scheduler: add HDMI switching

[escoand]

Add ability to switch HDMI connected displays with the scheduler as well.
Maybe we should rename the variables from BACKLIGHT to DISPLAY.

My RPi display is not usable currently. Is somebody willing to test it with this change?

[escoand]

I've to realize that's not gonna work as the cec-client on alpine has no RPi support compiled.

[escoand]

Tested Debian as well. cec-client and tvservice are hanging on my RPi2.

[escoand]

finally got a working solution, we have to build libcec by hand to get RPi support

[escoand]

@dansku @chrisys @shaunmulligan are u interested in upstreaming this?

[escoand]

Just for reference the alpine bug for this https://gitlab.alpinelinux.org/alpine/aports/issues/7754

[chrisys]

@escoand yes, I'm absolutely interested in getting this merged! Thanks so much for sharing your work here.

I'll give it a test and review here, but in the meantime could you take a look here and update your commit message accordingly: https://github.com/balena-io-projects/balena-dash/blob/master/CONTRIBUTING.md

[escoand]

@chrisys yes, sure. So it has to be only a single commit? And what kind of commit is it? Minor?

[chrisys]

@escoand yep just one of the commits, and minor is good for this as it's a (great) new feature!

[escoand]

@chrisys the code should be ready for merge.

[escoand]

Are there open problems? Or why is the PR still pending?

[chrisys]

@escoand I tested this today finally - I couldn't get it to work on my monitor. I would prefer it if the changes leave the default behavior unchanged and add functionality; right now it looks like there's a risk of it being a breaking change as it defaults to using cec-client if the output from tvservice -s doesn't match. What are your thoughts on this? Is there a way to default to the existing method but change to cec-client if a compatible display is detected?

[escoand]

Sure, but there seem to be a lot interesting states https://www.raspberrypi.org/forums/viewtopic.php?t=52309

[escoand]

@chrisys what does tvservice -s show on your installation? And what is happening when you call the script or echo scan | cec-client -s -d 1 manually?

[ReubenBTalbott]

Is there any update on this? I would like to be able to sleep my HDMI monitor at night and all the documentation seems to say that only the RPi screen is able to do that at the moment.

[escoand]

With this PR it should work but switched to Screenly and don't use this anymore.