ACPI / video: check _DOD list when creating backlight devices

The _DOD method lists which video output device is currently attached so
we should only care about them and ignore others. An user recently
reported that there are two acpi_video interfaces appeared on his system
and one of them doesn't work. From the acpidump, it is found that there
are more than one video output devices that have _BCM control method but
the _DOD lists only one of them. So this patch checks if the video output
device is in the _DOD list and will not create backlight device if it is
not in the list. Also, we consider the broken _DOD case(reflected by the
video->attached_count is 0) and do not change behaviour for those broken
_DOD systems.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=84111
Reported-and-tested-by: ntrrgc@gmail.com
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/video.c

@@ -1146,6 +1146,23 @@ acpi_video_device_bind(struct acpi_video_bus *video,
 	}
 }
 
+static bool acpi_video_device_in_dod(struct acpi_video_device *device)
+{
+	struct acpi_video_bus *video = device->video;
+	int i;
+
+	/* If we have a broken _DOD, no need to test */
+	if (!video->attached_count)
+		return true;
+
+	for (i = 0; i < video->attached_count; i++) {
+		if (video->attached_array[i].bind_info == device)
+			return true;
+	}
+
+	return false;
+}
+
 /*
  *  Arg:
  *	video	: video bus device
@@ -1585,6 +1602,15 @@ static void acpi_video_dev_register_backlight(struct acpi_video_device *device)
 	static int count;
 	char *name;
 
+	/*
+	 * Do not create backlight device for video output
+	 * device that is not in the enumerated list.
+	 */
+	if (!acpi_video_device_in_dod(device)) {
+		dev_dbg(&device->dev->dev, "not in _DOD list, ignore\n");
+		return;
+	}
+
 	result = acpi_video_init_brightness(device);
 	if (result)
 		return;