Video RTIO demo

[josuah]

In some area, RTIO is used to increase performance at a slight extra cost in code size.

For video, it seems like a partial RTIO-like flow was already adopted by @loicpoulain in video APIs out of kernel primitives (the same week RTIO was introduced), so switching to RTIO actually reduces the amount of code in drivers and simplify the video APIs.

 drivers/video/Kconfig                    |   1 +
 drivers/video/video_common.c             |  25 +++++-
 drivers/video/video_sw_generator.c       |  99 ++++++-----------------
 include/zephyr/drivers/video.h           | 192 +++++++++-----------------------------------
 samples/drivers/video/capture/src/main.c |  48 +++++++----
 5 files changed, 119 insertions(+), 246 deletions(-)

API functions removed as now available through RTIO APIs:

• .enqueue
• .dequeue
• .flush
• .set_signal (the polling API)

API function added:

• .iodev_submit

The sample main.c did not go down in size. This initial PR adds a naive implementation that exposes all the RTIO internals directly, allowing discussion with the RTIO developers and Video developers and users about what wrappers to implement.

Keeping the low-level exposed is also a good opportunity to allow application libraries to wrap video APIs in higher-level and efficient userspace APIs.

[josuah]

Current status:

• native_sim/native/64 works.
• CI does not work as zephyr,video-emul-rx is not converted yet.

[josuah]

For anyone investigating RTIO, the implementation of the engine is actually nimble!

• https://github.com/zephyrproject-rtos/zephyr/tree/main/subsys/rtio

Other useful resources:

• Talk from a few days ago: Real-Time I/O (RTIO) for Developing Real-Time Zephyr Applications - Luis Ubieda, Croxel
• Slides of the talk: [pdf]
• Discord discussion: https://discord.com/channels/720317445772017664/1389889080908582973
• The sensors simple rtio_iodev_api definition.
• The i2c/rtio_loopback, rtio/batch_sensor_processing samples
• The ongoing ADC RTIO pull request adopting sensor-like RTIO API wrappers: ADC stream API #90285

And the ongoing discussionso with RTIO developers (for grasping the RTIO model), and Zephyr/Linux develoeprs (for grasping the V4L2 model) through this year!

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[ngphibang]

Thank you for the this implementation. I tried to quickly implement the necessary stuffs to generalize this into the framework in #92370. It is faster to illustrate the idea, hope you don't mind.

[josuah]

I tried to quickly implement the necessary stuffs to generalize this into the framework in #92370. It is faster to illustrate the idea, hope you don't mind.

I left the user-side APIs very crude on purpose to make it easier to design an API on #92370

[github-actions]

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[josuah]

This is superseded by #92370 so can be closed.