Comment 20 for bug 1808183

Seems like this commit fixes the issue:
commit 5478ad10e7850ce3d8b7056db05ddfa3c9ddad9a
Author: Thomas Zimmermann <email address hidden>
Date: Thu Nov 15 11:42:16 2018 +0100

    drm/ast: Remove existing framebuffers before loading driver

    If vesafb attaches to the AST device, it configures the framebuffer memory
    for uncached access by default. When ast.ko later tries to attach itself to
    the device, it wants to use write-combining on the framebuffer memory, but
    vesefb's existing configuration for uncached access takes precedence. This
    results in reduced performance.

    Removing the framebuffer's configuration before loding the AST driver fixes
    the problem. Other DRM drivers already contain equivalent code.

    Link: https://bugzilla.opensuse.org/show_bug.cgi?id=1112963
    Signed-off-by: Thomas Zimmermann <email address hidden>
    Cc: <email address hidden>
    Tested-by: Y.C. Chen <email address hidden>
    Reviewed-by: Jean Delvare <email address hidden>
    Tested-by: Jean Delvare <email address hidden>
    Signed-off-by: Dave Airlie <email address hidden>

I built a kernel [1] with the commit, please test it.

[1] https://people.canonical.com/~khfeng/lp1808183/