<html> <head> <base href="https://bugs.freedesktop.org/" /> </head> <body> <div> <a class="bz_bug_link bz_status_RESOLVED bz_closed" title="RESOLVED FIXED - [i915 intel_backlight] can't regulate brightness at GDM login prompt if HDMI monitor connected" href="https://bugs.freedesktop.org/show_bug.cgi?id=87286#c22">Comment # 22</a> on <a class="bz_bug_link bz_status_RESOLVED bz_closed" title="RESOLVED FIXED - [i915 intel_backlight] can't regulate brightness at GDM login prompt if HDMI monitor connected" href="https://bugs.freedesktop.org/show_bug.cgi?id=87286">bug 87286</a> from <a class="email" href="mailto:jre.winesim@gmail.com" title="jre.winesim@gmail.com">jre.winesim@gmail.com</a> <pre>1.) I can confirm that indeed the xserver-xorg-video-intel backlight helper fixes the issue (and not an unrelated change). If I build my own packages based on the preceding commit [1] the problem still exists. After applying the next 2 commits [2] everything works (there are some more related commits in the repo, but this is the minimal changeset). [1]: git://anonscm.debian.org/pkg-xorg/driver/xserver-xorg-video-intel commit a01548ccf192a5b1fa1f4a3e31e1634db39f6b39 intel: export fd_set_cloexec / fd_set_nonblock [2]: commit b71f3d8bd4d6773899c1bdc903911cf240e68ead Backlight helper build fixes commit 3d629c91cfa98b75c6685c2a2003e64fd1b612c4 intel: Add a helper for setting backlight without root rights 2.) I can also confirm that while the problem exists (GDM login screen black and brightness not adjustable) I can adjust the brightness with e.g.: # echo 4647 > /sys/class/backlight/intel_backlight/brightness (In reply to Aaron Lu from <a href="show_bug.cgi?id=87286#c20">comment #20</a>) > (In reply to Luca Boccassi from <a href="show_bug.cgi?id=87286#c19">comment #19</a>) > > Hello Aaron, > > > > That package ships a binary, xf86-video-intel-backlight-helper, which > > apparently is used to regulate the brightness. I'm not familiar with the > > code myself or the project itself, but with a quick Google search this Xorg > > mailer thread came up and it does shed some light on how this is used: > > <a href="http://lists.x.org/archives/xorg-devel/2014-February/040575.html">http://lists.x.org/archives/xorg-devel/2014-February/040575.html</a> > > Thanks for the pointer. The helper is used to write a value to the > /sys/class/backlight/X/brightness and the fact that it now works means that > the native interface works and the original problem may be due to broken > user space tool. If I understood it correctly, the helper is used to write a value to the /sys/class/backlight/X/brightness *with root rights*, because xf86-video-intel requires them (contrary to all other drivers). Still I don't understand why this is a problem here before login to Gnome, but not after. (I'm running a "normal" Debian Jessie here with Xorg/gdm3 running as root.) So probably yes, broken user space tool. (In reply to Aaron Lu from <a href="show_bug.cgi?id=87286#c20">comment #20</a>) > If the backlight indeed works, then we have mistakenly disabled the native > interface and I think we should revert that patch. Based on Linus "We do not break userspace" I disagree. Everything works fine here with an older kernel <3.16. And it works again for every newer kernel I tested if I disable intel_backlight. So there was a regression in the kernel which had to be fixed. Having said that the above mentioned thread (and it links) show that the complete backlight implementation would gain from a redesign coordinated between X/kernel/... . Until then IMO the ugly blacklist to disable native blacklight has to remain. Greets jre</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the QA Contact for the bug.</li> <li>You are on the CC list for the bug.</li> <li>You are the assignee for the bug.</li> </ul> </body> </html>