I have developed a PRELIMINARY TEST FIX for this problem, which is
caused by a dysfunctional ACPI _BCM backlight brightness control method
in the Dell Studio 1558 firmware (and likely the other 155x models).
The fix involves overriding the use of the _BCM method with the Intel
GPU i915 driver's opregion backlight control method. The fix will
therefore affect all i915-based systems that support the opregion method
not just Dell Studio systems. This does fix the brightness keys on the
Dell Studio 1558 and might also fix other i915 systems with backlight
brightness control problems.
A binary kernel including this PRELIMINARY TEST FIX (as well as the source
patch) is available here:
http://kernel.ubuntu.com/~kamal/i915_brightness/
To install this kernel, download the two .deb files and install them using:
sudo dpkg -i linux*kamal*.deb
Note that the test kernel also includes the fixes for LP: #553498 and
LP: #573120 (even though the acpi_backlight= boot option is not required
for the Dell Studio 155x with this kernel).
After rebooting, verify that "dmesg | grep backlight" yields the following
line, signifying that the backlight will be controlled by the i915 driver:
ACPI: ~kamal TEST acpi_set_backlight_register
Feedback to this bug report will be much appreciated, from Dell Studios
or any other i915-based systems.
--
Screen brightness control fails on Dell Studio 1558
https://bugs.launchpad.net/bugs/568611
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