Re: [PATCH v6 11/17] media: uapi: Add V4L2_CID_STATELESS_HEVC_ENTRY_POINT_OFFSETS control

Hans Verkuil
2022-05-30T09:18:41Z

On 29/05/2022 08:40, Jernej Škrabec wrote:
> Hi!
>
> This series looks very good and I plan to test it shortly on Cedrus, but I
> have one major concern below.
>
> Dne petek, 27. maj 2022 ob 16:31:28 CEST je Benjamin Gaignard napisal(a):
>> 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.
>
> Slice control by itself is variable length array, so you would actually need
> 2D variable array for entry points which is not supported. However, easy
> workaround for that is to flatten 2D array to 1D and either have another slice
> control field which would tell first entry point index for convenience or let
> driver calculate it by adding up all num_entry_point_offsets of previous
> slices.
>
> Hans, what do you think?

If I would support 2D variable array sizes, wouldn't that be more elegant?

The current implementation doesn't support that, but as the commit log for
patch 1/17 says:

"Currently dynamically sized arrays are limited to one dimensional arrays,
but that might change in the future if there is a need for it."

Let me know if you agree, and I'll try to implement this. It's been a while
since I last looked at this, so I'm not sure how much work it is, but it is
probably worth a shot.

Regards,

Hans

>
> Note, it seems that H265 decoding on Cedrus still works without entry points,
> so this problem can be solved later. I'm not sure what we lose with that but
> it was suggested that this could influence speed or error resilience or both.
> However, I think we're close to solve it, so I'd like to do that now.
>
> Best regards,
> Jernej
>
>>
>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
>> ---
>> .../userspace-api/media/v4l/ext-ctrls-codec.rst | 11 +++++++++++
>> drivers/media/v4l2-core/v4l2-ctrls-defs.c | 5 +++++
>> include/media/hevc-ctrls.h | 5 ++++-
>> 3 files changed, 20 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 0796b1563daa..05228e280f66 100644
>> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>> @@ -3010,6 +3010,9 @@ 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.
>> * - __u8
>> - ``nal_unit_type``
>> - Specifies the coding type of the slice (B, P or I).
>> @@ -3150,6 +3153,14 @@ 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.
>> +
>> ``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 a3c829ef531a..1319cb99ae3f 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
>> @@ -318,6 +319,8 @@ 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_{}
>> @@ -360,7 +363,7 @@ 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
>>
>>
>
>