To test CEC on an RPi3:
1) Google for "HDMI Specification 1.4 pdf": the first hit is the pdf which contains the 1.4 CEC specification.
2) See the "Making a CEC debugger"  section here: https://hverkuil.home.xs4all.nl/cec-status.txt
Luckily you don't need all that for testing CEC.
This patch should be enough: https://git.linuxtv.org/hverkuil/media_tree.git/commit/?h=cec-gpio&id=8180675e60be7079f3e27a8e91fe5092a8950483
(leave out the hpd-gpio entries, you don't need those)
make sure the media/platform/cec-gpio driver is enabled.
Use a jumper cable to connect the CE0 and CE1 gpio pins together. The CE0 and CE1 pins each form a CEC adapter, so they can talk to one another.
BTW, some of the contents of my cec-status.txt file will eventually end up in the kernel documentation.
Once 4.14 has been merged then there is also a native CEC adapter for the HDMI output of the RPi3.
For testing this it not really needed.
hverkuil: thanks!
mchehab2: The changes are already addressed by my current patch series.
The reason why it's in v4l2-fwnode.c comes from v4l2-of.c directly. So the reason for the current state is historical.
sailus, thanks! I'll then just skip this file
I'm in the process of ensuring that the kAPI is in sync with the implementation
hopefully, it will be on 4.15 :-)
mchehab2: Yes, I'm targetting that. :-)