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

Jernej Škrabec
2022-05-30T21:24:46Z

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@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
> >>>
> >>>
> >>
> >>
> >
>
>