drm2 regression: backlight adjustment on ivybridge no longer works

Hi,

I've just found a regression.

The backlight adjustment doesn't work on my ivybridge mobile laptop
(Lenovo X230) after the dri update.

I've added debugging. It's making it all the way to the pch backlight
panel update routine in intel_panel.c, but it's not changing the
backlight appearance itself.

The "intel_backlight" program from intel-gpu-tools" also no longer
changes the backlight value.

I'm going to finish rebuilding -HEAD on the sandy bridge laptop here
and try it out.

Thanks,



-adrian