linux kernel 5.10.x to 5.11.x : boot FB switch VT is black after EFI VGA FB changed to CPU FB

[hanasaki-gmail]

linux-kernel@xxxxxxxxxxxxxxx

previous kernel 5.10...

current kernel 5.11.4

After moving to 5.11, can no longer switch to VT's.  The boot sequence 
shows as far as

fb0: switching to inteldrmfb from EFI VGA

...

Console: switching to colour dummy device 80x25

and then goes black and unresponsive.  the ^Alt-VT# keys do switch 
between X and the VT except the VT is black and unresponsive.  Booting 
to recovery mode, or just the console (uninstalled X) gets to the same 
"it appears to hang" point, although it may just be an unresponsive FB.