[Bug 110417] regression drm-next-5.2-wip: breaks vsync of new Compton xrender backend

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110417

            Bug ID: 110417
           Summary: regression drm-next-5.2-wip: breaks vsync of new
                    Compton xrender backend
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: tempel.julian at gmail.com

Created attachment 143962
  --> https://bugs.freedesktop.org/attachment.cgi?id=143962&action=edit
xorg log showing the pageflipping issue

Either build Compton from git "next" branch or use latest 6.2 release:
https://github.com/yshui/compton

Start Compton with new xrender vsync:
compton --config /dev/null --backend=xrender --vsync --experimental-backends

Result: There is tearing at the very top of the screen, can be easily verified
by playing this juddertest video in fullscreen:
https://youtu.be/_gBBz7IMz1Y

This is a regression that was introduced in drm-next-5.2-wip.

There is no tearing when:
-using linux-mainline 5.1-rc4 or stable 5.0 kernel
-There is also no tearing when using drm-next-5.2-wip branch, but append
amdgpu.dc=0 to kernel start parameters.
-There's also no tearing when using Compton's GLX backends, which use
MESA_swap_control for vsync.

The attached xorg log testifies that there is a problem with pageflipping, as
it is flooded with
 [    14.785] Failed to get FB for flip
 [    14.785] (WW) AMDGPU(0): Page flip failed: Resource temporarily
unavailable
 [    14.785] (EE) AMDGPU(0): present flip failed


Compton's new xrender backend uses the present extension to implement vsync,
which works well apart from that amdgpu driver regression.
It doesn't make a difference if modesetting or amdgpu DDX is used.
The problem wasn't introduced recently into drm-next-5.2-wip, it probably
existed from the start of that branch or shortly after.

Programs versions used:
Compton 6.2
drm-next-5.2-wip-git ce933436e554f76a41612c257a2e6eb1eb6ac759
xorg-server-git 6975807945d12c07f00e18df7fafeff43efa0267
xf86-video-amdgpu 19.0.1
mesa-git 19.1 109912.9e0c744f07a

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