Merge lp://staging/~kaihengfeng/unity-settings-daemon/add-brightness-limit-mechanism into lp://staging/unity-settings-daemon

TBH, I'm not a fan of introducing configurability for such things. It sounds too much like an "unbreak my desktop setting" and a hack for a bug, it introduces combinatorial explosion again which nobody will test properly, and it'll be hard to drop such settings again.

My opinion is not authoritative here of course, it's ultimately the desktop teams' decision.

I'm tentatively +1 on this. I agree with Martin that this is an "unbreak my system" knob but ultimately the world where I have this knob is better than the one we are in now, where desktops _are_ broken.

I would love to see an user-visible checkbox that controls if backlight turns off at 0% and a system-vendor tunable that actually controls the 0-100% span.

> I would love to see an user-visible checkbox that controls if backlight turns off at 0% and a system-vendor tunable that actually controls the 0-100% span.

Erk, please no. This is the absolutely worst UI.

Also, this high-level user space is *not* the point to second-guess/workaround kernel drivers. Userspace should use the brightness range that the kernel offers, and if there's somehting wrong with that it needs to be fixed in that driver.

I strongly agree with Martin's remarks. This should be fixed in the respective drivers. Not only because that's the conceptually correct place, but also because otherwise we'll have to hack around this in every place that brightness is controlled in user space.

> I would love to see an user-visible checkbox that controls if backlight turns off at 0% and a system-vendor tunable that actually controls the 0-100% span.

Why would anyone ever want to turn off the backlight for LCD screens? Turning down the brightness is not the same as turning off the screen.

FTR, https://code.launchpad.net/~fourdollars/unity-settings-daemon/fix-lowest-brightness/+merge/277326 addresses the same problem in an (IMHO) much better way, as it keeps the heuristics in the code (and thus changeable) without providing extra knobs.

Although I still prefer configuration for such an issue, I am happy to see this issue being addressed.

please no, I only see thing on windows devices to trick the battery life stats - setting it lower on battery vs plugged in is one thing(user can still increase to actual max), but forcing a limit that you can't turn up past unless you go into settings is a bad idea.