The QXL DRM driver as a reminder is for Red Hat's SPICE with guest virtual machines on QEMU. QXL -- presumably with Linux 4.12 -- will join Nouveau, Intel, and other DRM drivers in supporting atomic mode-setting.
The QXL atomic mode-setting has been tested so far with the X.Org Server, the IGT tests, libdrm's test suite, and other custom tests.
Adding atomic mode-setting to the QXL driver was 434 lines of new code but 449 lines of deleted code. More details via this patch series.