acpi_backlight_undef
if (acpi_backlight_cmdline != acpi_backlight_undef)
if (acpi_backlight_dmi != acpi_backlight_undef)
static enum acpi_backlight_type acpi_backlight_cmdline = acpi_backlight_undef;
static enum acpi_backlight_type acpi_backlight_dmi = acpi_backlight_undef;