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I have a Dell Latitude E6430 laptop, running Ubuntu 14.04, connected to a 27" Apple Cinema LED Display (which works fine). By tweaking the appledisplay kernel module a little bit, I can even get proper entries for the backlight in /sys/class/backlight and change the brightness using echo XXX > /sys/class/backlight/appledisplay/brightness.

As icing on the cake, I'd now like to have the brightness keys on the laptop (which do work for the laptop screen) also control the big display's brightness. Unfortunately, this doesn't work - I was assuming that as soon as a new backlight device is available, it's also connected to the brightness keys.

Any hints?

  • What are the tweaks you've done so far? – Bufke Feb 11 '15 at 16:33
  • Unfortunately, it seems like I can't find the patch anymore :-( But if I remember correctly, I only had to add the correct USB ID in appledisplay_table. – Florian Echtler Feb 11 '15 at 20:50
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A.F.A.I.K. there is only one device that gets affected by the brightness controls (and it is supposed to be the internal display). Which one is controlled by kernel parameters for example, when it comes to issues. A good writeup on that can be found here: http://hansdegoede.livejournal.com/13889.html

To get to what you want: I guess you can just write a simple script that sends those commands and map them to keys? You can get the key events by using evemu-record as root. If you look in that direction I am sure you can figure it out.

If you want to go the kernel way, check what options like acpi_backlight=native or acpi_backlight=vendor do. I know the latter makes a device specific entry, that is probably changeable to the one you created.

Good luck and let us know how it goes :).

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