[Intel-gfx] Pageflipping bugs in drm-next on at least Ironlake and Ivybridge.

[Mario Kleiner]

Since i pulled the current drm-next tree i see strong flicker and visual 
corruption during pageflipping, both in my own app, but also in KDE4 and 
KDE5 Plasma with desktop composition enabled. This happens on both Intel 
HD Ironake mobile (Apple MBP 2010) and HD-4000 Ivybridge mobile (Apple 
macMini 2012).

It looks like page flips are not waiting properly for rendering to 
complete, showing partially rendered frames at flip time.

If i revert Daniel's commit that switches legacy pageflips from the old 
code path to the atomic code, all problems disappear, so apparently the 
atomic code for Intel is not quite ready at least on those parts?

In case this helps: As i was also testing DRI3/Present + PRIME on the 
hybrid graphics MBP, if i use the Intel HD as display gpu and the 
NVidia/nouveau as render offload gpu i don't get any corruption/flicker 
even with the atomic pageflip code for legacy pageflips. Iow. the path 
using dmabuf fence wait in intel_prepare_plane_fb works fine.

thanks,
-mario