I've got a report of build failure on ideapad-laptop, which shows
drivers/built-in.o: In function `ideapad_acpi_notify':
ideapad-laptop.c:(.text+0x63876a): undefined reference to `backlight_force_update'
drivers/built-in.o: In function `ideapad_acpi_remove':
ideapad-laptop.c:(.devexit.text+0x64a7): undefined reference to `backlight_device_unregister'
drivers/built-in.o: In function `ideapad_acpi_add':
ideapad-laptop.c:(.devinit.text+0x45e28): undefined reference to `backlight_device_register'
To select backlight subsystem can prevent this error from happening.
Also update comment for this driver.
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Ike Panhc <ike.pan@canonical.com>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
        depends on RFKILL && INPUT
        depends on SERIO_I8042
        select INPUT_SPARSEKMAP
+       select BACKLIGHT_CLASS_DEVICE
        help
-         This is a driver for the rfkill switches on Lenovo IdeaPad netbooks.
+         This is a driver for Lenovo IdeaPad netbooks contains drivers for
+         rfkill switch, hotkey, fan control and backlight control.
 
 config THINKPAD_ACPI
        tristate "ThinkPad ACPI Laptop Extras"