https://bugs.freedesktop.org/show_bug.cgi?id=81382
--- Comment #8 from Daniel Kirsten daniel-kirsten-72@excite.com --- The above patch causes a problem on my Amilo Xi 2550 (RadeonHD 2600).
The behaviour for kernel-3.14.8-100.fc19 (without patch):
The value of /sys/class/backlight/radeon_bl0/brightness is 0. Whenever I write something (0-255) to /sys/class/backlight/radeon_bl0/brightness, the backlight is turned off, and I am not able to turn on the backlight again. However, I can still shutdown the system (Ctr+Alt+Fx, login as root, and give a shutdown command.
I can control the backlight by writing values 0-7 to /sys/class/backlight/acpi_video0/brightness.
The behaviour for kernel-3.14.17-100.fc19 (with patch):
The backlight is turned off during the boot up process, when the kernel switches into graphics mode. I commented out the lines 233-234 in drivers/gpu/drm/radeon/atombios_encoders.c, and then, the problem disappeared, i.e., the backlight stays on when the kernel switches into graphics mode.
Best regards, Daniel