[Intel-gfx] black screen if sna & TearFree

[Grant]

I'm using a Dell XPS 13 laptop on Gentoo and if I use:

Option "AccelMethod" "sna"
Option "TearFree" "true"

my video tearing problem disappears, but if I close my laptop lid for
a few minutes, it comes back up with a black screen, although I can
get my session back if I switch to VT1 and then back to VT7.  I can't
find anything in the logs.  I've tried xf86-video-intel-2.20.3 as well
as the latest from git.  The problem doesn't occur without the above
two directives.

Does anyone know how to diagnose or fix this?

- Grant