ACPI / Video: Probe for output switch method when searching video devices.

This patch reverts one hunk of 677bd810
"ACPI video: remove output switching control", namely the removal of
probing for _DOS/_DOD when searching for video devices.

This is needed on some Fujitsu Laptops (at least S7110, P8010) for the
ACPI backlight interface to work, as an these machines, neither ROM nor
posting methods are available, and after removal of output switching,
none of the caps triggers, which prevents the backlight search from
being entered.

Tested on a Fujitsu Lifebook S7110 and Fujitsu Lifebook P8010.
This probably fixes https://bugzilla.kernel.org/show_bug.cgi?id=27312
for the people who have no entry in /sys/class/backlight.

This is the complete list of public (starting with "_") methods implemented
on the S7110, BIOS rev 1.34:

\_SB_.PCI0.GFX0._ADR
\_SB_.PCI0.GFX0._DOS
\_SB_.PCI0.GFX0._DOD
\_SB_.PCI0.GFX0.CRT._ADR
\_SB_.PCI0.GFX0.CRT._DCS
\_SB_.PCI0.GFX0.CRT._DGS
\_SB_.PCI0.GFX0.CRT._DSS
\_SB_.PCI0.GFX0.LCD._ADR
\_SB_.PCI0.GFX0.LCD._BCL
\_SB_.PCI0.GFX0.LCD._BCM
\_SB_.PCI0.GFX0.LCD._BQC
\_SB_.PCI0.GFX0.LCD._DCS
\_SB_.PCI0.GFX0.LCD._DGS
\_SB_.PCI0.GFX0.LCD._DSS
\_SB_.PCI0.GFX0.LCD._PS0
\_SB_.PCI0.GFX0.LCD._PS3
\_SB_.PCI0.GFX0.TV._ADR
\_SB_.PCI0.GFX0.TV._DCS
\_SB_.PCI0.GFX0.TV._DGS
\_SB_.PCI0.GFX0.TV._DSS
\_SB_.PCI0.GFX0.DVI._ADR
\_SB_.PCI0.GFX0.DVI._DCS
\_SB_.PCI0.GFX0.DVI._DGS
\_SB_.PCI0.GFX0.DVI._DSS
Signed-off-by: Michael Karcher <kernel@mkarcher.dialup.fu-berlin.de>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

drivers/acpi/video_detect.c

@@ -82,6 +82,11 @@ long acpi_is_video_device(struct acpi_device *device)
 	if (!device)
 		return 0;
 
+	/* Is this device able to support video switching ? */
+	if (ACPI_SUCCESS(acpi_get_handle(device->handle, "_DOD", &h_dummy)) ||
+	    ACPI_SUCCESS(acpi_get_handle(device->handle, "_DOS", &h_dummy)))
+		video_caps |= ACPI_VIDEO_OUTPUT_SWITCHING;
+
 	/* Is this device able to retrieve a video ROM ? */
 	if (ACPI_SUCCESS(acpi_get_handle(device->handle, "_ROM", &h_dummy)))
 		video_caps |= ACPI_VIDEO_ROM_AVAILABLE;