@Steve Beattie, could you also add the output of "grep -r . /proc/acpi/video" from the non-working case.
@Olivier, I am sorry to have told the wrong method. Though strange it made a difference. The module should fail to load in either case... Might I ask you to try out "acpi_backlight=video" as a kernel parameter and to remove that options entry and report whether this is ok as well? Sory again for the confusion.
@Steve Beattie, could you also add the output of "grep -r . /proc/acpi/video" from the non-working case.
@Olivier, I am sorry to have told the wrong method. Though strange it made a difference. The module should fail to load in either case... Might I ask you to try out "acpi_backlight =video" as a kernel parameter and to remove that options entry and report whether this is ok as well? Sory again for the confusion.