When I install the
fglrx-experimental-13 driver that Steam recommends for my laptop (ATI Mobility Radeon HD 5000 Series) I have no backlight when I log in, but an external monitor works. I've tried a lot of backlight fixes suggested on the internet, but none of them seem to work.
I have also tried various other drivers including the drivers from the official AMD website, but both the beta and the stable drivers produce this error. Booting with
acpi_backlight=vendor flag (or various other flags for that matter) doesn't work either. Pressing the hardware keys to change the backlight also doesn't work.
Any ideas how to solve this issue?