Comment 5 for bug 1295141

Aaron Lu asked for these things:

Please list what backlight control interfaces do you have:
# ls /sys/class/backlight
acpi_video0 intel_backlight

And test if manually echo a value works:
# cd /sys/class/backlight/i915_xxx
# cat max_brightness

user@Qosmio-X75-A:~$ cd /sys/class/backlight/i915_xxx
bash: cd: /sys/class/backlight/i915_xxx: No such file or directory
user@Qosmio-X75-A:~$ cd /sys
user@Qosmio-X75-A:/sys$ ls
block class devices fs kernel power
bus dev firmware hypervisor module
user@Qosmio-X75-A:/sys$ cd class/backlight/
user@Qosmio-X75-A:/sys/class/backlight$ ls
acpi_video0 intel_backlight
user@Qosmio-X75-A:/sys/class/backlight$ cd intel_backlight
user@Qosmio-X75-A:/sys/class/backlight/intel_backlight$ ls
actual_brightness brightness max_brightness subsystem uevent
bl_power device power type
user@Qosmio-X75-A:/sys/class/backlight/intel_backlight$ cat max_brightness
5273
user@Qosmio-X75-A:/sys/class/backlight/intel_backlight$ cd ..
user@Qosmio-X75-A:/sys/class/backlight$ ls
acpi_video0 intel_backlight
user@Qosmio-X75-A:/sys/class/backlight$ cd acpi_video0
user@Qosmio-X75-A:/sys/class/backlight/acpi_video0$ ls
actual_brightness brightness max_brightness subsystem uevent
bl_power device power type
user@Qosmio-X75-A:/sys/class/backlight/acpi_video0$ cat max_brightness
100
user@Qosmio-X75-A:/sys/class/backlight/acpi_video0$ echo 400 > brightness
bash: brightness: Permission denied
user@Qosmio-X75-A:/sys/class/backlight/acpi_video0$ sudo echo 400 > brightness
bash: brightness: Permission denied
user@Qosmio-X75-A:/sys/class/backlight/acpi_video0$ cd ..
user@Qosmio-X75-A:/sys/class/backlight$ ls
acpi_video0 intel_backlight
user@Qosmio-X75-A:/sys/class/backlight$ cd intel_backlight
user@Qosmio-X75-A:/sys/class/backlight/intel_backlight$ ls
actual_brightness brightness max_brightness subsystem uevent
bl_power device power type
user@Qosmio-X75-A:/sys/class/backlight/intel_backlight$ cat brightness
5100
user@Qosmio-X75-A:/sys/class/backlight/intel_backlight$ sudo echo 400 > brightness
bash: brightness: Permission denied
user@Qosmio-X75-A:/sys/class/backlight/intel_backlight$ sudo echo 600 > brightness
bash: brightness: Permission denied

(see attachment of acpidump.txt)