Re: [PATCH v11 11/17] media: uapi: Add V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSETS control

Ezequiel Garcia
2022-07-08T10:42:16Z

Hi Benjamin, Jernej,

On Wed, Jul 06, 2022 at 11:37:57AM +0200, Benjamin Gaignard wrote:
> The number of 'entry point offset' can be very variable.
> Instead of using a large static array define a v4l2 dynamic array
> of U32 (V4L2_CTRL_TYPE_U32).
> The number of entry point offsets is reported by the elems field
> and in struct v4l2_ctrl_hevc_slice_params.num_entry_point_offsets
> field.
>
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
> Acked-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
> Tested-by: Jernej Skrabec <jernej.skrabec@gmail.com>
> ---
> version 11:
> - Be more verbose about num_entry_point_offsets field usage.
>
> .../userspace-api/media/v4l/ext-ctrls-codec.rst | 15 +++++++++++++++
> drivers/media/v4l2-core/v4l2-ctrls-defs.c | 5 +++++
> include/media/hevc-ctrls.h | 5 ++++-
> 3 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> index c2e0adece613..59e751c38d06 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> @@ -3010,6 +3010,13 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
> * - __u32
> - ``data_bit_offset``
> - Offset (in bits) to the video data in the current slice data.
> + * - __u32
> + - ``num_entry_point_offsets``
> + - Specifies the number of entry point offset syntax elements in the slice header.

Given this field really matches the syntax element (thanks for the
clarification), I would suggest keeping it simpler,
maybe something along these lines:

""
Specifies the number of entry point offset syntax elements in the slice header.
When the driver supports it, the ``V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSETS``
must be set.
""

> + This field must be set even if V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSETS
> + control isn't used. Additionally, if entry point offsets control is needed
> + and if submitting multiple slices at once, length of entry point offsets
> + array must be sum of num_entry_point_offsets of all slices in that job.

> * - __u8
> - ``nal_unit_type``
> - Specifies the coding type of the slice (B, P or I).
> @@ -3150,6 +3157,14 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
>
> \normalsize
>
> +``V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSETS (integer)``
> + Specifies entry point offsets in bytes.
> + This control is a dynamically sized array. The number of entry point
> + offsets is reported by the ``elems`` field.
> + This bitstream parameter is defined according to :ref:`hevc`.
> + They are described in section 7.4.7.1 "General slice segment header
> + semantics" of the specification.
> +

I would add Jernej's clarification about the length of the control
here, where the control is documented.

""
This control is a dynamically sized array. The number of entry point
offsets is reported by the ``elems`` field.
This bitstream parameter is defined according to :ref:`hevc`.
They are described in section 7.4.7.1 "General slice segment header
semantics" of the specification.
When multiple slices are submitted in a request, the length
of this array must be the sum of num_entry_point_offsets
of all the slices in the request.
""

Hopefully this is clearer to application developers?

Thanks!
Ezequiel

> ``V4L2_CID_STATELESS_HEVC_SCALING_MATRIX (struct)``
> Specifies the HEVC scaling matrix parameters used for the scaling process
> for transform coefficients.
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-defs.c b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> index d594efbcbb93..e22921e7ea61 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> @@ -1188,6 +1188,7 @@ const char *v4l2_ctrl_get_name(u32 id)
> case V4L2_CID_STATELESS_HEVC_DECODE_PARAMS: return "HEVC Decode Parameters";
> case V4L2_CID_STATELESS_HEVC_DECODE_MODE: return "HEVC Decode Mode";
> case V4L2_CID_STATELESS_HEVC_START_CODE: return "HEVC Start Code";
> + case V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSETS: return "HEVC Entry Point Offsets";
>
> /* Colorimetry controls */
> /* Keep the order of the 'case's the same as in v4l2-controls.h! */
> @@ -1518,6 +1519,10 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
> case V4L2_CID_STATELESS_HEVC_DECODE_PARAMS:
> *type = V4L2_CTRL_TYPE_HEVC_DECODE_PARAMS;
> break;
> + case V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSETS:
> + *type = V4L2_CTRL_TYPE_U32;
> + *flags |= V4L2_CTRL_FLAG_DYNAMIC_ARRAY;
> + break;
> case V4L2_CID_STATELESS_VP9_COMPRESSED_HDR:
> *type = V4L2_CTRL_TYPE_VP9_COMPRESSED_HDR;
> break;
> diff --git a/include/media/hevc-ctrls.h b/include/media/hevc-ctrls.h
> index a372c184689e..3a6601a46ced 100644
> --- a/include/media/hevc-ctrls.h
> +++ b/include/media/hevc-ctrls.h
> @@ -20,6 +20,7 @@
> #define V4L2_CID_STATELESS_HEVC_DECODE_PARAMS (V4L2_CID_CODEC_BASE + 1012)
> #define V4L2_CID_STATELESS_HEVC_DECODE_MODE (V4L2_CID_CODEC_BASE + 1015)
> #define V4L2_CID_STATELESS_HEVC_START_CODE (V4L2_CID_CODEC_BASE + 1016)
> +#define V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSETS (V4L2_CID_CODEC_BASE + 1017)
>
> /* enum v4l2_ctrl_type type values */
> #define V4L2_CTRL_TYPE_HEVC_SPS 0x0120
> @@ -316,6 +317,8 @@ struct v4l2_hevc_pred_weight_table {
> *
> * @bit_size: size (in bits) of the current slice data
> * @data_bit_offset: offset (in bits) to the video data in the current slice data
> + * @num_entry_point_offsets: specifies the number of entry point offset syntax
> + * elements in the slice header.
> * @nal_unit_type: specifies the coding type of the slice (B, P or I)
> * @nuh_temporal_id_plus1: minus 1 specifies a temporal identifier for the NAL unit
> * @slice_type: see V4L2_HEVC_SLICE_TYPE_{}
> @@ -358,7 +361,7 @@ struct v4l2_hevc_pred_weight_table {
> struct v4l2_ctrl_hevc_slice_params {
> __u32 bit_size;
> __u32 data_bit_offset;
> -
> + __u32 num_entry_point_offsets;
> /* ISO/IEC 23008-2, ITU-T Rec. H.265: NAL unit header */
> __u8 nal_unit_type;
> __u8 nuh_temporal_id_plus1;
> --
> 2.32.0
>