Re: [PATCH 06/10] media: uapi: h264: Cleanup DPB entry interface

[Jonas Karlman <jonas@kwiboo.se>]

Hi,

On 2020-07-24 21:08, Ezequiel Garcia wrote:
> Hello Jonas,
> 
> On Wed, 2020-07-22 at 21:52 +0000, Jonas Karlman wrote:
>> On 2020-07-15 22:22, Ezequiel Garcia wrote:
>>> As discussed recently, the current interface for the
>>> Decoded Picture Buffer is not enough to properly
>>> support field coding.
>>>
>>> This commit introduces enough semantics to support
>>> frame and field coding, and to signal how DPB entries
>>> are "used for reference".
>>>
>>> Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
>>> ---
>>>  .../media/v4l/ext-ctrls-codec.rst             | 46 ++++++++++++-------
>>>  drivers/media/v4l2-core/v4l2-h264.c           |  4 +-
>>>  drivers/staging/media/rkvdec/rkvdec-h264.c    |  8 ++--
>>>  include/media/h264-ctrls.h                    |  8 +++-
>>>  4 files changed, 42 insertions(+), 24 deletions(-)
>>>
>>> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>>> index dd8e5a2e8986..46d4c8c6ad47 100644
>>> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>>> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
>>> @@ -2058,10 +2058,35 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>>>      * - __s32
>>>        - ``bottom_field_order_cnt``
>>>        -
>>> +    * - enum :c:type:`v4l2_h264_dpb_reference`
>>> +      - ``reference``
>>> +      - Specifies how the DPB entry is referenced.
>>>      * - __u32
>>>        - ``flags``
>>>        - See :ref:`DPB Entry Flags <h264_dpb_flags>`
>>>  
>>> +.. c:type:: v4l2_h264_dpb_reference
>>> +
>>> +.. cssclass:: longtable
>>> +
>>> +.. flat-table::
>>> +    :header-rows:  0
>>> +    :stub-columns: 0
>>> +    :widths:       1 1 2
>>> +
>>> +    * - ``V4L2_H264_DPB_TOP_REF``
>>> +      - 0x1
>>> +      - The top field in field pair is used for
>>> +        short-term reference.
>>> +    * - ``V4L2_H264_DPB_BOTTOM_REF``
>>> +      - 0x2
>>> +      - The bottom field in field pair is used for
>>> +        short-term reference.
>>> +    * - ``V4L2_H264_DPB_FRAME_REF``
>>> +      - 0x3
>>> +      - The frame (or the top/bottom fields, if it's a field pair)
>>> +        is used for short-term reference.
>>> +
>>>  .. _h264_dpb_flags:
>>>  
>>>  ``DPB Entries Flags``
>>> @@ -2075,29 +2100,16 @@ enum v4l2_mpeg_video_h264_hierarchical_coding_type -
>>>  
>>>      * - ``V4L2_H264_DPB_ENTRY_FLAG_VALID``
>>>        - 0x00000001
>>> -      - The DPB entry is valid and should be considered
>>> +      - The DPB entry is valid (non-empty) and should be considered.
>>>      * - ``V4L2_H264_DPB_ENTRY_FLAG_ACTIVE``
>>>        - 0x00000002
>>> -      - The DPB entry is currently being used as a reference frame
>>> +      - The DPB entry is used for reference.
>>>      * - ``V4L2_H264_DPB_ENTRY_FLAG_LONG_TERM``
>>>        - 0x00000004
>>> -      - The DPB entry is a long term reference frame
>>> +      - The DPB entry is used for long-term reference.
>>>      * - ``V4L2_H264_DPB_ENTRY_FLAG_FIELD``
>>>        - 0x00000008
>>> -      - The DPB entry is a field reference, which means only one of the field
>>> -        will be used when decoding the new frame/field. When not set the DPB
>>> -        entry is a frame reference (both fields will be used). Note that this
>>> -        flag does not say anything about the number of fields contained in the
>>> -        reference frame, it just describes the one used to decode the new
>>> -        field/frame
>>> -    * - ``V4L2_H264_DPB_ENTRY_FLAG_BOTTOM_FIELD``
>>> -      - 0x00000010
>>> -      - The DPB entry is a bottom field reference (only the bottom field of the
>>> -        reference frame is needed to decode the new frame/field). Only valid if
>>> -        V4L2_H264_DPB_ENTRY_FLAG_FIELD is set. When
>>> -        V4L2_H264_DPB_ENTRY_FLAG_FIELD is set but
>>> -        V4L2_H264_DPB_ENTRY_FLAG_BOTTOM_FIELD is not, that means the
>>> -        DPB entry is a top field reference
>>> +      - The DPB entry is a single field or a complementary field pair.
>>>  
>>>  ``V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE (enum)``
>>>      Specifies the decoding mode to use. Currently exposes slice-based and
>>> diff --git a/drivers/media/v4l2-core/v4l2-h264.c b/drivers/media/v4l2-core/v4l2-h264.c
>>> index edf6225f0522..306a51683606 100644
>>> --- a/drivers/media/v4l2-core/v4l2-h264.c
>>> +++ b/drivers/media/v4l2-core/v4l2-h264.c
>>> @@ -66,10 +66,10 @@ v4l2_h264_init_reflist_builder(struct v4l2_h264_reflist_builder *b,
>>>  		else
>>>  			b->refs[i].frame_num = dpb[i].frame_num;
>>>  
>>> -		if (!(dpb[i].flags & V4L2_H264_DPB_ENTRY_FLAG_FIELD))
>>> +		if (dpb[i].reference & V4L2_H264_DPB_FRAME_REF)
>>
>> This looks wrong, should probably use ==,
>>
>> dpb[i].reference == V4L2_H264_DPB_FRAME_REF
>>
>> else this would match any reference value.
>>
>>>  			pic_order_count = min(dpb[i].top_field_order_cnt,
>>>  					      dpb[i].bottom_field_order_cnt);
>>> -		else if (dpb[i].flags & V4L2_H264_DPB_ENTRY_FLAG_BOTTOM_FIELD)
>>> +		else if (dpb[i].reference & V4L2_H264_DPB_BOTTOM_REF)
>>>  			pic_order_count = dpb[i].bottom_field_order_cnt;
>>>  		else
>>>  			pic_order_count = dpb[i].top_field_order_cnt;
>>> diff --git a/drivers/staging/media/rkvdec/rkvdec-h264.c b/drivers/staging/media/rkvdec/rkvdec-h264.c
>>> index 7b66e2743a4f..57539c630422 100644
>>> --- a/drivers/staging/media/rkvdec/rkvdec-h264.c
>>> +++ b/drivers/staging/media/rkvdec/rkvdec-h264.c
>>> @@ -953,11 +953,11 @@ static void config_registers(struct rkvdec_ctx *ctx,
>>>  			     RKVDEC_COLMV_USED_FLAG_REF;
>>>  
>>>  		if (!(dpb[i].flags & V4L2_H264_DPB_ENTRY_FLAG_FIELD))
>>> -			refer_addr |= RKVDEC_TOPFIELD_USED_REF |
>>> -				      RKVDEC_BOTFIELD_USED_REF;
>>> -		else if (dpb[i].flags & V4L2_H264_DPB_ENTRY_FLAG_BOTTOM_FIELD)
>>> +			refer_addr |= RKVDEC_FIELD_REF;
>>> +
>>> +		if (dpb[i].reference & V4L2_H264_DPB_TOP_REF)
>>>  			refer_addr |= RKVDEC_BOTFIELD_USED_REF;
>>> -		else
>>> +		else if (dpb[i].reference & V4L2_H264_DPB_BOTTOM_REF)
>>
>> This should probably be if and not else if, and BOTFIELD/TOPFIELD_USED_REF
>> seems to be mixed up.
>>
>> I have only taken a quick look so far, I will update ffmpeg and runtime test
>> later this weekend, will get back with result and full review on Sunday evening.
>>
> 
> Thanks that would be useful.
> 
> However, keep in mind this series is specifically concerned
> with the uAPI review.
> 
> This is not supposed to fix the field coded support, or anything
> else in any driver.
> 
> IMO, at this stage, fixing drivers is somewhat lower priority
> than discussing and stabilizing the uAPI.

I have now tested rkvdec on a RK3328 device and needed to do 3 fixups, see [1].
Initial ffmpeg update using update h264 uapi is located at [2], the ffmpeg
update still needs to be tested with cedrus and hantro.

So far I have not seen any issue with the uapi changes.

Q: ffmpeg will not try to set SLICE_PARAMS or PRED_WEIGHT ctrls for
DECODE_MODE_SLICE_BASED, should userspace check if ctrl exists or is using
DECODE_MODE value okay?

I have also pushed an updated WIP branch at [3] containing high 10,
field encoded and hevc work.

[1] https://github.com/Kwiboo/linux-rockchip/compare/b6b91f27c0cb33520e954e7bb2550e0e07ed4d85...b82b6e93feb9ca44d2c677f25416cf6345f0114d
[2] https://github.com/Kwiboo/FFmpeg/commits/v4l2-request-hwaccel-4.3.1
[3] https://github.com/Kwiboo/linux-rockchip/commits/linuxtv-rkvdec-work-in-progress

Best regards,
Jonas

> 
> Thanks,
> Ezequiel
> 
>