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

[Hans de Goede]

Hi,

On 05-09-18 20:35, Daniel Stone wrote:
> Hi Hans,
> 
> On Wed, 5 Sep 2018 at 19:23, Hans de Goede <hdegoede at redhat.com> wrote:
>> 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.
> 
> It's caused by support for modifiers: this allows Mesa to use a
> multi-planar framebuffer (auxiliary compression plane), which the new
> X server can't then read back from because drmModeGetFB only supports
> a single plane.

I do not think that that is the problem in my case. I'm seeing this
when transitioning from a GDM greeter session which is GNOME shell
as Wayland compositor to a GNOME3 on Xorg user session.

And replacing the DDX driver in the *user* session with the intel
ddx fixes this. So I think this is another issue.

Regards,

Hans