Created attachment 112311 [details] dmesg with drm.debug=0xe I've upgraded kernel from 3.8.0-33 to 3.11.0-13 (Ubuntu-baked kernels), and display brightness increased significantly. It's possible to modify gamma, but it doesn't affect *brightness* (or maybe backlight level). My HW is: Intel Core i5-4570S CPU build-in graphics, connected to flat-panel monitor via DVI-to-HDMI cable. PS. acpi_backlight=vendor does not have any effect. PPS. 3.12-rcX kernels have same issue.
Created attachment 112321 [details] acpidump
Created attachment 112331 [details] lspci -vvv
Unfortunately this is a wontfix one. We've adjusted the limited rbg range handling a bit to be more standards compliant, but unfortunately that breaks all the less standards compliant screens. You can work around this with xrandr -output HDMI1 --set "Broadcast RGB" Full Thanks for reporting this anyway and please reopen if the w/a doesn't help.
Hi Daniel, indeed my monitor has "incomplete" 6-bit IPS matrix, so it might appears by 2-bits "brighter". However, your xrandr "magic" workaround works, thanks! I think this should be documented somewhere, since working with overbrighted display is uncomfortable, and no other workaround exists. PS. Missing "-" fixed: xrandr --output HDMI1 --set "Broadcast RGB" Full