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

Benjamin Gaignard
2022-05-31T06:58:51Z

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.

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