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

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Date:   Tue, 9 Jul 2019 19:19:36 -0300
From:   Helen Koike <helen.koike@...labora.com>
To:     André Almeida <andrealmeid@...labora.com>,
        linux-media@...r.kernel.org
Cc:     mchehab@...nel.org, hverkuil@...all.nl, kernel@...labora.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/7] media: vimc: Add a V4L2 output device

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?

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
>