Screenbrightness drops after Grub [Solved]

[weasel]

I installed Sabayon Daily Gnome (64bit) on my Lenovo S300 (I5 Ivy Bridge, Intel HD4000 Graphics). When the kernel starts booting the screen turns black (brightness goes to zero) but the system boots just fine and i can raise the brightness with the fnkeys to normal. The system behaves just fine and after the boot the brightness settings are working just fine.
Thanks in advance

[weasel]

Xorg.log here : http://pastebin.com/kuNt2VwW

[wolfden]

You need to add something like acpi_osi=Linux to your grub line, it's a common thing with laptops.

https://wiki.archlinux.org/index.php/Backlight talks about it more

[weasel]

Hi Wolfden,

ive the solved the problem with the Arch Wiki (THX . The only thing thing is , that adding : "acpi_osi=Linux acpi_backlight=vendor" makes the backlightchange with fn-keys impossible. Only "acpi_backlight=vendor" makes the system behave correct.

Thank you, problem solved.

[weasel]

The above solution just works "partial". It leaves you with a very dark screen if you y´juse the grub tweaks mentioned.
Its related to the bug described here :https://bugzilla.kernel.org/show_bug.cgi?id=51231

ATM its better to not use acpi_backlight=vendor. Maybe it gets fixed in further Kernels.