[Bug 1987038] Re: Fix slow refresh rate when AMD GPU screen in reverse prime mode

[Kai-Heng Feng]

I enabled jammy-proposed and upgrade xserver-xorg-video-amdgpu. Made
sure Xorg was selected in GDM, then connected an external monitor which
routes to AMDGPU instead of Intel. Close the lid to make the external
monitor the single display, the refresh rate is smooth so the issue is
resolved.

I also boot up an AMD APU laptop to test the package and no regression
was found.

** Tags removed: verification-needed verification-needed-jammy
** Tags added: verification-done verification-done-jammy

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Title:
  Fix slow refresh rate when AMD GPU screen in reverse prime mode

Status in HWE Next:
  New
Status in xserver-xorg-video-amdgpu package in Ubuntu:
  Fix Released
Status in xserver-xorg-video-amdgpu source package in Focal:
  Confirmed
Status in xserver-xorg-video-amdgpu source package in Jammy:
  Fix Committed
Status in xserver-xorg-video-amdgpu source package in Kinetic:
  Fix Released

Bug description:
  [Impact]
  When AMD GPU is a GPU screen using reverse prime and its the only display, the fresh rate is very slow.

  [Fix]
  Enable present extension for GPU screen so it can be a viable CRTC to be selected.

  [Test]
  On a I+A laptop and external displays are routed to AMDGPU, disable internal display like closing lid can observe the issue.

  With the fix applied, the external display becomes very smooth.

  [Where problems could occur]
  I personally don't see why GPU screen can't use present extension, but this is Xorg so there might be some arcane reasons I didn't think of.

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