AMDPU breaks suspend after kernel 5.0

[Paul Gover]

Hi Likun,

Sorry if you don't want emails like this.  I added info. to
https://bugs.freedesktop.org/show_bug.cgi?id=110258
but people on Gentoo forums said email would be better.

Git bisect lead me to you:
---------------
106c7d6148e5aadd394e6701f7e498df49b869d1 is the first bad commit
commit 106c7d6148e5aadd394e6701f7e498df49b869d1
Author: Likun Gao <Likun.Gao at amd.com>
Date:   Thu Nov 8 20:19:54 2018 +0800

    drm/amdgpu: abstract the function of enter/exit safe mode for RLC
    
    Abstract the function of amdgpu_gfx_rlc_enter/exit_safe_mode and some part 
of rlc_init to improve the reusability of RLC.
    
    Signed-off-by: Likun Gao <Likun.Gao at amd.com>
    Acked-by: Christian König <christian.koenig at amd.com>
    Reviewed-by: Alex Deucher <alexander.deucher at amd.com>
    Signed-off-by: Alex Deucher <alexander.deucher at amd.com>

:040000 040000 8f3b365496f3bbd380a62032f20642ace51c8fef 
e14ec968011019e3f601df3f15682bb9ae0bafc6 M      drivers
---------------------
Symptoms are when resuming after pm-suspend, the screen is blank or corrupt,
the keyboard dead, and syslog shows
--------------------
kernel: [   81.096666] [drm:amdgpu_job_timedout] *ERROR* ring gfx timeout, 
signaled seq=51, emitted seq=52
kernel: [   81.096671] [drm] IP block:gfx_v8_0 is hung!
kernel: [   81.096734] [drm] GPU recovery disabled.
---------------------
or similar.  The problem occurs with all kernels since 5.0 up to and including 
5.3-rc2.  My laptop is:

HP 15-bw0xx
cpu:AMD A9-9420 RADEON R5, 5 COMPUTE CORES 2C+3G
with integrated graphics:
Stoney [Radeon R2/R3/R4/R5 Graphics] [1002:98E4]

There are several similar reports on the web, most or all for Stoney hardware, 
but that might be a coincidence as laptop users are more concerned about 
suspend, and there are a lot of laptops with similar integrated graphics 
motherboards.

I'm running Gentoo with a custom kernel, the most relevant bits of the config
CONFIG_DRM_AMDGPU=y
# CONFIG_DRM_AMDGPU_SI is not set
# CONFIG_DRM_AMDGPU_CIK is not set
# CONFIG_DRM_AMDGPU_USERPTR is not set

If you tell me how, I'm willing to try to collect traces etc.

Paul Gover