The SMI-based backlight control functionality may fail to work if the
system is running under EFI rather than BIOS.  Check that the hardware
responds as expected, and exit if it doesn't.
Signed-off-by: NMatthew Garrett <mjg@redhat.com>
Acked-by: NRichard Purdie <richard.purdie@linuxfoundation.org>
Cc: Mourad De Clerck <mourad@aquazul.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>