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

[Jernej Škrabec]

Dne ponedeljek, 30. maj 2022 ob 15:49:57 CEST je Hans Verkuil napisal(a):
> On 30/05/2022 11:18, Hans Verkuil wrote:
> > 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.
> 
> Digging more into this made me realize that this doesn't actually help for 
this
> particular case.
> 
> I would lean towards your second suggestion of adding up all 
num_entry_point_offsets
> of previous slices.

Just one question/clarification about dynamic arrays - does driver need to 
reserve maximum amount of memory for dynamic array control at initialization 
time? If so, this would still be problematic, since there cound be a huge 
amount of entry points in theory.

Best regards,
Jernej

> 
> Regards,
> 
> 	Hans
> 
> > 
> > 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@xxxxxxxxxxxxx>
> >>> ---
> >>>  .../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
> >>>
> >>>
> >>
> >>
> > 
> 
>