[Bug 106006] Kernel 4.16.0+ switch amdgpu.dc=1 causes screen brightness set to 1 to be dimmed by default

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=106006

            Bug ID: 106006
           Summary: Kernel 4.16.0+ switch amdgpu.dc=1 causes screen
                    brightness set to 1 to be dimmed by default
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: sass.joel at gmail.com

I'm noticing that the default screen brightness of my desktop when logged in is
set to something beneath "1" when set to "1" with amdgpu.dc=1 switch in the
kernel.

Test to get to this point:

* boot PC - (Grub screen brightness is "normal")
* Set kernel value amdgpu.dc=1 and proceed with 4.16.0+ kernel boot - (kernel
switches quiet and splash removed, brightness appears normal during boot
process)
* Lightdm display manager starts (brightness is still "normal")
* Log in to any window manager, When X starts, the desktop is immediately
darkened with what appears to be a high contrast setting. Looks like equivalent
to manual setting I can't actually discern. It's not brightness, necessarily,
but the net effect on the desktop is that everything is effectively darker.
* I've tested this with Ubuntu's Unity desktop, and gnome-flashback (compiz and
metacity), and it behaves the same.



When amdgpu.dc=0 is set, desktop appears a normal level of brightness when
logging in. It appears from the Xorg.0.log that the AMDGPU module isn't used
for X, but brightness isn't affected.

I'll include logs from amdgpu.dc=0 and amdgpu.dc=1. Let me know if you need any
other logs.

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