X displays normally with this patch set (as amended) applied to Linux 4.19.1
commit 07a03b97b9ce2a6430344386eeab9b16283b893f on branch linux-4.19.y of the
stable tree.
There was an oddity the first time I tried it which I have not  been able to
reproduce since: the X screen went dark after timing out (as normal) but it
wouldn't light up again for keyboard presses, mouse clicks etc. I ahve tried
numerous time to reproduce this but not managed, so I have to say the patch is
good.