ACPI video: work-around BIOS AML bug in _BQC

_BQC on some laptops returns an uninitialized value when it's
invoked for the first time.

Set the laptop to the maximum backlight level in this case.
http://bugzilla.kernel.org/attachment.cgi?id=22675

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 14 insertions, 4 deletions

diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index a8432c291f4..097f24c87d8 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -878,7 +878,7 @@ 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 = level_old = max_level;
+        br->curr = level = max_level;
 
         if (!device->cap._BQC)
                 goto set_level;
@@ -900,15 +900,25 @@ acpi_video_init_brightness(struct acpi_video_device *device)
 
         br->flags._BQC_use_index = (level == max_level ? 0 : 1);
 
-        if (!br->flags._BQC_use_index)
+        if (!br->flags._BQC_use_index) {
+                /*
+                 * Set the backlight to the initial state.
+                 * On some buggy laptops, _BQC returns an uninitialized value
+                 * when invoked for the first time, i.e. level_old is invalid.
+                 * set the backlight to max_level in this case
+                 */
+                for (i = 2; i < br->count; i++)
+                        if (level_old == br->levels[i])
+                                level = level_old;
                 goto set_level;
+        }
 
         if (br->flags._BCL_reversed)
                 level_old = (br->count - 1) - level_old;
-        level_old = br->levels[level_old];
+        level = br->levels[level_old];
 
 set_level:
-        result = acpi_video_device_lcd_set_level(device, level_old);
+        result = acpi_video_device_lcd_set_level(device, level);
         if (result)
                 goto out_free_levels;