@kaxing Can you add kernel parameter to grub without the workaround you found and test the backlight function again?
Either "acpi_video=vendor" or "video.use_native_backlight=1" ** Changed in: linux-lts-trusty (Ubuntu) Status: New => In Progress -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1354313 Title: [Dell Inspiron 5721] Brightness control does not work with 12.04.5(with kernel 3.13) To manage notifications about this bug go to: https://bugs.launchpad.net/hwe-next/+bug/1354313/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs