Thank you, Dave Arlie, and anyone else involved, for the DisplayPort
MultiStream Transport fixes in Linux 4.1.6 and 4.2 (and a few of the
subreleases and release candidates leading up to these versions).

However, I think that some change along the lines of the patch that I mentioned
may still be necessary.  I cannot be sure, because when I try to boot
linux-4.1.6, I get a other kernels bugs either before I get a chance to test
this or while I am testing it.  I am pretty sure I tried Linux-4.2 and observed
the kernel getting fault that would go away when I would apply the attached
patch.

It looks to me like, toward the end of drm_dp_add_port in Linux-4.2, I still
see the following code:

                       drm_dp_send_link_address(mstb->mgr, port->mstb);
                       port->mstb->link_address_sent = true;

...and drm_dp_send_link_address has this line, which I think can call a
function that can change port->mstb:

                       (*mgr->cbs->hotplug)(mgr);