Comment 16 for bug 1863390

I had the same problem with Ubuntu 20.04 LTSP client: black screen during boot, keyboard and mouse don't work, ssh works and "ring 0 stalled" messages in the system log. I had to switch to Ubuntu 18.04 which works fine.

CPU: AMD A8-5500B APU with Radeon(tm) HD Graphics

lshw -C display
  *-display
       description: VGA compatible controller
       product: Trinity [Radeon HD 7560D]
       vendor: Advanced Micro Devices, Inc. [AMD/ATI]
       physical id: 1
       bus info: pci@0000:00:01.0
       version: 00
       width: 32 bits
       clock: 33MHz
       capabilities: pm pciexpress msi vga_controller bus_master cap_list rom
       configuration: driver=radeon latency=0
       resources: irq:35 memory:c0000000-cfffffff ioport:f000(size=256) memory:feb00000-feb3ffff memory:c0000-dffff