amdgpu driver halted on suspend of shutdown

[李真能]

Hello:

         When I do loop  auto test of reboot, I found  kernel may halt 
on memcpy_fromio of amdgpu's amdgpu_uvd_suspend, so I remove suspend 
process in amdgpu_pci_shutdown, and it will fix this bug.

I have 3 questions to ask:

1. In amdgpu_pci_shutdown, the comment explains why we must execute 
suspend,  so I know VM will call amdgpu driver in which situations, as I 
know, VM's graphics card is a virtual card;

2. I see a path that is commited by Alex Deucher, the commit message is 
as follows:

drm/amdgpu: just suspend the hw on pci shutdown

We can't just reuse pci_remove as there may be userspace still
     doing things.

My question is:In which situations, there may be  userspace till doing 
things.

3. Why amdgpu driver is halted on memcpy_fromio of amdgpu_uvd_suspend, I 
haven't launch any video app during reboot test, is it the bug of pci bus?

Test environment:

CPU: arm64

Graphics card: r7340(amdgpu), rx550

OS: ubuntu 2004