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

Nicolas Dufresne
2022-06-01T16:21:07Z

Le mardi 31 mai 2022 à 20:20 +0200, Jernej Škrabec a écrit :
> Dne torek, 31. maj 2022 ob 08:58:46 CEST je Benjamin Gaignard napisal(a):
> >
> > Le 30/05/2022 à 23:24, Jernej Škrabec a écrit :
> > > 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.
> >
> > When adding the control the driver could set .dims field to specify
> > the max number of accepted slices.
> > I have added '#define V4L2_HEVC_SLICE_MAX_COUNT 600' that you could use
> > for this field. It is the value we have found when using slices with RKVDEC
> > driver.
>
> Is this maximum value applicable only to RKVDEC or is universal? Anyway, this
> means maximum offset points control for Cedrus would be 600 * 1024 (max. offset
> points supported per slice) * 4 ~= 2.4 MB, which is a lot for one control, but
> I can live with that...

I believe its defined following "Table A.8 – General tier and level limits".
With the assumption there will never be a level 7 (which I think is fair). If
anyone saw other reasons for this limit, let me know.

This is a worse case scenario, this is quite unlikely in practice, so while
performance might be a disaster if your craft a stream for that case, I don't
think it will ever happen in real life.

>
> Best regards,
> Jernej
>
> >
> > Regards,
> > Benjamin
> >
> > >
> > > 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
> > > > > > >
> > > > > > >
> > > > > >
> > > >
> > >
> >
>
>