Re: [RFC] METADATA design using V4l2 Request API

[dikshita@codeaurora.org]

Hi Hans,

Thanks for the review.

On 2020-05-26 16:27, Hans Verkuil wrote:
> Hi Dikshita,
> 
> My apologies for the delay, this was (mostly) due to various vacation 
> days.
> 
> On 08/05/2020 08:21, Dikshita Agarwal wrote:
>> There are many commercialized video use cases which needs metadata 
>> info
>> to be circulated between v4l2 client and v4l2 driver.
>> 
>> METADATA has following requirements associated:
>> •Metadata is an optional info available for a buffer. It is not 
>> mandatorily for every buffer.
>>  For ex. consider metadata ROI (Region Of Interest). ROI is specified 
>> by clients to indicate
>>  the region where enhanced quality is desired. This metadata is given 
>> as an input information
>>  to encoder output plane. Client may or may not specify the ROI for a 
>> frame during encode as
>>  an input metadata. Also if the client has not provided ROI metadata 
>> for a given frame,
>>  it would be incorrect to take the metadata from previous frame. If 
>> the data and
>>  metadata is asynchronous, it would be difficult for hardware to 
>> decide if it
>>  needs to wait for metadata buffer or not before processing the input 
>> frame for encoding.
>> •Synchronize the buffer requirement across both the video node/session
>>  (incase metadata is being processed as a separate v4l2 video 
>> node/session).
>>  This is to avoid buffer starvation.
>> •Associate the metadata buffer with the data buffer without adding any 
>> pipeline delay
>>  in waiting for each other. This is applicable both at the hardware 
>> side (the processing end)
>>  and client side (the receiving end).
>> •Low latency usecases like WFD/split rendering/game streaming/IMS have 
>> sub-50ms e2e latency
>>  requirements, and it is not practical to stall the pipeline due to 
>> inherent framework latencies.
>>  High performance usecase like high-frame rate playback/record can 
>> lead to frame loss during any pipeline latency.
>> 
>> To address all above requirements, we used v4l2 Request API as 
>> interlace.
>> 
>> As an experiment, We have introduced new control 
>> V4L2_CID_MPEG_VIDEO_VENUS_METADATA
>> to contain the METADATA info. Exact controls can be finalized once the 
>> interface is discussed.
>> 
>> For setting metadata from userspace to kernel, let say on encode 
>> output plane,
>> following code sequence was followed
>> 1. Video driver is registering for media device and creating a media 
>> node in /dev
>> 2. Request fd is allocated by calling MEDIA_IOC_REQUEST_ALLOC IOCTL on 
>> media fd.
>> 3. METADATA configuration is being applied on request fd using 
>> VIDIOC_S_EXT_CTRLS IOCTL
>>    and the same request fd is added to buf structure structure before 
>> calling VIDIOC_QBUF on video fd.
>> 4. The same request is queued through MEDIA_REQUEST_IOC_QUEUE IOCTL to 
>> driver then, as a result
>>    to which METADATA control will be applied to buffer through S_CTRL.
>> 5. Once control is applied and request is completed, 
>> MEDIA_REQUEST_IOC_REINIT IOCTL is called
>>    to re-initialize the request.
> 
> This is fine and should work well. It's what the Request API is for,
> so no problems here.
> 
>> 
>> We could achieve the same on capture plane as well by removing few 
>> checks present currently
>> in v4l2 core which restrict the implementation to only output plane.
> 
> Why do you need the Request API for the capture side in a
> memory-to-memory driver? It is not
> clear from this patch series what the use-case is. There are reasons
> why this is currently
> not allowed. So I need to know more about this.
> 
> Regards,
> 
> 	Hans
> 
we need this for use cases like HDR10+ where metadata info is part of 
the bitstream.
To handle such frame specific data, support for request api on capture 
plane would be needed.

Thanks,
Dikshita
>> 
>> We profiled below data with this implementation :
>> 1. Total time taken ( round trip ) for setting up control data on 
>> video driver
>>    with VIDIOC_S_EXT_CTRLS, QBUF and Queue Request: 737us
>> 2. Time taken for first QBUF on Output plane to reach driver with 
>> REQUEST API enabled (One way): 723us
>> 3. Time taken for first QBUF on Output plane to reach driver without 
>> REQUEST API (One way) : 250us
>> 4. Time taken by each IOCTL to complete ( round trip ) with REQUEST 
>> API enabled :
>>     a. VIDIOC_S_EXT_CTRLS : 201us
>>     b. VIDIOC_QBUF : 92us
>>     c. MEDIA_REQUEST_IOC_QUEUE: 386us
>> 
>> Kindly share your feedback/comments on the design/call sequence.
>> Also as we experimented and enabled the metadata on capture plane as 
>> well, please comment if any issue in
>> allowing the metadata exchange on capture plane as well.
>> 
>> Reference for client side implementation can be found at [1].
>> 
>> Thanks,
>> Dikshita
>> 
>> [1] 
>> https://git.linaro.org/people/stanimir.varbanov/v4l2-encode.git/log/?h=dikshita/request-api
>> 
>> Dikshita Agarwal (3):
>>   Register for media device
>>     - Initialize and register for media device
>>     - define venus_m2m_media_ops
>>     - Implement APIs to register/unregister media controller.
>>   Enable Request API for output buffers
>>     - Add dependency on MEDIA_CONTROLLER_REQUEST_API in Kconfig.
>>     - Initialize vb2 ops buf_out_validate and buf_request_complete.
>>     - Add support for custom Metadata control 
>> V4L2_CID_MPEG_VIDEO_VENUS_METADATA
>>     - Implemeted/Integrated APIs for Request setup/complete.
>>   Enable Request API for Capture Buffers
>> 
>>  drivers/media/common/videobuf2/videobuf2-v4l2.c |   4 +-
>>  drivers/media/platform/Kconfig                  |   2 +-
>>  drivers/media/platform/qcom/venus/core.h        |  36 ++++
>>  drivers/media/platform/qcom/venus/helpers.c     | 247 
>> +++++++++++++++++++++++-
>>  drivers/media/platform/qcom/venus/helpers.h     |  15 ++
>>  drivers/media/platform/qcom/venus/venc.c        |  63 +++++-
>>  drivers/media/platform/qcom/venus/venc_ctrls.c  |  61 +++++-
>>  drivers/media/v4l2-core/v4l2-ctrls.c            |  10 +
>>  drivers/media/v4l2-core/v4l2-mem2mem.c          |  17 +-
>>  include/media/v4l2-ctrls.h                      |   1 +
>>  include/media/venus-ctrls.h                     |  22 +++
>>  11 files changed, 465 insertions(+), 13 deletions(-)
>>  create mode 100644 include/media/venus-ctrls.h
>>