Arch Linux

Description:
This is a crosspost to help with tracking this problem. Originally I thought this was a systemd problem:
https://bugs.freedesktop.org/show_bug.cgi?id=79159
but it turned out to be a kernel problem. I filed in the kernel bugtracker here:
https://bugzilla.kernel.org/show_bug.cgi?id=76811

Issue explained in detail in above links. An excerpt:

"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)."

Additional info:
* package version(s)
3.14.4-1 (linux) and 3.10.40 (linux-lts); also applies to 3.14.4.201405141623-1 (linux-grsec) in Community.

* config and/or log files etc.
Stock kernels

Steps to reproduce:
Have Optimus enabled, set the screen brightness to whatever, then suspend the laptop. Upon resume the screen will go to 100% brightness. Details in above links clarify why if needed.

System fully up-to-date.