Nathaniel: You did try to change the brightness before collecting dmesg,
and it did not change the brightness? I'm not seeing the errors I
expected, though I'm confident they should occur because they happen
when I load your ACPI tables into a debugger.

Maybe try poking some brightness values into the driver directly and see
if you get any new messages at the bottom of dmesg. To do this, you'll
first want to run 'cat /sys/class/backlight/acpi_video0/max_brightness'.
This should output something like 101; if you get something much lower
than that (like 15) then you still have acpi_osi="!Windows 2012" applied
somehow.

Valid brightness values are anything from 0 to the value you get from
the cat command. You set a value by running 'echo n >
/sys/class/backlight/acpi_video0/brightness' as root, where n is a valid
brightness value. Just be careful of going too low, you still want to be
able to read the screen!

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https://bugs.launchpad.net/bugs/1098216

Title:
  Regression in brightness control on Lenovo Thinkpad X230 and X1 Carbon

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