Test with "video.use_native_backlight=1", "acpi_osi='!Windows 2012'", "acpi_backlight=vendor". None of those parameters makes backlight work.
After bisecting, the regression happens on 3.10-rc1. Before 3.10-rc1, only "intel_backlight" is registered under /sys/class/backlight/ and acpi/video.c shows "Current brightness invalid". So acpi_video won't register backlight device under /sys/class/backlight/ After 3.10-rc1, the acpi_video registers backlight device successfully. And the system will use acpi_video for backlight control. Also, it is not win8 backlight issue. The BIOS does not support win8 _OSI string according to DSDT table. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1353307 Title: [Lenovo B470e] Unable to control brightness on 12.04.5 To manage notifications about this bug go to: https://bugs.launchpad.net/hwe-next/+bug/1353307/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
