ACPI video: handle indexed _BQC correctly

In the current code, for a box with an indexed _BQC method, we
1. get the current brightness level by evaluating _BQC
2. set the value gotten in step 1 to _BCM
3. get the current brightness level again
4. set the _BQC_use_index flag if the results gotten
   in step 1 and in step 3 don't equal.

But this logic doesn't work actually, because the _BQC_use_index
is not set when acpi_video_device_lcd_set_level is invoked.
This results in a failure in step 2.
http://bugzilla.kernel.org/show_bug.cgi?id=12249#c83

Now, we set the _BQC_use_index flag after invoking _BQC for the first
time. And reevaluate the _BQC to get the correct brightness level.
Signed-off-by: NZhang Rui <rui.zhang@intel.com>
Signed-off-by: NLen Brown <len.brown@intel.com>

drivers/acpi/video.c

@@ -807,12 +807,19 @@ acpi_video_init_brightness(struct acpi_video_device *device)
 	br->flags._BCM_use_index = br->flags._BCL_use_index;
 
 	/* _BQC uses INDEX while _BCL uses VALUE in some laptops */
-	br->curr = max_level;
+	br->curr = level_old = max_level;
+
+	if (!device->cap._BQC)
+		goto set_level;
+
 	result = acpi_video_device_lcd_get_level_current(device, &level_old);
 	if (result)
 		goto out_free_levels;
 
-	result = acpi_video_device_lcd_set_level(device, br->curr);
+	/*
+	 * Set the level to maximum and check if _BQC uses indexed value
+	 */
+	result = acpi_video_device_lcd_set_level(device, max_level);
 	if (result)
 		goto out_free_levels;
 
@@ -820,25 +827,19 @@ acpi_video_init_brightness(struct acpi_video_device *device)
 	if (result)
 		goto out_free_levels;
 
-	if ((level != level_old) && !br->flags._BCM_use_index) {
-		/* Note:
-		 * This piece of code does not work correctly if the current
-		 * brightness levels is 0.
-		 * But I guess boxes that boot with such a dark screen are rare
-		 * and no more code is needed to cover this specifial case.
-		 */
-
-		if (level_ac_battery != 2) {
-			/*
-			 * For now, we don't support the _BCL like this:
-			 * 16, 15, 0, 1, 2, 3, ..., 14, 15, 16
-			 * because we may mess up the index returned by _BQC.
-			 * Plus: we have not got a box like this.
-			 */
-			ACPI_ERROR((AE_INFO, "_BCL not supported\n"));
-		}
-		br->flags._BQC_use_index = 1;
-	}
+	br->flags._BQC_use_index = (level == max_level ? 0 : 1);
+
+	if (!br->flags._BQC_use_index)
+		goto set_level;
+
+	if (br->flags._BCL_reversed)
+		level_old = (br->count - 1) - level_old;
+	level_old = br->levels[level_old];
+
+set_level:
+	result = acpi_video_device_lcd_set_level(device, level_old);
+	if (result)
+		goto out_free_levels;
 
 	ACPI_DEBUG_PRINT((ACPI_DB_INFO,
 			  "found %d brightness levels\n", count - 2));