Tested with the daily-live from March 6, 2015 as well as the image+updates all booting from a live USB as suggested in comment 4. The backlight error still appears in dmesg -l err.
The backlight controls work upon boot and I haven't noticed any losses of control. I haven't tracked down the reproducable pattern either. dmesg -l err [ 0.039901] Ignoring BGRT: invalid status 0 (expected 1) [ 5.666220] ACPI PCC probe failed. [ 6.927839] sd 4:0:0:0: [sdb] No Caching mode page found [ 6.927845] sd 4:0:0:0: [sdb] Assuming drive cache: write through [ 10.915216] [drm:radeon_acpi_init [radeon]] *ERROR* Cannot find a backlight controller [ 26.910993] systemd-logind[1973]: Failed to start user service: Unknown unit: user@999.service " -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xorg in Ubuntu. https://bugs.launchpad.net/bugs/1416186 Title: [drm:radeon_acpi_init] *ERROR* Cannot find a backlight controller To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1416186/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp
