The brightness keys don't work with KMS. With the patch from https://bugzilla.kernel.org/show_bug.cgi?id=15054#c23 the keys work again but the brightness key events are emitted twice.
Created attachment 25780 [details] Output of: grep . /sys/class/input/input*/*
Created attachment 25781 [details] read-input-event output on /dev/input/event5 as requested in https://bugzilla.kernel.org/show_bug.cgi?id=15054#c32
Created attachment 25782 [details] read-input-event output on /dev/input/event6
Dell are sending the event via both the keyboard controller and ACPI. Can you attach the output of the acpidump command?
Created attachment 25801 [details] Output of acpidump
Is there any more debug data you need?
The hotkey works well in KMS mode, right? Method (_Q11, 0, NotSerialized) { Store (0x87, P80H) If (IGDS) { ^^^GFX0.BRTN (0x87) } Else { Notify (^^^P0P2.VGA.LCD, 0x87) } } notification is sent to ACPI video device only if IGDS is not set by BIOS, which seems to be true on this laptop. As IGDS stands for the IGD Opregion stuff which is supported by KMS only, I'm wondering why you want KMS disabled.
No, it doesn't work well with KMS. With kernel 2.6.34 rc7 it doesn't matter if KMS is enabled or not, the brightness key events are emitted twice.
I see, BTRN also sends notifications to the ACPI video device. So, IMO, the brightness hotkey control via ACPI works pretty well, except that there is an extra interrupt to the keyboard. sounds like a firmware problem to me. matthew, what do you think?
bug closed as this is a firmware bug that we can not fix... maybe you need some tricks to eliminate a hotkey event in user space.