[Bug 97244] [SKL] 5k tiled monitor DP sync issues

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97244

--- Comment #10 from Tomas Bzatek <bugs at bzatek.net> ---
Well for the time being I managed to make it run by using the buggy BFS
scheduler (out-of-the-tree CFS process scheduler replacement) that somehow
makes the whole drm subsystem laggy. Please disregard my findings in comment 3,
it's more or less independent of Xorg settings. No luck with setting up
Xinerama either (in reply to comment 4).

My theory is that the bug causes delaying the phase the outputs are set up and
once the lag is over, it activates both outputs at the same moment. It's lame
but it's a sufficient workaround for now :-)

And when the outputs are in sync, the monitor holds the sync for a whole day,
without flickering. There are no issues with cursor or windows DP1 <-> DP2
transition either, it really feels like a single screen, even tearing is in
sync. Good work on that front.


Unfortunately I didn't have much time to debug this issue, it's still on my
TODO list though. Assigning common PLL clock source (as suggested in comment 6)
could be the way to go. I've also tried patching the kernel to delay the second
output to be in vsync with the first (as suggested by intel developers on irc),
with no luck so far.

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