ACPI: video: Fix reversed brightness behavior on ThinkPad SL series

commit 935e5f290ec1eb0f1c15004421f5fd3154380fd5 upstream.

Section B.6.2 of ACPI 3.0b specification that defines _BCL method
doesn't require the brightness levels returned to be sorted.
At least ThinkPad SL300 (and probably all IdeaPads) returns the
array reversed (i.e. bightest levels have lowest indexes), which
causes the brightness management behave in completely reversed
manner on these machines (brightness increases when the laptop is
idle, while the display dims when used).

Sorting the array by brightness level values after reading the list
fixes the issue.

http://bugzilla.kernel.org/show_bug.cgi?id=12037

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Tested-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
index 111cb3d1b2e4920326151325d406586615acd507..a953b5d202985bb0d6774b33b63e8df5091b1ff7 100644 (file)
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -36,6 +36,7 @@
 #include <linux/backlight.h>
 #include <linux/thermal.h>
 #include <linux/video_output.h>
+#include <linux/sort.h>
 #include <asm/uaccess.h>
 
 #include <acpi/acpi_bus.h>
@@ -631,6 +632,16 @@ acpi_video_bus_DOS(struct acpi_video_bus *video, int bios_flag, int lcd_flag)
        return status;
 }
 
+/*
+ * Simple comparison function used to sort backlight levels.
+ */
+
+static int
+acpi_video_cmp_level(const void *a, const void *b)
+{
+       return *(int *)a - *(int *)b;
+}
+
 /*
  *  Arg:       
  *     device  : video output device (LCD, CRT, ..)
@@ -682,6 +693,10 @@ acpi_video_init_brightness(struct acpi_video_device *device)
                count++;
        }
 
+       /* don't sort the first two brightness levels */
+       sort(&br->levels[2], count - 2, sizeof(br->levels[2]),
+               acpi_video_cmp_level, NULL);
+
        if (count < 2)
                goto out_free_levels;