On Thu, 25 Mar 2021, Bob Tracy wrote:

quoted

Everything worked as well as it's going to for kernel versions up
through v5.10.0.  When I boot on v5.11.0, "lightdm" starts, the screen
goes blank as usual, I get a mouse pointer as usual, and shortly after
that, the system locks up solid (completely nonresponsive except for
being able to ping it -- can't login remotely).  Recovery is via the
reset switch at that point :-(.
(...)

Same results for 5.12.0-rc4 kernel.

 I think the only feasible way of determining what has happened here is 
that you track the offending change down by bisecting the upstream kernel 
repository with `git bisect'.  Once you have it someone may help, either 
the author of the change, or the relevant maintainer, or someone else at 
[off-list ref].

  Maciej