[Bug 92977] Display artifacts when using MST

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=92977

            Bug ID: 92977
           Summary: Display artifacts when using MST
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Radeon
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: dan.doel at gmail.com

Created attachment 119730
  --> https://bugs.freedesktop.org/attachment.cgi?id=119730&action=edit
image 1 - half of window uses different colors

I've been trying out the support for tiled MST monitors on Radeon drivers, and
seem to be encountering some visual anomalies that seem like they are likely to
be related to this component.

My setup is two UP2414Q monitors, which have native resolutions of 3840x2160.
Over DisplayPort 1.2, they are capable of running as two 1920x2160 at 60 displays
each. I have a nvidia card that is capable of driving them in this mode, so I
am reasonably sure that the hardware isn't the problem (unless it is the Radeon
card, but that seems unlikely).

First, there seems to be a color anomaly with the primary display. The right
half of the display has different colors from the left (see first image). I
noticed that this may be due to the left half displaying a different color
depth than the right. The second image shows the gnome overlay, and while the
shadows are smooth on the right, there is banding on the left. My second
monitor seems to have both sides in this reduced color mode, and enough
fiddling with settings after a boot causes both halves of the primary monitor
to be configured that way as well, but needless to say, the reduced color depth
(if that's what it is) is undesirable.

Second, the secondary monitor has some visual artifacts to the left of center
(a vertical band about an inch wide) as well as to the far right (a vertical
band around 1/4 inch wide). The third image should give some idea what it looks
like. A better photo might show that things in that region look somewhat
interlaced, and are repeated horizontally.

I apologize for the poor quality of the images, but screenshots don't capture
these artifacts, so I had to use my phone.

I'm running with packages from Fedora 23, so xorg-server 1.18.0, xf86-video-ati
7.6.0-0.4.20150729git5510cd6, kernel 4.2.5-300. If you'd like any other
information, let me know.

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