I'm on a Dell XPS 13 running Archlinux with Intel chipset ad Intel Graphics HD 4000 video card. With kernel versions <= 3.8.4, all backlight controls work properly: the slider in the battery plasma widget, hot keys on the keyboard and also echoing directly into /sys/class/backlight/acpi_video0/... If I update to a version >= 3.8.5 [tested up to 3.8.8] backlight goes crazy and sets brightness to 100% at startup; moreover, none of the mentioned controls will work and thus it will be impossible to reduce brightness. The other day, a strange thing happened: I was in the described situation and was trying to manually set the brightness with echo. Now, in my /sys/class/backlight/ there are two directories, acpi_video0 and intel_backlight. I tried to echo a value into intel_backlight/brightness and the screen started flashing, as if it was trying to repeatedly update both the value in acpi_video0 and the one in intel_backlight. After a couple more echoes, backlight controls [all of them] simply started working properly, until the following reboot. I didn't try to reproduce this last episode.
There is no code change in acpi video driver from 3.8.4 to 3.8.5. The following commit from graphics driver looks suspicious: 0e7a2fe01333f72c1cec1cd4d5293a62c770fa4f, can you please revert that commit and test? Thanks.
Ehm.... I'm sorry but I'm not sure how to do this :) Which repository should I clone? Is there a guide somewhere?
I have an update! I found out that, with one of the "problematic" kernels - I'm on 3.8.10 right now -, if I do $ su $ echo 0 > /sys/class/backlight/intel_backlight/brightness it completely restores correct behavior, i.e. plasma widget and special keys work and brightness can be adjusted. The problem is still present on following boots. Oddly, if I do $ sudo echo 0 > /sys/class/backlight/intel_backlight/brightness it says bash: /sys/class/backlight/intel_backlight/brightness: access denied. A friend suggested this could be a kernel bug, and may be the key to the solution. Is this any helpful?
Hi, Sorry for the late reply. Please follow the below steps: 1 clone linux stable git tree $ git clone http://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git 2 checkout 3.8 branch $ git checkout linux-3.8.y 3 set local tree to commit 5016d9ac0938789e7aaba86be3e6fbf24e7b7bee $ git reset --hard 5016d9ac0938789e7aaba86be3e6fbf24e7b7bee then build kernel and see if everything works OK 4 if yes, set local tree to commit 0e7a2fe01333f72c1cec1cd4d5293a62c770fa4f $ git reset --hard 0e7a2fe01333f72c1cec1cd4d5293a62c770fa4f then build kernel again and see if everything works OK. Thanks.
Ok,.... I'm not very used to compiling the kernel, so I'm finding it somewhat difficult: when I try make menuconfig, it asks me a lot of questions I don't know how to answer :)
I think you can use your installed kernel's config file. $ cd linux_git_tree_you_have_cloned $ cp /boot/config-3.8.4 .config $ make oldconfig Then build kernel.
You are very kind helping me like this :) However, I have no /boot/config-3.8.4 file [I use GRUB2, I think].
Attach the following command output as root: # lspci -v > lspci.out Then I can provide the config file for you to use.
Created attachment 100811 [details] lspci -v output Here it is :)
P.s. Can I compile the kernel on a different machine and then install the package on this one? I have a desktop which can compile faster and on a HDD [I have an SSD on this one].
Hi, I've built the kernel for you. No initrd is required, so your root= command line will need to use /dev/sda? instead of UUID=. URL here, since bugzilla doesn't allow upload a file more than 1000KB: https://www.dropbox.com/s/sgxikmdkzmhhjzp/vmlinuz-bad https://www.dropbox.com/s/u6e1qfoktenynlr/vmlinuz-good
Ok, I did some testing and here's the result. I took each of the files you shared and copied them into /boot/vmlinuz-linux, then rebooted. With vmlinuz-good, backlight controls worked; with vmlinuz-bad, they didn't, so I guess you found the core of the problem! [Maybe unnecessary to tell, with both of them I had some issues like networkmanager and kmix not working, but I think this is because you compiled it away from my hardware] Did I do well? Is there anything else I can do? :) Thanks a lot for your support!
Thanks for the test, I'll move this bug to drm/intel category and I think they know what happened. Hi DRM guys, Looks like the following commit: commit 0e7a2fe01333f72c1cec1cd4d5293a62c770fa4f Author: Daniel Vetter <daniel.vetter@ffwll.ch> Date: Fri Mar 22 15:44:46 2013 +0100 Revert "drm/i915: write backlight harder" breaks backlight functionality of leoni's system, please kindly take a look, thanks.
Awesome, I love the way bugreporting works :) Thank you all for this!
The original commit "drm/i915: write backlight harder" fixed the issue on Dell XPS 13, but unfortunately it regressed other machines and had to be reverted. *** This bug has been marked as a duplicate of bug 47941 ***