What about devices that should support _DOS and don't support brightness? I've tested this on a D620 (which has the methods but does brightness through the BIOS) and the relevant dmesg diff is:
-acpivout0 at acpivideo1: TV__ -acpivout1 at acpivideo1: CRT_ -acpivout2 at acpivideo1: LCD_ -acpivout3 at acpivideo1: DVI_ This makes sense I guess because they're useless on this model, but I'm not sure about other laptops.
