Comment # 18 on bug 978262 from Wolfgang Bauer

(In reply to Egbert Eich from comment #16)
> @kde-maintainers: is this issue addressed in sddm (and kdm)?

Not yet.
I had a look, and kdm adds "-nolisten tcp" to the X command line if
DISPLAYMANAGER_XSERVER_TCP_PORT_6000_OPEN="no" and nothing otherwise.
So it is affected apparently.

This is handled in the shell script /usr/share/kde4/apps/kdm/read_sysconfig.sh
lines 70ff., added by the patch kdm-sysconfig-values.diff.

I'll work on fixing this, although I am wondering whether we actually need a
version check:
I doubt that Xorg will ever be downgraded to < 1.17 in Leap or Tumbleweed, and
a workaround for users of older distributions (that upgrade their Xorg) would
be to add "-listen tcp" to DISPLAYMANAGER_KDM_LOCALARGS (in
/etc/sysconfig/displaymanager).

sddm is not affected really, AFAICT it doesn't read/respect
DISPLAYMANAGER_XSERVER_TCP_PORT_6000_OPEN at all.
You can specify command line arguments via the ServerArguments option in
/etc/sddm.conf, the default is "-nolisten tcp".

So, currently sddm unconditionally starts Xorg with "-nolisten tcp" by default,
regardless of DISPLAYMANAGER_XSERVER_TCP_PORT_6000_OPEN.
That's not a regression though, rather a (missing) feature.
We probably could add handling of DISPLAYMANAGER_XSERVER_TCP_PORT_6000_OPEN,
but I suppose that's out of scope of this bug report.