Hello,
I have tested and found this bug to occur on the specified bisected
commit through Linux Kernel version 5.11.12.
I am running Devuan (Debian) Linux with a hand created kernel config. I'm
attaching it.

I've bisected the kernel and found the broken commit. Here's how I got
there in case you're curious: for i in "start v4.19-rc1 v4.18" bad good
good skip skip good good skip good skip good skip good good bad good good
bad good bad good bad bad good; do git bisect $i; done

The broken commit is this one:
commit 8eaf2b1faaf4358c6337785f2192055c6ef41e0d
Author: Alex Deucher <alexander.deucher@amd.com>
Date:   Mon Jul 2 14:35:36 2018 -0500

    drm/amdgpu: switch firmware path for SI parts
    
    Use separate firmware path for amdgpu to avoid conflicts
    with radeon on SI parts.
    
    Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
    Reviewed-by: Christian Knig <christian.koenig@amd.com>
    Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

 drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c | 56 +++++++++++++++++------------------
 drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c | 14 ++++-----
 drivers/gpu/drm/amd/amdgpu/si_dpm.c   | 22 +++++++------- 3 files
 changed, 46 insertions(+), 46 deletions(-)

The last few messages before the whole system, including the network
part of the LK and USB subsystem of the LK freezes up/powers down are:
#15
#16
#17
#18
#19
#20
#21
#22
#23

I think that's telling my that I have 24 threads in my 3900X.

During boot up, I don't even reach init. The whole system freezes. I
don't see any boot up messages that suggest a problem with anything. I
see only a very few massages at all. I did enable early printk.

Steps to reproduce:
1: Build kernel with my config on a bad commit.
2: Boot new kernel (with an AMD HD7770 GPU installed, of course).
3: profit.

If you even think of suggesting I upgrade to a newer GPU, recall also
that there are none in stock -- and any GPU that is is priced
unbelievably high. I'd love a newer GPU. But I'm going to have to wait
like I have been for years for RDNA's big Navi (I was hoping it was
compute/gaming oriented like a Titan. It looks like it's not.
Grrrr, more waiting...)

Thanks,
David