According to ACPI spec, _DOS "indicates that the system BIOS is capable of automatically switching the active display output or controlling the brightness of the LCD."
However, kernel commit b03738430c7537d5f87948e0b35d8aaf2688c6b4 works around it a while ago: commit b03738430c7537d5f87948e0b35d8aaf2688c6b4 Author: Zhang Rui <[email protected]> Date: Wed Jun 20 09:48:43 2012 +0800 ACPI video: Still use ACPI backlight control if _DOS doesn't exist This fixes a regression in 3.4-rc1 caused by commit ea9f8856bd6d4ed45885b06a338f7362cd6c60e5 (ACPI video: Harden video bus adding.) Some platforms don't have _DOS control method, but the ACPI backlight still works. We should not invoke _DOS for these platforms. https://bugzilla.kernel.org/show_bug.cgi?id=43168 Cc: Igor Murzov <[email protected]> Cc: [email protected] Signed-off-by: Zhang Rui <[email protected]> Signed-off-by: Len Brown <[email protected]> I also confirmed brightness controls (hotkey) work as expected in 12.04.03 ** Bug watch added: Linux Kernel Bug Tracker #43168 http://bugzilla.kernel.org/show_bug.cgi?id=43168 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1249978 Title: [Dell Latitude E6440] [Firmware Bug]: ACPI(PEGP) defines _DOD but not _DOS To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-lts-raring/+bug/1249978/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
