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).