[Bug 76811] New: Kernel sets wrong screen brightness resuming from suspend on Optimus enabled laptop

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=76811

            Bug ID: 76811
           Summary: Kernel sets wrong screen brightness resuming from
                    suspend on Optimus enabled laptop
           Product: Drivers
           Version: 2.5
    Kernel Version: 3.14.4
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Video(DRI - Intel)
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: poeticrpm at gmail.com
                CC: intel-gfx-bugs at lists.freedesktop.org
        Regression: No

Originally, I thought this was a systemd bug. I am completely unsure what
subsection this bug should be filed against; apologies. Since Lennart
Poettering suggested against "the kernel driver", I will assume he means the
Intel driver. Feel free to move it. I am unsure whether this is a regression or
whether its never been seen. I can confirm that the problem remains on kernel
version 3.10.40 (Arch's LTS kernel), and also on Debian's current testing
kernel (3.14). 

Here is the link to the bug report filed against systemd:
https://bugs.freedesktop.org/show_bug.cgi?id=79159

I will paste the description from that bug below and Lennart's response:

"On systems with only one graphics card (or with Optimus disabled in BIOS),
systemd (note: I now realize the kernel) works correctly: whatever the screen
brightness when suspend is initiated is the screen brightness that is set upon
resuming from suspend. 

If the system has Optimus enabled however, resuming from suspend always sets
the backlight to 100%. This is because systemd (note: I now realize the kernel)
is apparently looking at the wrong device in /sys/class/backlight (the device
of the nvidia card, not the intel card which controls the backlight).

Consider the following contents of /sys/class/backlight on a system with
Optimus disabled:
$ ls /sys/class/backlight
acpi_video0  intel_backlight

Now consider the results of a system with Optimus enabled:
$ ls /sys/class/backlight
acpi_video0  acpi_video1  intel_backlight

In the second case, if I manually:
echo "50" > /sys/class/backlight/acpi_video1/brightness
the laptop will resume from suspend with 50% screen brightness (regardless of
what the brightness is actually set at).

Information:
Lenovo Thinkpad T530
EFI setup
Arch Linux (64bit) (Fully up to date as of this posting)
systemd version: 212 (or: 212-3 in the Arch repos)
lspci | grep "VGA" (Optimus enabled)
00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor
Graphics Controller (rev 09)
01:00.0 VGA compatible controller: NVIDIA Corporation GF108M [NVS 5400M] (rev
a1)


I am not sure whether this is a regression or if it has just never came up- I
only recently starting using Optimus (having disabled it via BIOS before) so..

If you need any other information, just ask :)"

Response from Lennart Poettering:
"systemd doesn't save/restore backlight settings across suspend/resume, only
across reboots, hence is not involved. AFAIK the kernel is responsible for
doing that part on its own, hence please file a bug against the kernel driver.
Thanks!"

-- 
You are receiving this mail because:
You are on the CC list for the bug.
You are the assignee for the bug.