Re: [PATCH v6 03/11] media: uapi: h264: Add the concept of decoding mode

[Hans Verkuil <hverkuil@xs4all.nl>]

On 8/14/19 9:59 PM, Ezequiel Garcia wrote:
> From: Boris Brezillon <boris.brezillon@collabora.com>
> 
> Some stateless decoders don't support per-slice decoding granularity
> (or at least not in a way that would make them efficient or easy to use).
> 
> Expose a menu to control the supported decoding modes. Drivers are
> allowed to support only one decoding but they can support both too.

The commit message doesn't say anything about the start_byte_offset
addition and the num_slices documentation improvement. It probably
should.

See more comments below:

> 
> Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
> ---
> Changes in v6:
> * Fix spec, specifiying the decode-mode pixelformat modifier
>   needs to be set once, as suggested by Hans.
> * Rename, as suggested by Paul.
> Changes in v5:
> * Improve specification as suggested by Hans.
> Changes in v4:
> * Typos/rewording fixes
> Changes in v3:
> * s/per-{slice,frame} decoding/{slice,frame}-based decoding/
> * Add Paul's R-b
> Changes in v2:
> * Allow decoding multiple slices in per-slice decoding mode
> * Minor doc improvement/fixes
> ---
>  .../media/uapi/v4l/ext-ctrls-codec.rst        | 47 ++++++++++++++++++-
>  .../media/uapi/v4l/pixfmt-compressed.rst      |  6 ++-
>  drivers/media/v4l2-core/v4l2-ctrls.c          |  9 ++++
>  include/media/h264-ctrls.h                    | 10 ++++
>  4 files changed, 69 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> index c5f39dd50043..623b34f61b32 100644
> --- a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> @@ -1747,6 +1747,11 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>      * - __u32
>        - ``size``
>        -
> +    * - __u32
> +      - ``start_byte_offset``
> +        Offset (in bytes) from the beginning of the OUTPUT buffer to the start
> +        of the slice. If the slice starts with a start code, then this is the
> +        offset to such start code.

This should mention that it should be set to 0 for SLICE_BASED decoding mode.

>      * - __u32
>        - ``header_bit_size``
>        -
> @@ -1930,7 +1935,10 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>        -
>      * - __u16
>        - ``num_slices``
> -      - Number of slices needed to decode the current frame
> +      - Number of slices needed to decode the current frame/field. When
> +        operating in slice-based decoding mode (see
> +        :c:type:`v4l2_mpeg_video_h264_decode_mode`), this field
> +        should always be set to one.
>      * - __u16
>        - ``nal_ref_idc``
>        - NAL reference ID value coming from the NAL Unit header
> @@ -2021,6 +2029,43 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>        - 0x00000004
>        - The DPB entry is a long term reference frame
>  
> +``V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE (enum)``
> +    Specifies the decoding mode to use. Currently exposes slice-based and
> +    frame-based decoding but new modes might be added later on.
> +    This control is used as a modifier for V4L2_PIX_FMT_H264_SLICE
> +    pixel format. Applications that support V4L2_PIX_FMT_H264_SLICE
> +    are required to set this control in order to specify the decoding mode
> +    that is expected for the buffer.
> +    Drivers may expose a single or multiple decoding modes, depending
> +    on what they can support.
> +
> +    .. note::
> +
> +       This menu control is not yet part of the public kernel API and
> +       it is expected to change.
> +
> +.. c:type:: v4l2_mpeg_video_h264_decode_mode
> +
> +.. cssclass:: longtable
> +
> +.. flat-table::
> +    :header-rows:  0
> +    :stub-columns: 0
> +    :widths:       1 1 2
> +
> +    * - ``V4L2_MPEG_VIDEO_H264_DECODE_MODE_SLICE_BASED``
> +      - 0
> +      - Decoding is done at the slice granularity.
> +        v4l2_ctrl_h264_decode_params->num_slices should be set to 1.

And start_byte_offset should be set to 0.

> +        The OUTPUT buffer must contain a single slice.
> +    * - ``V4L2_MPEG_VIDEO_H264_DECODE_MODE_FRAME_BASED``
> +      - 1
> +      - Decoding is done at the frame granularity.
> +        v4l2_ctrl_h264_decode_params->num_slices should be set to the number of
> +        slices forming a frame.

And start_byte_offset should be filled in accordingly for each slice.

Regards,

	Hans

> +        The OUTPUT buffer must contain all slices needed to decode the
> +        frame. The OUTPUT buffer must also contain both fields.
> +
>  .. _v4l2-mpeg-mpeg2:
>  
>  ``V4L2_CID_MPEG_VIDEO_MPEG2_SLICE_PARAMS (struct)``
> diff --git a/Documentation/media/uapi/v4l/pixfmt-compressed.rst b/Documentation/media/uapi/v4l/pixfmt-compressed.rst
> index 9b65473a2288..d666eb51741a 100644
> --- a/Documentation/media/uapi/v4l/pixfmt-compressed.rst
> +++ b/Documentation/media/uapi/v4l/pixfmt-compressed.rst
> @@ -60,8 +60,10 @@ Compressed Formats
>  	extracted from the H264 bitstream.  This format is adapted for
>  	stateless video decoders that implement an H264 pipeline
>  	(using the :ref:`mem2mem` and :ref:`media-request-api`).
> -	Metadata associated with the frame to decode are required to
> -	be passed through the ``V4L2_CID_MPEG_VIDEO_H264_SPS``,
> +	This pixelformat has a modifier that must be set at least once
> +	through the ``V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE`` control.
> +	In addition, metadata associated with the frame to decode are
> +	required to be passed through the ``V4L2_CID_MPEG_VIDEO_H264_SPS``,
>  	``V4L2_CID_MPEG_VIDEO_H264_PPS``,
>  	``V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX``,
>  	``V4L2_CID_MPEG_VIDEO_H264_SLICE_PARAMS`` and
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> index cd1ae016706f..2c67f9fc4d5b 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> @@ -402,6 +402,11 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
>  		"Explicit",
>  		NULL,
>  	};
> +	static const char * const h264_decode_mode[] = {
> +		"Slice-Based",
> +		"Frame-Based",
> +		NULL,
> +	};
>  	static const char * const mpeg_mpeg2_level[] = {
>  		"Low",
>  		"Main",
> @@ -633,6 +638,8 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
>  		return h264_fp_arrangement_type;
>  	case V4L2_CID_MPEG_VIDEO_H264_FMO_MAP_TYPE:
>  		return h264_fmo_map_type;
> +	case V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE:
> +		return h264_decode_mode;
>  	case V4L2_CID_MPEG_VIDEO_MPEG2_LEVEL:
>  		return mpeg_mpeg2_level;
>  	case V4L2_CID_MPEG_VIDEO_MPEG2_PROFILE:
> @@ -852,6 +859,7 @@ const char *v4l2_ctrl_get_name(u32 id)
>  	case V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX:		return "H264 Scaling Matrix";
>  	case V4L2_CID_MPEG_VIDEO_H264_SLICE_PARAMS:		return "H264 Slice Parameters";
>  	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_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";
> @@ -1220,6 +1228,7 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
>  	case V4L2_CID_MPEG_VIDEO_H264_VUI_SAR_IDC:
>  	case V4L2_CID_MPEG_VIDEO_H264_SEI_FP_ARRANGEMENT_TYPE:
>  	case V4L2_CID_MPEG_VIDEO_H264_FMO_MAP_TYPE:
> +	case V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE:
>  	case V4L2_CID_MPEG_VIDEO_MPEG2_LEVEL:
>  	case V4L2_CID_MPEG_VIDEO_MPEG2_PROFILE:
>  	case V4L2_CID_MPEG_VIDEO_MPEG4_LEVEL:
> diff --git a/include/media/h264-ctrls.h b/include/media/h264-ctrls.h
> index 6160a69c0143..928c48c57282 100644
> --- a/include/media/h264-ctrls.h
> +++ b/include/media/h264-ctrls.h
> @@ -26,6 +26,7 @@
>  #define V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX	(V4L2_CID_MPEG_BASE+1002)
>  #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_DECODE_MODE	(V4L2_CID_MPEG_BASE+1005)
>  
>  /* enum v4l2_ctrl_type type values */
>  #define V4L2_CTRL_TYPE_H264_SPS			0x0110
> @@ -34,6 +35,11 @@
>  #define V4L2_CTRL_TYPE_H264_SLICE_PARAMS	0x0113
>  #define V4L2_CTRL_TYPE_H264_DECODE_PARAMS	0x0114
>  
> +enum v4l2_mpeg_video_h264_decode_mode {
> +	V4L2_MPEG_VIDEO_H264_DECODE_MODE_SLICE_BASED,
> +	V4L2_MPEG_VIDEO_H264_DECODE_MODE_FRAME_BASED,
> +};
> +
>  #define V4L2_H264_SPS_CONSTRAINT_SET0_FLAG			0x01
>  #define V4L2_H264_SPS_CONSTRAINT_SET1_FLAG			0x02
>  #define V4L2_H264_SPS_CONSTRAINT_SET2_FLAG			0x04
> @@ -125,6 +131,10 @@ struct v4l2_h264_pred_weight_table {
>  struct v4l2_ctrl_h264_slice_params {
>  	/* Size in bytes, including header */
>  	__u32 size;
> +
> +	/* Offset in bytes to the start of slice in the OUTPUT buffer. */
> +	__u32 start_byte_offset;
> +
>  	/* Offset in bits to slice_data() from the beginning of this slice. */
>  	__u32 header_bit_size;
>  
>