https://bugs.freedesktop.org/show_bug.cgi?id=94689

Bug ID: 94689 Summary: Two monitor DisplayPort MST DaisyChain (Second/Last Monitor In Chain Black Screen) Product: DRI Version: XOrg git Hardware: x86-64 (AMD64) OS: Linux (All) Status: NEW Severity: major Priority: medium Component: DRM/Radeon Assignee: dri-devel@lists.freedesktop.org Reporter: mike.ennen@gmail.com

As per our chat in #radeon (I am brcolow).

Here is the dmesg with dri.debug=6:

https://gist.github.com/brcolow/e27a5e46b175dd0966af

Here is /sys/kernel/debug/dri/0/radeon_mst_info contents:

mst: ffff88061cedfb40, 0 port: 1: ddps: 1 ldps: 0, sdp: 1/1, ffff8800bb193000, conn: ffff880622b27000 port: 8: ddps: 1 ldps: 0, sdp: 1/1, ffff8800bb192800, conn: ffff880622049000 port: 0: ddps: 1 ldps: 0, sdp: 0/0, ffff8800bb192000, conn: (null) vcpi: 7 3 vcpi 0: 8 1 22 vcpi 1: 1 2 22 vcpi 2:unsed vcpi 3:unsed vcpi 4:unsed vcpi 5:unsed payload 0: 2, 1, 22 payload 1: 2, 23, 22 payload 2: 0, 45, 0 payload 3: 0, 45, 0 payload 4: 0, 45, 0 payload 5: 0, 45, 0 dpcd: 12 14 c4 01 01 01 01 81 02 00 06 00 00 00 00 faux/mst: 00 01 mst ctrl: 07 branch oui: 00e04c devid: Dp1.2 revision: hw: 0.0 sw: 0.0 payload table: 07 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 attrib 0: 4 22 attrib 1: 2 22

The two monitors that are being daisy-chained are Dell UltraSharp U2715H's. GPU is Radeon R9 290.

I have tried doing:

xrandr --output DisplayPort-0-1 --rate X

where X = 59.9, 60, 49.9, 50, 39.9, 40 etc but it doesn't seem to change anything (and this is the extent of my debugging abilities).