[Nouveau] [Bug 97511] New: GM204/modesetting DDX: Using PageFlip causes syncing issue/screen corruption

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97511

            Bug ID: 97511
           Summary: GM204/modesetting DDX: Using PageFlip causes syncing
                    issue/screen corruption
           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: freedesktop-bugs at theblob.org
        QA Contact: xorg-team at lists.x.org

Created attachment 126073
  --> https://bugs.freedesktop.org/attachment.cgi?id=126073&action=edit
Screenshot showing the issue on Mumble and Audacious

After working around bug #94990 so that I can use kernel modesetting, I find
that when I run a Qt application inside my regular desktop environment,
Enlightenment E20 (0.20.5) in Xorg server 1.18.4, I get issues with screen
updates, resulting in artifacts such as shown in the attached screenshot. It
appears to have issues switching between the current state and a previously
drawn state.

The issue does not appear in any non-Qt applications as far as I can tell. Note
that in the attached screenshot, Mumble is a Qt4 app and Audacious is a Qt5 app
(here running using the Winamp Classic interface). Only some Qt widgets appear
to be affected; so far I've only encountered the issue with menus, graphical
tab bars (such as the one Audacious uses in its preferences window), toolbars,
and however Audacious renders the scrolling text in its Winamp Classic
interface.

After talking with a nouveau dev on IRC (karolherbst), we determined that the
issue does not appear when the PageFlip option is set to 0 in an xorg.conf.d
file. (I will attach the configuration file I use to this bug.) I also managed
to determine that the corruption does not appear when I use another window
manager without a compositor, such as mwm. Interestingly, the corruption does
not reappear if I use mwm together with compton, a standalone compositor.

This bug only started happening after updating to Xorg server version 1.18.4
from 1.17.4. I have not as yet tested any of the previous 1.18.x releases; if
this is desired, please let me know.

Summary of system:

* Gentoo Linux, amd64, fully up-to-date, using x11 overlay
* NVidia GeForce GTX 970 (GM204)
* Kernel version 4.7.0 (with a modification to bypass bug #94990)
* Xorg server 1.18.4
* Mesa 12.0.1
* Enlightenment 0.20.5
* Qt versions installed: 4.8.6 and 5.6.1.
* Examples of Qt applications tested: Mumble (1.2.16), Audacious (3.7.1), VLC
(2.2.4), Wireshark (2.0.5).

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