If a tinydm session is unable to start a dbus session automatically, e.g.
i3wm, support starting one if configured in the profile. This is useful to run
programs that require a dbus session bus, e.g. feedbackd under such desktop
environments.

It can be enabled by creating a TINYDM_START_DBUS_SESSION environment variable
in $HOME/.profile, /etc/profile, or, better still, a file under
/etc/tinydm.d/env-x11.d/ . The value must be set to "true".

Reference: https://wiki.gentoo.org/wiki/D-Bus#The_session_bus