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I'm using Arch Linux, but had this issue with other distributions as well: on HP Pavilion G6 laptop with Intel and Radeon graphic card.

When I modify the xorg.conf file to enable dualhead (such as: VGA1, leftOf, LVDS) using the Intel driver it works fine, except for LVDS ("laptop monitor") that had brightness set to 0 and was blank. Using media keys I could increase it and it was fine, but when it woke up from the screensaver it was blank again.

  1. Is this a graphic driver issue or an ACPI issue? Can I disable it somehow, or change the default value of the brightness? I've tried video=SVIDEO-1:d kernel parameters and some other hints from Arch Wiki, but it didn't work for me.

  2. This is irrelevant but still weird: when I make VGA1 (external monitor) primary and LVDS rightOf it, after boot I have to modify xorg.conf and change VGA1 to VGA2 for the dualhead to work. After restart it's VGA1 again and so on...

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I have a very similar issue with an Intel/nVidia laptop: the external monitor (which I set as primary) has zero brighness. If you try setting the external monitor as primary, does it get blank, or does the issue still happen to the LVDS? –  Kristóf Marussy Jan 6 '13 at 14:31
    
Kristóf, I am the author of question. First of all, thanks for replay. Your answer helped me. When I declared VGA1 as primary using Primary option and it worked fine- so thank you. This is probably not solution of problem but works for me. Relevant section of xorg.conf is here. My version of intel driver is compiled for 1.13.1, module version = 2.20.17. Also, i have tried adding sudo echo -n 3 > /sys/class/backlight/acpi_video0/brightness to .xinitrc but in vain.. If you have any questions or comments please ask, I sent this questions to some other forums –  kometonja Jan 9 '13 at 21:52
    
nope, LVDS is still blank blank after screensaver –  kometonja Jan 10 '13 at 0:34
    
I'm glad my comment has helped to at least create a work-around! It turned out that in my case the external monitor had some hardware failure that only triggered when I set it as the primary display (maybe something to do with initialization order? just a wild guess and probably not true), but a couple days ago it died completely. –  Kristóf Marussy Jan 15 '13 at 19:09
    
Anyways, you could try messing around with stuff under other stuff under /sys/class/backlight. For example, (on an Asus N53SV laptop) I have acpi_video{0,1} and intel_backlight. Whichever I tweak last overrules the rest, although I didn't have time to study the driver code and therefore I have no idea what is the technical reason for that. –  Kristóf Marussy Jan 15 '13 at 19:11
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