linux-kernel - Re: [PATCH 0/7] media: vimc: Add a V4L2 output device

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Date:   Sat, 13 Jul 2019 12:03:05 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     André Almeida <andrealmeid@...labora.com>,
        Helen Koike <helen.koike@...labora.com>,
        linux-media@...r.kernel.org
Cc:     mchehab@...nel.org, kernel@...labora.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/7] media: vimc: Add a V4L2 output device

On 7/12/19 5:38 PM, André Almeida wrote:
> Hello,
> 
> On 7/10/19 4:33 AM, Hans Verkuil wrote:
>> On 7/10/19 12:19 AM, Helen Koike wrote:
>>> Hi André,
>>>
>>> Thanks for the patches.
>>>
>>> On 7/2/19 12:47 PM, André Almeida wrote:
>>>> Hello,
>>>>
>>>> This patch adds a V4L2 output device on vimc, that comply with V4L2 API
>>>> for video output. If there is an output device and a capture device at the
>>>> same pipeline, one can get a video loopback pipeline feeding frames at
>>>> the output and then seeing them at the capture. It's possible to insert
>>>> vimc submodules at the pipeline to modify the image (e.g. a scaler).
>>>>
>>>> If one starts a streaming at the capture, with the output off, the
>>>> capture will display a noisy frame. If one starts a streaming at the
>>>> output with the capture off, the output will just consume the buffers,
>>>> without sending them to the pipeline. If both output and capture are
>>>> streaming, the loopback will happen.
>>> I understand why it is done like this in vivid, but I was wondering, if we
>>> have a pipeline like:
>>> output -> capture
>>> Shouldn't streaming from the capture just stalls if there is no frame
>>> available in the output (i.e. streaming in the output is off) ? But then I'm
>>> not sure what the framerate in the capture would mean.
>>>
>>> Hans, what do you think?
>> If you set up the pipeline like this:
>>
>> Video Output -> Scaler -> Video Capture
> 
> If the capture will stall if there's no frame from the video output, how
> can I add support for this kind of pipeline at test-media? It would be
> required to send frames to the output device while running
> `v4l2-compliance` at the capture device to make testing possible.

The compliance test doesn't support such devices at the moment.

I think a new option (or options) are needed to tell the compliance test
that the capture and output video devices together constitute an m2m device.

Regards,

	Hans

> 
> Thanks,
>     André
> 
>> Then this is a mem2mem device (except with two separate video devices) and
>> framerate doesn't apply anymore. And video capture will just stall if there
>> is no video output frame provided.
>>
>> It's how e.g. omap3isp works.
>>
>> Regards,
>>
>> 	Hans
>>
>>> Thanks,
>>> Helen
>>>
>>>> The patches 1 and 2 provide some ground to create the output
>>>> device. The patch 3 creates the device and modify how the vimc-streamer
>>>> was dealing with the s_stream callback on other vimc modules, to make
>>>> simpler implementing this callback at vimc-output. Patch 4 change the
>>>> behavior of the pipeline in order to be closer to a real life hardware.
>>>> Patches 5-7 updates the default pipeline and the documentation to
>>>> include the new output device.
>>>>
>>>> This is the result of v4l2-compliance after this patch series:
>>>> $ v4l2-compliance -m0 -s50
>>>> Grand Total for vimc device /dev/media0: 476, Succeeded: 476, Failed: 0,
>>>> Warnings: 0
>>>>
>>>> A git tree up to date with media-master and with this changes can be found
>>>> at: https://gitlab.collabora.com/tonyk/linux/tree/vimc/output
>>>>
>>>> In order to test it, one can follow these instructions:
>>>>
>>>> 1 - Configure the pipeline (requires v4l-utils):
>>>>
>>>> $ media-ctl -d platform:vimc -V '"Sensor A":0[fmt:SBGGR8_1X8/640x480]'
>>>> $ media-ctl -d platform:vimc -V '"Debayer A":0[fmt:SBGGR8_1X8/640x480]'
>>>> $ media-ctl -d platform:vimc -V '"Sensor B":0[fmt:SBGGR8_1X8/640x480]'
>>>> $ media-ctl -d platform:vimc -V '"Debayer B":0[fmt:SBGGR8_1X8/640x480]'
>>>> $ v4l2-ctl -z platform:vimc -d "RGB/YUV Capture" -v width=1920,height=1440
>>>> $ v4l2-ctl -z platform:vimc -d "Raw Capture 0" -v pixelformat=BA81
>>>> $ v4l2-ctl -z platform:vimc -d "Raw Capture 1" -v pixelformat=BA81
>>>> $ v4l2-ctl -z platform:vimc -e "RGB/YUV Input" -v width=640,height=480
>>>>
>>>> 2 - Use a userspace application:
>>>> 2.a gst-launch (requires gstreamer and gst-plugins-good):
>>>>
>>>> Feed frames into the output and grab from the capture (rescaled for
>>>> convenience):
>>>>
>>>> $ gst-launch-1.0 videotestsrc pattern=ball ! \
>>>> 	video/x-raw,width=640,height=480,format=RGB \
>>>> 	! v4l2sink device=/dev/video2 v4l2src device=/dev/video3 ! \
>>>> 	video/x-raw,width=1920,height=1440,format=RGB ! videoscale ! \
>>>> 	video/x-raw,width=640,height=480 ! videoconvert ! ximagesink
>>>>
>>>> 2.b qv4l2 (requires v4l-utils):
>>>>
>>>> Open the output device:
>>>>
>>>> $ qv4l2 -d2
>>>>
>>>> Open the capture device:
>>>>
>>>> $ qv4l2 -d3
>>>>
>>>> Start the streaming at both, at any order. You can change the frame
>>>> content at "Test Pattern Generator" -> "Test Pattern" on the output.
>>>>
>>>> Thanks,
>>>> 	André
>>>>
>>>> André Almeida (7):
>>>>   media: vimc: Create video module
>>>>   media: vimc: video: Add write file operation
>>>>   media: vimc: Create a V4L2 output device
>>>>   media: vimc: Send null buffer through the pipeline
>>>>   media: vimc: core: Add output device on the pipeline
>>>>   media: vimc.dot: Update default topology diagram
>>>>   media: vimc.rst: Add output device
>>>>
>>>>  Documentation/media/v4l-drivers/vimc.dot    |   4 +-
>>>>  Documentation/media/v4l-drivers/vimc.rst    |  12 +-
>>>>  drivers/media/platform/vimc/Makefile        |   4 +-
>>>>  drivers/media/platform/vimc/vimc-capture.c  | 356 +++----------------
>>>>  drivers/media/platform/vimc/vimc-common.h   |   5 +-
>>>>  drivers/media/platform/vimc/vimc-core.c     |   7 +-
>>>>  drivers/media/platform/vimc/vimc-debayer.c  |  14 +-
>>>>  drivers/media/platform/vimc/vimc-output.c   | 362 ++++++++++++++++++++
>>>>  drivers/media/platform/vimc/vimc-scaler.c   |  13 +-
>>>>  drivers/media/platform/vimc/vimc-sensor.c   |  10 +-
>>>>  drivers/media/platform/vimc/vimc-streamer.c |  24 +-
>>>>  drivers/media/platform/vimc/vimc-video.c    | 273 +++++++++++++++
>>>>  drivers/media/platform/vimc/vimc-video.h    | 130 +++++++
>>>>  13 files changed, 849 insertions(+), 365 deletions(-)
>>>>  create mode 100644 drivers/media/platform/vimc/vimc-output.c
>>>>  create mode 100644 drivers/media/platform/vimc/vimc-video.c
>>>>  create mode 100644 drivers/media/platform/vimc/vimc-video.h
>>>>