[Bug 76276] Backlight control broken on Dell XPS13 w/ kernel 3.14-rc7

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=76276

--- Comment #31 from Mike C <mike.cloaked at gmail.com> ---
I seem to have a corresponding issue with a Samsung Q35 laptop running arch
linux.  The screen brightness was not a problem until I updated recently to
kernel 3.14.1-1-ARCH.

The graphics hardware is

00:02.0 VGA compatible controller: Intel Corporation Mobile 945GM/GMS,
943/940GML Express Integrated Graphics Controller (rev 03)
00:02.1 Display controller: Intel Corporation Mobile 945GM/GMS/GME, 943/940GML
Express Integrated Graphics Controller (rev 03)

With the the 3.14 kernel the screen shows normal brightness during POST, and
for the initial stages of the boot. But the screen dims to an unusable level
when X starts so that the KDM login greeter screen is so dim it would be
unusable. At this stage I can use the Fn+up arrow key once and the screen goes
to full brightness.  If I then login, then the screen dims again after a short
time so that the logged in user again has a screen that is too dim to be
usable. Again pressing Fn+ up arrow restores full brightness.

There is nothing indicating a problem in the systemd journal log. There is
nothing that seems to indicate a problem in /var/log/Xorg.0.log either.

Trying to boot with acpi_video=vendor does not help. Adding in a file as per:
cat /etc/X11/xorg.conf.d/10-intel.conf 
Section "Device"
        Option     "Backlight"  "intel_backlight"
        Identifier  "Card0"
        Driver      "intel"
        BusID       "PCI:0:2:0"

also made no difference.

Attempting to use xbacklight -dec 10 after the backlight was set using the key
combination specified above then dimmed the screen to be unusable and I could
not then recover using Fn+up arrow and had to reboot. I guess restarting X may
have worked also.

I also tried 

echo 0 > /sys/class/backlight/intel_backlight/brightness but that also dimmed
the screen to be unusable and I could not then recover the brightness.

The only directory in the /sys/class/backlight is:
intel_backlight

I don't know if this problem has a potential fix coming in kernel 3.15 or
whether this is an xorg problem?

-- 
You are receiving this mail because:
You are the QA Contact for the bug.
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/intel-gfx-bugs/attachments/20140420/3427d125/attachment.html>