RX Vega 56 hangs immediately after start gdm

Submitted by Mikhail Gavrilov @Mikhail

Assigned to Default DRI bug account

Link to original bug (#105833)

Description

Created attachment 138461
dmesg

RX Vega 56 hangs immediately after start gdm

kernel: 4.16.0-rc7-git7b225300c716
mesa: 18.1.0-0.11.git6179a87
llvm: 7.0.0-0.1.r326462

Demonstration: https://youtu.be/uvsg36d9tZk

[ 23.005522] [drm:amdgpu_job_timedout [amdgpu]] ERROR ring gfx timeout, last signaled seq=1, last emitted seq=5
[ 23.005645] [drm] GPU recovery disabled.
[ 82.427656] sysrq: SysRq : Show Blocked State
[ 82.427950] task PC stack pid father
[ 121.856551] sysrq: SysRq : Show Blocked State
[ 121.856576] task PC stack pid father
[ 257.886375] sysrq: SysRq : Show Blocked State
[ 257.886399] task PC stack pid father

This is very similar to previous bugs:
[1] https://bugs.freedesktop.org/show_bug.cgi?id=105317
[2] https://bugs.freedesktop.org/show_bug.cgi?id=104001
but not needed make any action for hung occurs. It happens immediately after start graphic mode in Linux.

1. install Fedora 27.
   https://download.fedoraproject.org/pub/fedora/linux/releases/27/Workstation/x86_64/iso/Fedora-Workstation-Live-x86_64-27-1.6.iso
   
2. install latest MESA and LLVM
   https://copr.fedorainfracloud.org/coprs/che/mesa/
   
3. build and install staging kernel with latest amdgpu driver
   $ git clone git://people.freedesktop.org/~agd5f/linux --branch drm-next-4.17-wip
   $ cd linux
   $ make clean && make bzImage && make modules
   

make modules_install && make install

Reproducing issue:
1. Try to boot computer with the newly builded kernel.

Symptoms:
1. The system stop to respod.
2. All the LEDs on the video card showing the load start to glow.
3. The turbine on the video card starts to make a lot of noise.

In dmesg appears follow lines:
[drm:amdgpu_job_timedout [amdgpu]] *ERROR* ring gfx timeout, last signaled seq=1, last emitted seq=5
[drm] GPU recovery disabled.

**Attachment 138461**, "dmesg":
dmesg.txt