On Sat, 2015-02-28 at 11:17 -0300, Henrique de Moraes Holschuh wrote: > On Sun, 22 Feb 2015, Georges Giralt wrote: > > I own a brand new Lenovo E540 (20C600JHFR) fitted with a full HD LCD > > screen. > > > > I've installed Ubuntu 14.04 LTS and exploring the syslog file for > > unsupported hardware I've found the following message : > > ======== > > thinkpad_acpi: Unsupported brightness interface, please contact > > ibm-acpi-devel@xxxxxxxxxxxxxxxxxxxxx > > [ 11.725474] thinkpad_acpi: This ThinkPad has standard ACPI backlight > > brightness control, supported by the ACPI video driver > > [ 11.725476] thinkpad_acpi: Disabling thinkpad-acpi brightness events > > by default... > > ======== > > > > I noticed that the brightness control is very coarse instead of the > > smooth control experienced in Windows > > How could I help ? > > The brightness control is done by the gpu on just about every laptop > nowadays, so you should talk to the people behind the gpu drivers and x.org. > Hello! I am one of these people :). The problem probably lies in the fact you're using Ubuntu LTS, specifically the fact it's using an older Linux kernel. Backlights changed a LOT with Windows 8 laptops. Originally we used to control it via ACPI, but now like Henrique said it is done by the GPU. In the past kernel versions this caused a lot of issues some applications try to use the ACPI backlight control over the GPU backlight, and many times the ACPI backlight control is at best, broken, on Windows 8 laptops. It's supposed to be up to the kernel to hide the ACPI backlight interface on such laptops. We used to try to maintain a list of devices in order to do this, but this turned out to be a huge hassle. Eventually the kernel guys came up with a better way to do this, but I don't exactly remember what that way was (but it does work thankfully :) There's a couple of solutions to fix the backlight control on this, although it *may* cause your backlight settings to be reset upon reboot. I do warn you I might be wrong with some of these, it's been a while since I've dealt with this problem but I'm pretty sure these are the solutions for it. The best solution next to using a newer kernel is adding: video.use_native_backlight=1 to the kernel command line. If your kernel doesn't support that, can try acpi_osi="!Windows 2012" The above solution can lead to a couple of other things breaking, or unbreaking. Generally it's one you want to avoid since having to specify an acpi OSI is generally considered a bug (ACPI should be the same across operating systems). The original bug discussing this issue can be found here: https://bugzilla.kernel.org/show_bug.cgi?id=51231 let me know if you have any questions. Cheers, Lyude
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