The video4linux subsystem of the kernel is a very large API with many ioctls, settings, options and capabilities. This poses a problem both for the kernel developer and for the application developer. Since early this year major improvements have been made to both the v4l2-compliance utility for verifying drivers, and to the virtual video driver that applications can use as a reference input. This presentation will explain and demonstrate this utility and driver and show how to use them to ensure your driver or application works correctly. Hans Verkuil, Cisco Systems Norway

1. Testing Video4Linux
Applications and Drivers
Hans Verkuil
Cisco Systems Norway
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2. Utilities
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3. Utilities
● v4l2-compliance: V4L2 compliance driver testing.
● v4l2-ctl: command line Swiss army knife for v4l2.
● qv4l2: Qt test application.
● v4l2-dbg: allows access to DBG_G_CHIP_INFO,
DBG_G/S_REGISTER.
● Core debugging: 'echo 1 >/sys/class/video4linux/video0/debug'.
● 1: show ioctl name
● 2: show arguments as well
● V4L2 support was added to valgrind 3.10.
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4. Utilities: v4l2-compliance
● Started 6 years ago.
● In February tests for streaming were added.
● New drivers must pass the compliance tests.
● Close to 900 tests are performed.
● Covers all 82 V4L2 ioctls except 9 ioctls: the cropping and selection
ioctls, the overlay ioctls and the new VIDIOC_QUERY_EXT_CTRL ioctl.
● It is more strict than the V4L2 specification: it assumes drivers use the
correct core frameworks which means that there is no excuse to e.g.
support VIDIOC_S_CTRL but not VIDIOC_S_EXT_CTRLS.
● Always compile from the v4l-utils git repository to get the latest tests.
● Demo!
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5. Utilities: v4l2-ctl and qv4l2
● 'Golden Reference' utilities: v4l2-ctl can control V4L2 devices from the
command line, qv4l2 is the Qt4 GUI equivalent.
● Kept in sync with the kernel and support for new V4L2 kernel APIs is
always added to these utilities.
● v4l2-ctl is ideal for embedded systems.
● qv4l2 is ideal for interactive testing.
● Demo!
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6. Test Drivers
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7. Test Drivers
● vivi: simple but non-standard video capture. Available for kernels < 3.18.
● mem2mem_testdev: memory-to-memory test driver
● vivid: video capture & output, vbi capture & output, radio receiver &
transmitter, software defined radio capture. Closely emulates what 'real'
hardware will do. Replaces vivi in kernel 3.18.
● Most V4L2 devices only support a (very) limited subset of the V4L2 API.
Without test drivers (or a huge collection of hardware) it is impossible to
test your application, but with the vivid driver you can.
● Demo!
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8. Cropping, Scaling and Composing
HDMI Cable HDMI Receiver Hardware
HDMI
1280x720
Scaled
1280x720
Cropped
1024x576
Composed
1280x720
DMA Engine
Memory
openGL
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9. Resources
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10. Resources
● Linux Media Infrastructure API: http://linuxtv.org/downloads/v4l-dvb-apis.
Latest version: http://hverkuil.home.xs4all.nl/spec/media.html
● Documentation/video4linux/v4l2-framework.txt and v4l2-controls.txt
● include/media/videobuf2-core.h
● Upstream media git repository containing vivid driver:
http://git.linuxtv.org/media_tree.git
● Skeleton driver: Documentation/video4linux/v4l2-pci-skeleton.c
● v4l-utils git repository: http://git.linuxtv.org/v4l-utils.git
● linux-media mailinglist & irc channel: http://linuxtv.org/lists.php
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11. Questions?
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