Comment 5 for bug 1289748

Here's a DSDT with some debug lines in and the resulting dmesg. You can see all the values from _SB.PCI0.LPCB.EC.B* are 0, except BST0 == 2 (AC connected, 1 otherwise - at 72s I unplugged the AC, which eventually dims the backlight; at 86s I plugged AC back in and increased backlight).