ACPI video: support reversed _BCL method in ACPI video driver

The brightness levels returned by _BCL package are in a reversed order
on some laptops.
http://bugzilla.kernel.org/show_bug.cgi?id=12037
http://bugzilla.kernel.org/show_bug.cgi?id=12302
http://bugzilla.kernel.org/show_bug.cgi?id=12235

sort the _BCL packge in case it's reversed.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Acked-by: Matthew Garrett <mjg59@srcf.ucam.org>
Acked-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 9 insertions, 3 deletions

diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index 398b3eee37fb..dc84970ce1e9 100644
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -170,6 +170,7 @@ struct acpi_video_device_cap {
 
 struct acpi_video_brightness_flags {
         u8 _BCL_no_ac_battery_levels:1; /* no AC/Battery levels in _BCL */
+        u8 _BCL_reversed:1;             /* _BCL package is in a reversed order*/
 };
 
 struct acpi_video_device_brightness {
@@ -744,9 +745,14 @@ acpi_video_init_brightness(struct acpi_video_device *device)
         } else if (level_ac_battery > 2)
                 ACPI_ERROR((AE_INFO, "Too many duplicates in _BCL package\n"));
 
-        /* sort all the supported brightness levels */
-        sort(&br->levels[2], count - 2, sizeof(br->levels[2]),
-                acpi_video_cmp_level, NULL);
+        /* Check if the _BCL package is in a reversed order */
+        if (max_level == br->levels[2]) {
+                br->flags._BCL_reversed = 1;
+                sort(&br->levels[2], count - 2, sizeof(br->levels[2]),
+                        acpi_video_cmp_level, NULL);
+        } else if (max_level != br->levels[count - 1])
+                ACPI_ERROR((AE_INFO,
+                            "Found unordered _BCL package\n"));
 
         br->count = count;
         device->brightness = br;