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

John Cox
2022-06-10T14:09:00Z

On Mon, 30 May 2022 15:49:57 +0200, you wrote:

>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.

Whilst I don't personally need this array I also think that a 1-D array
is the correct answer here. Any implementation that does need this info
is going to have to be going through the slice array and this array
together so adding the num_entry_point_offsets together is trivial.

Regards

John Cox

>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
>>>>
>>>>
>>>
>>>
>>