Public bug reported:

after upgrading to 2.6.27-11-generic (on intrepid) changing the display
brightness stopped working on several thinkpad models (x61t, t60 and
t500 are mentioned at http://ubuntuforums.org/showthread.php?t=1054247,
i use a x61)

when i use the brightness controls the gnome-brightness-bar (or whatever
this onscreen indicator is called) pops up and reflects some change,
however the displays brightness won't change. same goes for xbacklight
or the gnome-brightness-applet.

i guess theses were the relevant changes which caused this bug: (from
http://launchpadlibrarian.net/20551423/linux_2.6.27-10.20_2.6.27-11.21.diff.gz
)

--- linux-2.6.27.orig/drivers/misc/thinkpad_acpi.c
+++ linux-2.6.27/drivers/misc/thinkpad_acpi.c
@@ -4921,16 +4921,25 @@
         */
        b = tpacpi_check_std_acpi_brightness_support();
        if (b > 0) {
-               if (thinkpad_id.vendor == PCI_VENDOR_ID_LENOVO) {
-                       printk(TPACPI_NOTICE
-                              "Lenovo BIOS switched to ACPI backlight "
-                              "control mode\n");
-               }
-               if (brightness_enable > 1) {
-                       printk(TPACPI_NOTICE
-                              "standard ACPI backlight interface "
-                              "available, not loading native one...\n");
-                       return 1;
+
+               if (acpi_video_backlight_support()) {
+                       if (brightness_enable > 1) {
+                               printk(TPACPI_NOTICE
+                                      "Standard ACPI backlight interface "
+                                      "available, not loading native one.\n");
+                               return 1;
+                       } else if (brightness_enable == 1) {
+                               printk(TPACPI_NOTICE
+                                      "Backlight control force enabled, even 
if standard "
+                                      "ACPI backlight interface is 
available\n");
+                       }
+               } else {
+                       if (brightness_enable > 1) {
+                               printk(TPACPI_NOTICE
+                                      "Standard ACPI backlight interface not "
+                                      "available, thinkpad_acpi native "
+                                      "brightness control enabled\n");
+                       }
                }
        }

ProblemType: Bug
Architecture: amd64
DistroRelease: Ubuntu 8.10
Package: linux-image-2.6.27-11-generic 2.6.27-11.27
ProcCmdLine: root=UUID=0aaf3329-a880-44fe-a562-92152a53fff0 ro 
acpi_sleep=s3_bios quiet splash locale=de_DE
ProcEnviron:
 
PATH=/home/username/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
 LANG=de_AT.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.27-11.27-generic
SourcePackage: linux

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: apport-bug

-- 
brightness control stopped working after update to linux-2.6.27-11-generic 
kernel
https://bugs.launchpad.net/bugs/325491
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