Disable _BQC once it returns an invalid value.
http://bugzilla.kernel.org/show_bug.cgi?id=13887

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
---
 drivers/acpi/video.c |   66 +++++++++++++++++++++++++++------------------------
 1 file changed, 35 insertions(+), 31 deletions(-)

Index: linux-2.6/drivers/acpi/video.c
===================================================================
--- linux-2.6.orig/drivers/acpi/video.c
+++ linux-2.6/drivers/acpi/video.c
@@ -603,37 +603,44 @@ acpi_video_device_lcd_get_level_current(
 					unsigned long long *level)
 {
 	acpi_status status = AE_OK;
+	int state;
+	char *buf;
 
-	if (device->cap._BQC || device->cap._BCQ) {
-		char *buf = device->cap._BQC ? "_BQC" : "_BCQ";
+	*level = device->brightness->curr;
+
+	if (!device->cap._BQC && !device->cap._BCQ)
+		return 0;
 
-		status = acpi_evaluate_integer(device->dev->handle, buf,
-						NULL, level);
-		if (ACPI_SUCCESS(status)) {
-			if (device->brightness->flags._BQC_use_index) {
-				if (device->brightness->flags._BCL_reversed)
-					*level = device->brightness->count
-								 - 3 - (*level);
-				*level = device->brightness->levels[*level + 2];
+	buf = device->cap._BQC ? "_BQC" : "_BCQ";
 
+	status = acpi_evaluate_integer(device->dev->handle, buf,
+					NULL, level);
+	if (ACPI_SUCCESS(status)) {
+		if (device->brightness->flags._BQC_use_index) {
+			if (device->brightness->flags._BCL_reversed)
+				*level = device->brightness->count
+							 - 3 - (*level);
+			*level = device->brightness->levels[*level + 2];
 			}
-			*level += bqc_offset_aml_bug_workaround;
-			device->brightness->curr = *level;
-			return 0;
-		} else {
-			/* Fixme:
-			 * should we return an error or ignore this failure?
-			 * dev->brightness->curr is a cached value which stores
-			 * the correct current backlight level in most cases.
-			 * ACPI video backlight still works w/ buggy _BQC.
-			 * http://bugzilla.kernel.org/show_bug.cgi?id=12233
-			 */
-			ACPI_WARNING((AE_INFO, "Evaluating %s failed", buf));
-			device->cap._BQC = device->cap._BCQ = 0;
-		}
-	}
+		*level += bqc_offset_aml_bug_workaround;
 
-	*level = device->brightness->curr;
+		for (state = 2; state < device->brightness->count; state++)
+	                if (level == device->brightness->levels[state]) {
+				device->brightness->curr = *level;
+				return 0;
+			}
+	}
+	/* Fixme:
+	 * should we return an error or ignore this failure?
+	 * dev->brightness->curr is a cached value which stores
+	 * the correct current backlight level in most cases.
+	 * ACPI video backlight still works w/ buggy _BQC.
+	 * http://bugzilla.kernel.org/show_bug.cgi?id=12233
+	 * http://bugzilla.kernel.org/show_bug.cgi?id=13887
+	 */
+	ACPI_WARNING((AE_INFO, "Evaluating %s %s, current brightness %d\n",
+		buf, ACPI_SUCCESS(status) ? "success" : "failed", *level));
+	device->cap._BQC = device->cap._BCQ = 0;
 	return 0;
 }
 
@@ -1946,10 +1953,7 @@ static int
 acpi_video_switch_brightness(struct acpi_video_device *device, int event)
 {
 	unsigned long long level_current, level_next;
-	int result = -EINVAL;
-
-	if (!device->brightness)
-		goto out;
+	int result;
 
 	result = acpi_video_device_lcd_get_level_current(device,
 							 &level_current);
@@ -2124,7 +2128,7 @@ static void acpi_video_device_notify(acp
 	struct input_dev *input;
 	int keycode;
 
-	if (!video_device)
+	if (!video_device || !video_device->brightness)
 		return;
 
 	device = video_device->dev;