Reviewing this is definitely on my list btw, sorry for the wait. Wanted to do it today, but might have to wait until tomorrow. This also somewhat conflicts with my other MR over at !306 and the branch I've got on top of it, so rebasing will be fun. (Not.)
The quick initial look I gave this looks fine and I'm very much onboard with displayAdded/displayRemoved in general, also as API that ScreenBrightness can use later. Need to have a closer look though. It would be nice if we could avoid exposing the ddcutil header to ScreenBrightness.
@littlesweet, I'm not sure how many changes are in each of your pushes, but keep in mind that you don't have to rebase & push your branch for every new commit that lands master. Once every now and then is fine, or when the patch itself changes, or when there's a new merge conflict with master.
