[Nouveau] [Bug 97066] New: Blank screen when starting KMS on a GTX970 for kernel 4.6 series

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97066

            Bug ID: 97066
           Summary: Blank screen when starting KMS on a GTX970 for kernel
                    4.6 series
           Product: xorg
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/nouveau
          Assignee: nouveau at lists.freedesktop.org
          Reporter: pil.smmilut at yandex.com
        QA Contact: xorg-team at lists.x.org

Created attachment 125292
  --> https://bugs.freedesktop.org/attachment.cgi?id=125292&action=edit
full dmesg when experiencing the bug, and with drm.debug=14 log_buf_len=16M

Hello,

Since i upgraded my kernel from 4.5.4 to 4.6.3, the screen goes "blank" when
entering KMS, instead of giving the high resolution tty.
By "blank", i mean it has a uniform colour : during some boots it's pure red,
other boots it's pure magenta, and sometimes pure white.
The system is functional and i am able to ssh remotely into the machine.

My setup :
- single 2560x1440 monitor
- NVIDIA Corporation GM204 [GeForce GTX 970] (rev a1) (prog-if 00 [VGA
controller])
- both DVI and DisplayPort ports exhibit the issue
- Arch Linux

If i disable modesetting, i am able to see an image on the screen (low
resolution tty) and login to the system (no Xorg though, as expected).

I found bug 94990 which seems similar, although the symptoms are a bit
different (his monitor goes to sleep, mine remains ON and monochromatic). Also,
i have a similar motherboard (Z97-A).

So i tried one advice i saw there : booting with nouveau.config=NvForcePost=1
got me no signal instead of a uniform colour.

Sorry if i'm actually posting a duplicate, i'm not very experienced with this
:) I'll try provide more info if i can.

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