Smooth gdm -> GNOME3 session transition broken with 1.20 modesetting driver

[Hans de Goede]

Hi All,

Under Fedora 29 (xserver-1.20) the transition from GDM to
the GNOME3 session is no longer smooth, it seems that the
screen is cleared to black when the Xserver starts instead
of inheriting the framebuffer contents from GDM as before.

Changing the DDX driver from modesetting to intel fixes this,
I think this may be caused by the new atomic support in the
modesetting driver.

Note if you try to reproduce this on Fedora 29 recent
gdm versions also have some issues (*) which cause the
transition to be non smooth it is best to downgrade
gdm to 3.28.x (from koji) and then try with the intel
ddx vs the modesetting ddx to clearly see the difference.

Regards,

Hans



*) These are mostly fixed, but not entirely yet, see:
https://gitlab.gnome.org/GNOME/gdm/merge_requests/45