[Bug 110671] Regression: DP outputs out of sync on dual-DP tiled 5k screen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110671

            Bug ID: 110671
           Summary: Regression: DP outputs out of sync on dual-DP tiled 5k
                    screen
           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: bugs at bzatek.net

With kernel 5.1.1 I get corrupted image on my Dell UP2715K screen (again). The
symptomps are similar to the ones in bug 98461 (see also attachment 127570). In
my theory this is caused by the two DisplayPort outputs not being in sync - the
screen needs both tiles to be in sync (i.e. scanlines to match) to make a
composite final image.

The Dell UP2715K monitor has two DP 1.2 inputs, two tiles expecting
2560x2880 at 60Hz modes (as exposed in EDID/DisplayInfo data). Connected to Radeon
Pro WX2100 (Polaris 12).

This used to be actually working reliably in kernel 4.20.0, yesterday I fired
up kernel 5.1.1 and only got garbage on my screen. Also tested drm-tip kernel
that includes drm-next-5.2 branch from the agd5f repo
(https://patchwork.freedesktop.org/patch/304430/) - same issue.

I haven't got time to bisect the change yet, I was hoping you could point me to
a possible commit that broke this. By any chance, do you AMD guys have a 5k
tiled screen inhouse for testing?

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