Display artifacts when using MST

Submitted by Dan Doel

Assigned to Default DRI bug account

Link to original bug (#92977)

Description

Created attachment 119730
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@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.

Attachment 119730, "image 1 - half of window uses different colors":