linux-kernel - Re: [PATCH v2 0/6] media: cedrus: h264: Support multi-slice frames

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Date:   Tue, 1 Oct 2019 00:43:34 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Jernej Škrabec <jernej.skrabec@...l.net>
Cc:     mchehab@...nel.org, paul.kocialkowski@...tlin.com,
        mripard@...nel.org, pawel@...iak.com, m.szyprowski@...sung.com,
        kyungmin.park@...sung.com, tfiga@...omium.org, wens@...e.org,
        gregkh@...uxfoundation.org, boris.brezillon@...labora.com,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-arm-kernel@...ts.infradead.org,
        ezequiel@...labora.com, jonas@...boo.se
Subject: Re: [PATCH v2 0/6] media: cedrus: h264: Support multi-slice frames

On 10/1/19 12:27 AM, Jernej Škrabec wrote:
> Dne ponedeljek, 30. september 2019 ob 10:10:48 CEST je Hans Verkuil 
> napisal(a):
>> On 9/29/19 10:00 PM, Jernej Skrabec wrote:
>>> This series adds support for decoding multi-slice H264 frames along with
>>> support for V4L2_DEC_CMD_FLUSH and V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF.
>>>
>>> Code was tested by modified ffmpeg, which can be found here:
>>> https://github.com/jernejsk/FFmpeg, branch mainline-test
>>> It has to be configured with at least following options:
>>> --enable-v4l2-request --enable-libudev --enable-libdrm
>>>
>>> Samples used for testing:
>>> http://jernej.libreelec.tv/videos/h264/BA1_FT_C.mp4
>>> http://jernej.libreelec.tv/videos/h264/h264.mp4
>>>
>>> Command line used for testing:
>>> ffmpeg -hwaccel drm -hwaccel_device /dev/dri/card0 -i h264.mp4 -pix_fmt
>>> bgra -f fbdev /dev/fb0
>>>
>>> Please note that V4L2_DEC_CMD_FLUSH was not tested because I'm
>>> not sure how. ffmpeg follows exactly which slice is last in frame
>>> and sets hold flag accordingly. Improper usage of hold flag would
>>> corrupt ffmpeg assumptions and it would probably crash. Any ideas
>>> how to test this are welcome!
>>
>> It can be tested partially at least: if ffmpeg tells you it is the last
>> slice, then queue the slice with the HOLD flag set, then call FLUSH
>> afterwards. This should clear the HOLD flag again. In this case the queued
>> buffer is probably not yet processed, so the flag is cleared before the
>> decode job starts.
>>
>> You can also try to add a sleep before calling FLUSH to see what happens
>> if the last queued buffer is already decoded.
> 
> Ok, I tried following code:
> https://github.com/jernejsk/FFmpeg/blob/flush_test/libavcodec/
> v4l2_request.c#L220-L233
> 
> But results are not good. It seems that out_vb in flush command is always NULL 
> and so it always marks capture buffer as done, which leads to kernel warnings.
> 
> dmesg output with debugging messages is here: http://ix.io/1Ks8
> 
> Currently I'm not sure what is going on. Shouldn't be output buffer queued and 
> waiting to MEDIA_REQUEST_IOC_QUEUE which is executed after flush command as it 
> can be seen from ffmpeg code linked above?

Argh, I forgot about the fact that this uses requests.

The FLUSH should happen *after* the MEDIA_REQUEST_IOC_QUEUE ioctl. Otherwise
it has no effect. As long as the request hasn't been queued, the buffer is also
not queued to the driver, so out_vb will indeed be NULL.

Sorry for the confusion.

Regards,

	Hans

> 
> Best regards,
> Jernej
> 
>>
>> Regards,
>>
>> 	Hans
>>
>>> Thanks to Jonas for adjusting ffmpeg.
>>>
>>> Please let me know what you think.
>>>
>>> Best regards,
>>> Jernej
>>>
>>> Changes from v1:
>>> - added Rb tags
>>> - updated V4L2_DEC_CMD_FLUSH documentation
>>> - updated first slice detection in Cedrus
>>> - hold capture buffer flag is set according to source format
>>> - added v4l m2m stateless_(try_)decoder_cmd ioctl helpers
>>>
>>> Hans Verkuil (2):
>>>   vb2: add V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF
>>>   videodev2.h: add V4L2_DEC_CMD_FLUSH
>>>
>>> Jernej Skrabec (4):
>>>   media: v4l2-mem2mem: add stateless_(try_)decoder_cmd ioctl helpers
>>>   media: cedrus: Detect first slice of a frame
>>>   media: cedrus: h264: Support multiple slices per frame
>>>   media: cedrus: Add support for holding capture buffer
>>>  
>>>  Documentation/media/uapi/v4l/buffer.rst       | 13 ++++++
>>>  .../media/uapi/v4l/vidioc-decoder-cmd.rst     | 10 +++-
>>>  .../media/uapi/v4l/vidioc-reqbufs.rst         |  6 +++
>>>  .../media/videodev2.h.rst.exceptions          |  1 +
>>>  .../media/common/videobuf2/videobuf2-v4l2.c   |  8 +++-
>>>  drivers/media/v4l2-core/v4l2-mem2mem.c        | 35 ++++++++++++++
>>>  drivers/staging/media/sunxi/cedrus/cedrus.h   |  1 +
>>>  .../staging/media/sunxi/cedrus/cedrus_dec.c   | 11 +++++
>>>  .../staging/media/sunxi/cedrus/cedrus_h264.c  | 11 ++++-
>>>  .../staging/media/sunxi/cedrus/cedrus_hw.c    |  8 ++--
>>>  .../staging/media/sunxi/cedrus/cedrus_video.c | 14 ++++++
>>>  include/media/v4l2-mem2mem.h                  | 46 +++++++++++++++++++
>>>  include/media/videobuf2-core.h                |  3 ++
>>>  include/media/videobuf2-v4l2.h                |  5 ++
>>>  include/uapi/linux/videodev2.h                | 14 ++++--
>>>  15 files changed, 175 insertions(+), 11 deletions(-)
> 
> 
> 
>