Comment 35 for bug 1229591

Chris Stratford, thank you for your quick response. Could you please clear out the non-default kernel boot parameters, and test the following individually and advise if it changes anything:
acpi_backlight=vendor
video.use_bios_initial_backlight=0

when only testing a mainline kernel v3.13.x+ (for example http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.13-rc6-trusty/ ):
video.use_native_backlight=1