Comment 69 for bug 292256

Yes, I'm running a laptop; no, there's nothing strange about the backlight in gnome-power-manager --verbose.

KMS is involved: a better workaround for me is to use i915.modeset=0 as kernel option - no KMS, means quirks enabled, means backlight working (with Japi's fix, that is; the 2372 type should still be included in the 20-video-quirk-pm-ibm.fdi file).