A websearch did bring me here last week. Now I'm back to report my observation.
The slow startup plus the
[ TIME ] Timed out waiting for device dev-ttyGS0.device.
[DEPEND] Dependency failed for Serial Getty on ttyGS0.
appears to me when I have systemd-networkd enabled.
The issue seems to be that systemd-networkd waits for all network interfaces it is told about.
For quick startup and avoidance of the time-out, I have changed /etc/systemd/network/10-foo-lan3.network
[Match]
Name=lan3
[Network]
LinkLocalAddressing=no
Bridge=lan
into
[Match]
Name=lan3
[Link]
RequiredForOnline=no
[Network]
LinkLocalAddressing=no
Bridge=lan
So the trick seems to be the
[Link]
RequiredForOnline=no
I do read it as don't wait for interface lan3 getting link.
Because I have more simular interfaces as lan3, I have set there also RequiredForOnline=no
Regards
Geert Stappers
Looking forward to see yes, that link RequiredForOnline=no worked for me also.