place for them). I think Hans had
another suggestion for the name but I don't recall what it was at this point.

Either way, if this has to be some debate, we could perhaps take it off your
series and stay with SLICE_RAW for now, as long as we do rename it before making
the API stable.

What do you think?

Cheers,

Paul

> Signed-off-by: Ezequiel Garcia <ezequiel@...labora.com>
> Tested-by: Philipp Zabel <p.zabel@...gutronix.de>
> ---
> Changes in v7:
> * None.
> Changes in v6:
> * None.
> Changes in v5:
> * None.
> Changes in v4:
> * New patch.
> ---
>  Documentation/media/uapi/v4l/pixfmt-compressed.rst | 4 ++--
>  drivers/media/v4l2-core/v4l2-ioctl.c               | 2 +-
>  drivers/staging/media/sunxi/cedrus/cedrus_dec.c    | 2 +-
>  drivers/staging/media/sunxi/cedrus/cedrus_video.c  | 6 +++---
>  include/media/h264-ctrls.h                         | 2 +-
>  5 files changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/media/uapi/v4l/pixfmt-compressed.rst b/Documentation/media/uapi/v4l/pixfmt-compressed.rst
> index f52a7b67023d..9b65473a2288 100644
> --- a/Documentation/media/uapi/v4l/pixfmt-compressed.rst
> +++ b/Documentation/media/uapi/v4l/pixfmt-compressed.rst
> @@ -52,9 +52,9 @@ Compressed Formats
>        - ``V4L2_PIX_FMT_H264_MVC``
>        - 'M264'
>        - H264 MVC video elementary stream.
> -    * .. _V4L2-PIX-FMT-H264-SLICE-RAW:
> +    * .. _V4L2-PIX-FMT-H264-SLICE:
>  
> -      - ``V4L2_PIX_FMT_H264_SLICE_RAW``
> +      - ``V4L2_PIX_FMT_H264_SLICE``
>        - 'S264'
>        - H264 parsed slice data, without the start code and as
>  	extracted from the H264 bitstream.  This format is adapted for
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index bb5b4926538a..39f10621c91b 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -1343,7 +1343,7 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
>  		case V4L2_PIX_FMT_H264:		descr = "H.264"; break;
>  		case V4L2_PIX_FMT_H264_NO_SC:	descr = "H.264 (No Start Codes)"; break;
>  		case V4L2_PIX_FMT_H264_MVC:	descr = "H.264 MVC"; break;
> -		case V4L2_PIX_FMT_H264_SLICE_RAW:	descr = "H.264 Parsed Slice Data"; break;
> +		case V4L2_PIX_FMT_H264_SLICE:	descr = "H.264 Parsed Slice Data"; break;
>  		case V4L2_PIX_FMT_H263:		descr = "H.263"; break;
>  		case V4L2_PIX_FMT_MPEG1:	descr = "MPEG-1 ES"; break;
>  		case V4L2_PIX_FMT_MPEG2:	descr = "MPEG-2 ES"; break;
> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> index bdad87eb9d79..56ca4c9ad01c 100644
> --- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> +++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
> @@ -46,7 +46,7 @@ void cedrus_device_run(void *priv)
>  			V4L2_CID_MPEG_VIDEO_MPEG2_QUANTIZATION);
>  		break;
>  
> -	case V4L2_PIX_FMT_H264_SLICE_RAW:
> +	case V4L2_PIX_FMT_H264_SLICE:
>  		run.h264.decode_params = cedrus_find_control_data(ctx,
>  			V4L2_CID_MPEG_VIDEO_H264_DECODE_PARAMS);
>  		run.h264.pps = cedrus_find_control_data(ctx,
> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_video.c b/drivers/staging/media/sunxi/cedrus/cedrus_video.c
> index 681dfe3367a6..eeee3efd247b 100644
> --- a/drivers/staging/media/sunxi/cedrus/cedrus_video.c
> +++ b/drivers/staging/media/sunxi/cedrus/cedrus_video.c
> @@ -38,7 +38,7 @@ static struct cedrus_format cedrus_formats[] = {
>  		.directions	= CEDRUS_DECODE_SRC,
>  	},
>  	{
> -		.pixelformat	= V4L2_PIX_FMT_H264_SLICE_RAW,
> +		.pixelformat	= V4L2_PIX_FMT_H264_SLICE,
>  		.directions	= CEDRUS_DECODE_SRC,
>  	},
>  	{
> @@ -104,7 +104,7 @@ static void cedrus_prepare_format(struct v4l2_pix_format *pix_fmt)
>  
>  	switch (pix_fmt->pixelformat) {
>  	case V4L2_PIX_FMT_MPEG2_SLICE:
> -	case V4L2_PIX_FMT_H264_SLICE_RAW:
> +	case V4L2_PIX_FMT_H264_SLICE:
>  		/* Zero bytes per line for encoded source. */
>  		bytesperline = 0;
>  
> @@ -449,7 +449,7 @@ static int cedrus_start_streaming(struct vb2_queue *vq, unsigned int count)
>  		ctx->current_codec = CEDRUS_CODEC_MPEG2;
>  		break;
>  
> -	case V4L2_PIX_FMT_H264_SLICE_RAW:
> +	case V4L2_PIX_FMT_H264_SLICE:
>  		ctx->current_codec = CEDRUS_CODEC_H264;
>  		break;
>  
> diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
> index e1404d78d6ff..6160a69c0143 100644
> --- a/include/media/h264-ctrls.h
> +++ b/include/media/h264-ctrls.h
> @@ -14,7 +14,7 @@
>  #include <linux/videodev2.h>
>  
>  /* Our pixel format isn't stable at the moment */
> -#define V4L2_PIX_FMT_H264_SLICE_RAW v4l2_fourcc('S', '2', '6', '4') /* H264 parsed slices */
> +#define V4L2_PIX_FMT_H264_SLICE v4l2_fourcc('S', '2', '6', '4') /* H264 parsed slices */
>  
>  /*
>   * This is put insanely high to avoid conflicting with controls that
> -- 
> 2.22.0
> 

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

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